AECL
SURFACE CHEMISTRY INTERVENTIONS TO CONTROL BOILER TUBE FOULING
bY
C.W. Turner, D.A. Guzonas and S.J. Klimas
The work was co-funded by Atomic Energy of Canada Limited and the Electric Power Research Institute.
Heat Exchanger Technology Branch Chalk River Laboratories Chalk River, Ontario, Canada KOJ 1JO
2000 June
AECL- 12036 EACL
UTILISATION DE LA CHIMIE DE SURFACE POUR LUTTER CONTRE L’ENCRASSEMENT DES TUBES DES GkNdATEURS DE VAPEUR
Par
C.W. Turner, D.A. Guzonas et S.J. Klimas
RliSUMk
L’adsorption d’ammoniac, de morpholine, d’ethanolamine et de dimethylamine sur la surface de magnetite et d’hematite colldidales a Cte mesuree a 25 “C. L’effet de l’adsorption sur le potentiel de surface a Cte quantifiC en mesurant le deplacement rt%ultant du point isotlectrique des produits de corrosion, et en mesurant directement la force d’interaction superficielle entre les produits de corrosion et l’Inconel600. Ces mesures ont permis d’appuyer l’hypothese selon laquelle l’adsorption d’amine influe sur la vitesse de depot de magnetite, en diminuant la force de repulsion entre la magnetite et la surface dIncone 600. La vitesse de depot d’hematite augmentait en meme temps que la concentration d’oxygene. On a determine un mecanisme pour prendre en compte l’accroissement des vitesses de depot avec des melanges de haute qualite (> 0,35) et on a demontre sa capacite a predire le comportement, conformement aux donnees experimentales et a celles de la centrale. Par suite de ces recherches, plusieurs criteres sont proposes afin de reduire l’importance des depots de produits de corrosion sur le faisceau de tubes. Un faible depot d’hematite est favorist par une faible concentration d’oxygene dissous, tandis qu’un faible depot de magnetite est favorise en choisissant une amine pour le controle du pH ayant peu tendance a s’adsorber sur la surface de magnetite. Afin de reduire au minimum l’adsorption, l’amine devrait posseder une force de base elevee et une grande <
Technologie des Cchangeurs thermiques Laboratoires de Chalk River Chalk River (Ontario) Canada KOJ 1 JO
Juin 2000
AECL- 12036 AECL
SURFACE CHEMISTRY INTERVENTIONS TO CONTROL BOILER TUBE FOULING
bY
C.W. Turner, D.A. Guzonas and S.J. Klimas
ABSTRACT
The adsorption of ammonia, morpholine, ethanolamine, and dimethylamine onto the surfaces of colloidal magnetite and hematite was measured at 25°C. The effect of the adsorption on the surface potential was quantified by measuring the resulting shift in the isoelectric point of the corrosion products and by the direct measurement of the surface interaction force between the corrosion products and Inconel600. These measurements have served to support the hypothesis that adsorption of amine affects the magnetite deposition rate by lowering the force of repulsion between magnetite and the surface of Inconel600. The deposition rate of hematite increased as the oxygen concentration increased. A mechanism to account for enhanced deposition rates at high mixture qualities (> 0.35) has been identified and shown to predict behaviour that is consistent with both experimental and plant data. As a result of this investigation, several criteria are proposed to reduce the extent of corrosion product deposition on the tube bundle. Low hematite deposition is favoured by a low concentration of dissolved oxygen, and low magnetite deposition is favoured by choosing an amine for pH control that has little tendency to adsorb onto the surface of magnetite. To minimize adsorption the amine should have a high base strength and a large “footprint” on the surface of magnetite. To prevent enhanced deposition at high mixture qualities, it is proposed that a modified amine be used that will reduce the surface tension or the elasticity of the steam-water interface or both.
Heat Exchanger Technology Branch Chalk River Laboratories Chalk River, Ontario, Canada KOJ 1JO
2000 June
AECL-12036 In a previous investigation into the effect of alternative amines on tube-bundle fouling that was jointly funded by Atomic Energy of Canada Limited (AECL) and Electric Power Research Institute (EPRI), it was shown that the surface chemistry of corrosion products has a significant influence on the particle deposition rate under flow-boiling conditions (Turner et al., 1997). For example, particles of hematite deposited at rates an order of magnitude greater than did particles of magnetite. In tests performed at constant ~HT, the deposition rate measured for magnetite depended upon the amine used for pH control. In addition, the amine with the highest base strength at 25°C (dimethylamine) resulted in the lowest deposition rate, whereas the weakest base (morpholine) was associated with the highest deposition rate. After correcting a problem associated with acidic impurities in the cover gas (most likely carbon dioxide) that resulted in excessive amounts of amine being required to achieve the desired pH, it was observed that the deposition rates for magnetite at fixed pHr were consistently lower when less amine was added.
It was postulated that the difference between the deposition rates of magnetite and hematite was due to differences in the surface charge of these oxides under the test conditions, magnetite being negatively charged at ~HT = 6.2 and hematite, positively charged. Measurements of streaming potential at 25°C (P.V. Balakrishnan and C.W. Turner, Chalk River Laboratories, unpublished results) indicate that the surface of Inconel600 should also be negatively charged under the test conditions. Thus particles of magnetite will tend to be repelled from Inconel600, whereas particles of hematite will be attracted. To account for the dependence of the deposition rate of magnetite on the nature and concentration of amine used for pH control, it was postulated that the amine was adsorbing onto the surface of magnetite and changing its surface potential. The amine will bc present in solution as both the neutral and the protonated (positively charged) species. Thus adsorption of amine onto magnetite will tend to make its surface less negative. This adtiprption should reduce the force of repulsion between magnetite and Inconel600, and lead ICY ;\ correspondingly higher deposition rate.
AECL ;md EPRI undertook a follow-up program to evaluate the hypothesis that the adsorption of amine affcds rtw Ptiicie deposition rate by altering the surface interaction potential between the particles and the wrfacc of Inconel600. The ultimate goal of this program is to identify those propenics of the amine that control the deposition behaviour and so be able to choose or design an amine that best controls tube-bundle deposition in the steam generator.
The work scope proposed for the follow-up program includes measurements of the adsorption of amine onto the surface of corrosion products and measurements to determine the effect of adsorption on the surface potential. Laser Raman spectroscopy was chosen to measure the adsorption isotherms because this technique can be applied over a wide range of temperatures. Two techniques were chosen to measure the effect of adsorption on the surface potential of the corrosion products. Measurements of the electrophoretic mobility of a metal oxide particle versus pH provides a relatively simple way to detect the adsorption of a charged species. Every metal oxide has a characteristic pH at which the surface potential is normally zero, known as the - vii - isoelectric point (IEP). Evidence for the adsorption of the positively charged species is manifested by a shift in the IEP to a higher pH. The second method used to determine the effect of adsorption of a charged species on the surface potential is Atomic Force Microscopy (AFM). Measurements of the force exerted by the surface of Inconel600 on a particle as the two are brought together can be used to deduce the surface potential. The effect of the adsorption of amine on the surface potential can therefore be determined by performing these measurements as a function of amine concentration. By combining information on the adsorption of amines and the corresponding surface chemistry modifications with the high-temperature loop deposition data, we hope to identify properties of the amine that should be optimized to reduce deposition of corrosion products on the steam generator tube-bundle. Because the measurements performed in this investigation to determine the effect of adsorption on surface potential can only be made at ambient temperature, complementary experiments are being performed at the Oak Ridge National Laboratory in a parallel program to measure the effect of the adsorption of amine on the high-temperature point of zero charge (PZC) of magnetite.
Additional loop deposition tests were also planned to complete the test matrix for amines examined in the previous investigation and to evaluate the effect of 3 additional amines- methoxypropylamine, pyrrolidine, and 4-aminobutanol-on the deposition rate of corrosion products. A detailed analysis of flow phenomena at high mixture qualities was also planned for the follow-up program to identify the cause of the high deposition rates observed in the previous investigation for mixture qualities in excess of about 0.35. Enhanced deposition at high mixture qualities was not observed in loop tests conducted in a separate program where a polyacrylic acid dispersant was added to the loop water, and the implications of this finding will be considered in this investigation. . . . - VI11 -
Table of Contents
1. EXPERIMENTAL METHODS AND ANALYSES...... 1- 1 1.1 Adsorption Isotherms ...... l-l 1.2 Electrophoretic Mobility ...... l-2 1.3 Atomic Force Microscopy (AFM)...... l-3 1.4 Surface Tension...... l-9 1.5 Loop Deposition Tests...... l-10
2. RESULTS ...... 2-l 2.1 Adsorption Isotherms ...... 2- 1 2.2 Electrophoretic Mobility ...... 2-3 2.3 Atomic Force Microscopy...... 2-5 2.4 Surface Tension...... 2- 13 2.5 Loop Deposition Tests...... 2- 14 2.6 Deposition Mechanism at High Steam Quality...... 2-21
3. DISCUSSION ...... 3-l
4. SUMMARY AND CONCLUSIONS ...... 4- 1
5. IMPLICATIONS FOR CONTROLLING TUBE-BUNDLE FOULING...... 5- 1
6. REFERENCES ...... 6- 1
7. NOMENCLATURE ...... 7-l
APPENDIX A Amine Adsorption Isotherms on Magnetite and Hematite ...... A- 1 APPENDIX B Force-Distance Curves From Nanoscope II Raw Force Data...... B- 1 APPENDIX C Loop Deposition Test Results...... C-l APPENDIX D Definition of Thermohydraulic Parameters Under Two-Phase Flow and Development of Droplet Impingement Fouling Model ...... D- 1 APPENDIX E SEM Micrographs of Tube Deposits...... E-l LIST OF FIGURES
Figure l-l Raman spectrum of 1000 mM ethanolamine solution in the absence of added magnetite, showing the various CH stretching modes. The gradual sloping baseline is the shoulder of the OH stretching mode of water...... l-2 Figure l-2 SEM micrograph of a typical magnetite sintered agglomerate glued to an AFM cantilever...... l-4 Figure l-3 AFM image of a lo-pm-by-lo-pm region of the Inconel600 coupon used in the force measurements (bottom), and a representative surface roughness profile measured from this AFM image (top) ...... l-5 Figure l-4 Comparison of surface potentials obtained from AFM force curves and from electrophoresis of magnetite particles used in the AFM experiments. All potentials are for a zero concentration of amine...... l-8 Figure l-5 Comparison of surface potentials obtained from AFM force curves and from electrophoresis of hematite particles used in the AFM experiments. All potentials are for a zero concentration of amine...... l-8 Figure l-6 The assembled cell, showing the orientation of the Inconel600 and magnetite coupons and the location of the liquid meniscus...... l-9 Figure l-7 Cell configuration used for the contact angle measurements ...... l-9 Figure l-8 Schematic of the loop used for measurements of particle deposition under single-phase forced-convection and flow-boiling conditions ...... l-11 Figure l-9 Schematic of the test section showing 3 heated and 4 unheated regions...... l-12 Figure 2-l Adsorption isotherms for dimethylamine, ammonia, ethanolamine, and morpholine onto magnetite at 25°C...... 2- 1 Figure 2-2 Adsorption isotherms for dimethylamine, ammonia, ethanolamine, and morpholine onto hematite at 25°C...... 2-2 Figure 2-3 Temperature dependence of the adsorption of dimethylamine onto the surface of magnetite ...... 2-3 Figure 2-4 Effect of 5 mM solutions of amine on the surface potential of magnetite ...... 2-4 Figure 2-5 Effect of 50 mM solutions of amine on the surface potential of magnetite...... 2-4 Figure 2-6 The effect of additions of morpholine and ammonia on the surface potential of hematite, determined from the electrophoretic mobility ...... 2-4 Figure 2-7 Successive force curves measured using the same particle-tip combination under the same solution conditions. Filled circles are advancing measurements, open circles are retracting ...... 2-6 Figure 2-8 Force curves measured between a magnetite particle and an Inconel600 surface using 3 different particle-tip combinations. (Dimethylamine series: - diamonds; Morpholine series: - open squares; Ethanolamine series; - filled triangles)...... 2-6 Figure 2-9 Some representative force-distance curves, showing the behaviour of the advancing (filled symbols) and retracting (open symbols) parts of the force curve: (a) pH25 9, hematite particle, no amine; and (b) pH25 8, hematite particle, no amine ...... 2-7 -X-
Figure 2-10 Best fit of Equation (l-6) to the force-distance data for magnetite approaching the surface of Inconel600 ...... 2-8 Figure 2- 11 Best fit of Equation (l-6) to the force-distance data for hematite approaching the surface of Inconel600 ...... 2-9 Figure 2-12 Plots of the best fit of the force curve versus separation for the system magnetite/Inconel600 as a function of morpholine concentration, at pH25 6 to 10. Units of the abscissa are mN/m. Upper, middle, and lower lines are for 0, 5, and 50 n&I amine...... 2-10 Figure 2- 13 Plots of the best fit of the force curve versus separation for the system hematite- Inconel600 as a function of morpholine concentration at pH25 6 to 10. Units of the abscissa are mN/m. Upper, middle, and lower lines are for 0,5, and 50 mM amine ...... 2-11 Figure 2-14 Photograph of the interior of the cell used to measure the contact angles (0) of a morpholine solution on Inconel 600 and magnetite, taken at 25°C...... 2-13 Figure 2-15 The effect of temperature on the wetting angle of the Inconel60&solution and the magnetite-solution interfaces ...... 2-14 Figure 2-16 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section...... 2- 15 Figure 2-17 Normalized deposition rate vs. mixture quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section...... _...... 2- 16 Figure 2-18 Normalized deposition rate vs. mixture quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section...... 2- 19 Figure 2-19 Normalized deposition rate vs. mixture quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section...... 2- 19 Figure 2-20 Build-up of radioactivity resulting from the deposition of magnetite onto the surface of Inconel600 under flow-boiling conditions. The suspension of magnetite particles was traced using “Fe so that the build-up could be followed using a ‘y-ray detector, as described in Turner et al., 1997...... 2-20 Figure 2-22 Steam-liquid velocities and film thickness vs. mixture quality ...... 2-23 Figure 2-23 Calculated droplet deposition rate vs. mixture quality...... 2-23 Figure 3-l Comparison of typical deposition behaviour versus steam quality from the H-3 loop tests with deposit loadings measured on tubes pulled from Oconee-1 and Oconee-3 ...... 3-8 Figure 4-l Effect of surface coverage of amine on the average deposition rate of magnetite under flow-boiling conditions...... 4- 1 Figure 5-l Trends in magnetite and hematite deposition rate with water chemistry under flow-boiling conditions...... 5-2 Figure A- 1 Raman intensity versus amine concentration for dimethylamine, ammonia, ethanolamine, and morpholine. Linear fits to the data constrained to go through the origin are shown ...... A-l - xi -
Figure B-l Typical raw data output from atomic force microscopy (AFM). Regions of zero force and of constant compliance are indicated...... B-l Figure B-2 Fits of F/r versus separation for the system magnetite-Inconel600 as a function of ammonia concentration for pH = 6 to 10. The concentration of added amine is indicated in units of mM. Units for F/r are mN/m. Energy required by a l-pm particle to surmount a force barrier of 0.04 mN/m is 49kT...... B-3 Figure B-3 Fits of F/r versus separation for the system magnetite/-nconel600 as a function of ethanolamine concentration for pH = 6 to 10. The concentration of added amine is indicated in units of r&I. Units for F/r are mN/m. Energy required by a l-pm particle to surmount a force barrier of 0.04 mN/m is 49kT ...... B-4 Figure B-4 Fits of F/r versus separation for the system magnetite-Inconel600 as a function of dimethylamine concentration for pH = 6 to 10. The concentration of added amine is indicated in units of n&l. Units for F/r are mN/m. Energy required by a I -l.trn particle to surmount a force barrier of 0.04 mN/m is 49kT ...... B-5 Figure B-5 Fits of F/r versus separation for the system hematite-Inconel600 as a function of ammonia concentration for pH - 6 to 10. The concentration of added amine is indicated in units of n-&I. Units for F/r are mN/m. Energy required by a I -pm particle to surmount a force barrier of 0.04 mN/m is 49kT ...... B-6 Figure B-6 Fits of F/r versus separation for the system hematite-/Incone as a function of ethanolamine concentration for pH = 6 to 10. The concentration of added amine is indicated in units of n&l. Units for F/r are mN/m. Energy required by a 1 -pm particle to surmount a force barrier of 0.04 rnN/m is 49kT ...... B-7 Figure B-7 Fits of F/r versus separation for the system hematite-Inconel600 as a function of dimethylamine concentration for pH - 6 to 10. The concentration of added amine is indicated in units of mM. Units for F/r are mN/m. Energy required by a I -pm particle to surmount a force barrier of 0.04 mN/m is 49kT ...... B-8 Figure C-t Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section ...... c-4 Figure C-2 Normalized deposition rate as a function of steam quality. 0 indicates locations ;Ilong the heated (diabatic) test section. q indicates locations on the unheated t ddutic 1 test section ...... c-4 Figure C-3 Sormalr/.ed deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section ...... c-5 Figure CA Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section ...... c-5 Figure C-5 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section ...... C-6 Figure C-6 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section ...... C-6 - xii -
Figure C-7 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section ...... c-7 Figure C-8 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section ...... c-7 Figure C-9 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section ...... C-8 Figure C-10 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section ...... C-8 Figure C-l 1 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section ...... C-9 Figure C-12 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section ...... C-9 Figure C-13 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section ...... C- 10 Figure C-14 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section ...... C-10 Figure C-15 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section ...... C- 11 Figure C-16 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. q indicates locations on the unheated (adiabatic) test section ...... C- 11 Figure C-17 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section ...... C- 12 Figure C-18 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section ...... C-12 Figure C-19 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section ...... c-13 Figure C-20 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section...... C- 13 Figure C-21 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section . . ..1...... 1..11...... I...... 11....,,,,,,,,,..,...... 1.....1..1...1..11 c-14 . . . - Xl11 -
Figure C-22 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section ...... c-14 Figure C-23 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section ...... C- 15 Figure C-24 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section ...... C- 15 Figure C-25 Magnetic flux density from axial and transverse direction ...... C-17 Figure D-l Schematics of the steam quality change during a non-equilibrium 2-phase flow. Re-printed from Tong and Tang (1997) should the reference be Hsu and Graham (1986)?...... D-l Figure D-2 Hewitt and Roberts flow pattern map (Whalley, 1987) for vertical upwards flow inside a tube...... D-3 Figure E- 1 Morphology of surface deposits created under magnetite/morpholine chemistry, Experiment D097...... E-2 Figure E-2 Morphology of surface deposits created under magnetite/morpholine chemistry, run D119...... E-3 Figure E-3 Morphology of surface deposits created under magnetite/ammonia chemistry, run D120...... E-4 Figure E-4 Morphology of surface deposits created under magnetite/dimethylamine chemistry (DlOO and DlO5) ...... E-5 Figure E-5 Morphology of deposits created under magnetite/potassium hydroxide chemistry...... E-6 Figure E-6 Morphology of surface deposits created under magnetite/pyrrolidine chemistry control...... E-7 Figure E-7 Morphology of surface deposits created under magnetite/3- methoxypropylamine chemistry (experiment D102)...... E-8 Figure E-8 Morphology of surface deposits created under magnetite/4-aminobutanol chemistry...... E-9 Figure E-9 Morphology of surface deposits created under hematite/ethanolamine chemistry, D108 and Dill...... E-10 Figure E- 10 Morphology of surface deposits created under hematite/dimethylamine chemistry, hydrazine present, no oxygen, experiment D 106...... E- 11 Figure E- 11 Morphology of surface deposits created under hematite/potassium hydroxide chemistry D113 and D115...... E-12 Figure E- 12 Morphology of surface deposits created under hematite&methoxypropylamine chemistry, experiment Dl 10 ...... E-13 Figure E- 13 Morphology of surface deposits created under hematite/3methoxypropylamine chemistry, experiment D 112 ...... -...... E-14 LIST OF TABLES
Table l-l Surface potentials determined for Inconel600, magnetite, and hematite from electrokinetic data...... l-6 Table l-2 Nominal loop conditions for the deposition tests ...... l-10 Table l-3 Concentrations of amine required to achieve pHr = 6.2 at 270°C...... l- 11 Table 2-l Amine adsorbed at concentrations of 5 and 50 n&I...... 2-2 Table 2-2 Surface potential of magnetite in mV, determined by fitting Equation (l-6) to the AFM force-distance data...... 2- 12 Table 2-3 Surface potential of hematite in mV determined by fitting Equation (l-6) to the AFM force-distance data...... 2-l 2 Table 2-4 Surface charge density (mC/m2) calculated for magnetite from Equation (l-7)....2-13 Table 2-5 Surface charge density (mC/m2), calculated for hematite from Equation ( 1-7). ... .2- 13 Table 2-6 Listing of loop deposition tests performed in this investigation...... 2-15 Table 2-7 Summary of loop deposition results for magnetite...... 2-17 Table 2-8 Summary of loop deposition results for hematite...... 2-20 Table 3-l Comparison of trends in amine base strength, molecular size, and the relative amount adsorbed onto corrosion products for 5 and 50 mM concentrations of amine...... 3-2 Table 3-2 Calculated change in surface charge density with adsorption of amine for the second limiting case ...... 3-4 Table 3-3 Summary of deposition results for magnetite. Results of the current investigation are shown in bold, and the other results are from Turner et al. (1997)...... 3-5 Table 3-4 Relationship between surface coverage of amine and the average magnetite deposition rate under flow-boiling conditions ...... 3-6 Table 3-5 Summary of deposition results for hematite. Results of the current investigation are shown in bold, and the other results are from Turner et al., 1997...... 3-7 Table B- 1 Change in the surface charge density (mC/m2) on magnetite after the adsorption of amine. A positive change corresponds to a surface that is less negative. A surface charge density of 1 mC/m2 corresponds to approximately 1 electronic charge per 200 nm2...... B-9 Table B-2 Change in the surface charge density (mC/m2) on hematite following the adsorption of amine. A positive change corresponds to a surface that is less negative. A surface charge density of 1 mC/m2 corresponds to approximately 1 electronic charge per 200 nm2...... B-9 Table C-l Loop chemistry and operating conditions for each test ...... C-l Table C-2 Database of all the H3 loop deposition results for magnetite, FesO4...... C-2 Table C-3 Database of all the H3 loop deposition results for hematite, Fe203 ...... C-3 1. EXPERIMENTAL METHODS AND ANALYSES
1.1 Adsorption Isotherms
Adsorption of the amines onto suspensions of magnetite or hematite particles was determined by measuring the amount of amine removed from solution in contact with the corrosion product. Four amines were included in the investigation: morpholine, ammonia, ethanolamine, and dimethylamine. The magnetite was synthesized using a procedure developed by Sugimoto and Matijevic (1980), whereas the hematite was reagent-grade chemical purchased from Fisher Scientific Co. Both oxides were thoroughly rinsed in solutions of acid and base and then in distilled water, before measurements were made.
A measured amount of oxide (approximately 4 mg) was added to a fixed volume of solution with a known concentration of amine, and the suspension was adjusted to pH 10 using potassium hydroxide. The suspension was then thoroughly mixed in an ultrasonic bath for 1 h and then left for 24 h to equilibrate. After equilibration, the suspensions were filtered and the concentration of amine in the filtrate was measured using Laser Raman spectroscopy. This method of analysis was chosen because it can be applied over a range of temperatures. Surface areas for the magnetite and hematite particles used in these experiments were determined by nitrogen adsorption using the Brunauer-Emmett-Teller (BET) method (Brunauer et a1.,1938). Values of 3.98 m’/g and 9.62 m2/g were obtained for magnetite and hematite, respectively.
A typical Raman spectrum from a solution of ethanolamine is shown in Figure l-l. Raman spectra were excited, using the 514.5-nm line of an Ar+ ion laser with an incident power of about 1.5 W. The scattered light was collected and analyzed using a SPEX 1.0-m monochromator and charge-coupled-device detector. The spectra were stored on a PC running SPEX DM3000 softuarc. Detector integration times ranged from 1 to 40 s, depending upon the amine concentr;rtton in solution. Sixteen scans were averaged for each measurement. Data were further manipul;rtcd using GRAMS/386 software (Galactic Industries). For room-temperature meawrcmcnt$. the spectra were acquired in square silica cuvettes, having a path length of 1 .O cm. The high-temperature measurements were made using a Graseby-Specac heated infrared cell. u-tth uhca w mdows and an automated temperature controller. For measurements at elevated temprmturcs. the particles were allowed to settle out of the beam before measurements were made.
Calibration curves of Raman intensity as a function of solution concentration were prepared by measuring the Raman spectra of amine solutions at concentrations of 1, 10, 100 and 1000 n&I. For quantification, the CH stretching and bending modes of the amines were selected because they are intense, occur at frequencies free of interference from water bands, and their intensities were not expected to be significantly perturbed by changes in concentration. Plots of the Raman intensity versus concentration for each of the 4 amines are linear over the 3-decade concentration range examined, as shown in Figure A-l of Appendix A of this report.
For the adsorption isotherms measured at room temperature, the spectra of both the starting solution and of the solution + oxide were measured sequentially. For each solution
l-l concentration, the water bending mode at -1600 cm-’ was used as a reference to compensate for the small variations in laser power, sample alignment, and spectrum acquisition times’. The same cuvette was used to measure all the Raman spectra. The spectrum of the solution + oxide was subtracted from the spectrum of the starting solution, and the intensity of the difference band was used to determine the amount of amine adsorbed, as described in Appendix A of this report.
=E Eooo- sa .5%6OCQ- ii E ooc- ii4 E 2 2ooo-
O-J I I I I I 2600 264x 2700 2600 2900 3ooo
Raman Shift (cm -)
Figure l-l Raman spectrum of 1000 mM ethanolamine solution in the absence of added magnetite, showing the various CH stretching modes. The gradual sloping baseline is the shoulder of the OH stretching mode of water.
1.2 Electrdphoretic Mobility
Stock suspensions of the corrosion products used for the measurements of electrophoretic mobility were stored in clean stainless steel vessels, to avoid possible contamination by silica. Dilution of the suspensions and final adjustments for pH and amine concentration were done using a dedicated set of glassware that had been washed with potassium dichromate and thoroughly rinsed with de-ionized water. All water used in this investigation was purged with ultra-high-purity argon to remove dissolved oxygen and carbon dioxide and was stored in a sealed glass carboy.
Electrophoretic mobilities (velocity per unit electric field) of particles in suspension were measured at room temperature in a commercial apparatus supplied by Zeta-Meter, I&. For these measurements, a suspension of particles is placed in a quartz capillary, and an electric field
’ At high amine concentrations in solution, only short detector integration times were used during data acquisition to avoid saturation of the detector. As the amine concentration in solution decreased, longer integration times were required to achieve adequate signal-to-noise ratios. * Zeta-Meter System 3.0
l-2 is then applied along the axis of the capillary. The sample is illuminated from the side so that the motion of the particles can be observed with the aid of a low-powered microscope. Velocity is determined by measuring the time taken for a particle to cross a calibrated grid.
Many factors can influence the electrophoretic mobility and isoelectric point (IEP) of a colloidal suspension. Thus for each amine concentration, a fresh suspension of magnetite or hematite was prepared from the concentrated stock suspension, and all samples (i.e., 4 different amines plus a reference with no amine added) were processed and measured batchwise. For each sample, an aliquot of the stock suspension was diluted in a 0.5 mM solution of potassium nitrate. The required amount of amine was then added, and the pH was adjusted by the addition of either KOH or KC104. The samples were then agitated in an ultrasonic bath for 20 min and left for 24 h to equilibrate. Previous experience has shown that in the absence of the amine the suspensions reached equilibrium within 1 or 2 h of adjusting the pH, but longer times were required in the tests for which an amine was present.
Electrophoretic mobilities were measured for pH ranging from 5 to 10 in the presence of 5 and 50 mM concentrations of amine and were compared to the mobilities measured in the absence of amine. From 12 to 14 particles were tracked, and their electrophoretic mobilities were measured for each set of conditions. Duplicate measurements were made on freshly prepared samples to ensure the reproducibility of the method. Electrophoretic mobility was converted to zeta potential, defined as the potential at the plane of shear between the particle and the solution, using the equation developed for the case where the particle radius is large compared to the diffuse layer thickness (Hiemenz, 1977):
D ET 0 c u = U-1) P
Atomic Force Microscopy (A FM)
Interaction forces between the surfaces of Inconel600 and either magnetite or hematite particles were measured using a Nanoscope II Atomic Force Microscope (AFM). Agglomerates of magnetite and hematite colloidal particles, suitable for force measurements, were prepared by sintering magnetite and hematite particles at 750°C for 1 h. Magnetite was heated under an atmosphere of ultra-pure argon to prevent oxidation, whereas hematite was heat-treated in air. The diameters of the agglomerates were measured by scanning electron microscopy (SEM) at the completion of the experiments. An SEM micrograph of a typical sintered agglomerate of magnetite particles is shown in Figure l-2. The agglomerates were roughly spherical and had diameters in the range 2 to20 pm. The magnetite or hematite agglomerates were glued to the tip of a standard AFM cantilever, using the method of Ducker et al. (1991).
l-3 Figure 1-2 SEM micrograph of a typical magnetite sintered agglomerate glued to an AFM cantilever.
Inconel 600 coupons were polished to a 0.06~pm finish using alumina and were then autoclaved at pH2.5 9 with morpholine at 250°C for several days to grow an oxide film. The resulting surface was relatively smooth, as shown in Figure l-3. The average surface roughness of the Inconel 600 substrate was measured by AFM to be -25 nm. The same coupon was used throughout the measurements. Between each set of measurements, the surface was lightly polished with 0.06 l_trn alumina and then was agitated in an ultrasonic bath for 30 min in methanol.
The force curves were measured at 25 “C in aqueous solution using the manufacturer’s fluid cell. The entire AFM assembly (head, fluid cell, tip) was allowed to come to thermal equilibrium for 1 to 2 h before starting the measurements. The addition of fresh solution to the cell required a minimum of 15 min before thermal drifts had stopped. From 6 to 10 force curves were measured for each solution. Thus about 100 force curves were acquired for a single set of measurements with either magnetite or hematite and 1 amine at 2 different concentrations.
A single agglomerate-tip combination was used to measure force curves at 0, 5 and 50 mM concentrations of each amine. The force-distance curves were measured in the fluid cell over the pH?s range 6 to 10 in increments of 1 pH unit. After the addition of amine, the solutions were adjusted to the appropriate pH by additions of KOH and KCl04. For each new solution, 10 mL of solution were passed through the cell before adding the final aliquot. This IO-mL aliquot represents several cell volumes and ensured that all traces of the previous solution were flushed from the cell. After allowing time for adsorption, a fresh aliquot of solution was added to the cell just before the measurements were taken, to ensure that the solution in contact with the surface was not depleted in amine.
1-4 The Nanoscope II software does not directly provide an output file containing the force-curve data. A discussion of the process used to convert the Nanoscope II output to force-distance curves is presented in Appendix B of this report. The total force of interaction between the agglomerate and Inconel6OO coupon was converted to an interaction energy per unit area by dividing the total force by 27tr. For 2 charged surfaces that are not in contact with one another, there are 2 main contributions to the total interaction energy: one arising from the van der Waals interaction and the other from the overlap of the diffuse layers of ionic charge in solution adjacent to a charged interface (see, for example, Hiemenz (1977) for a full discussion of both interactions). The van der Waals force is generally attractive with a magnitude that is dependent upon both geometry and the Hamaker constant for each of the component materials. The diffuse-layer interaction results in a repulsive force if both surfaces have the same sign of charge. The magnitude of the repulsive force depends upon the ionic strength of the solution and the 2 surface potentials.
A complete analysis of the force curves requires knowledge of the Hamaker constants and surface potentials for each of the materials involved. Under the circumstances, however, several assumptions could be made that greatly simplified the analysis without significantly changing the result. The first assumption was that the surfaces had potentials of similar magnitude in the region of interest, i.e., pH25 > 7. Table l-l lists surface potentials deduced by various measurements for the 3 surfaces involved. The surface potential of Inconel600 was determined from measurements of the streaming potential (P.V. Balakrishnan and C.W. Turner, Chalk River Laboratories, unpublished results), whereas surface potentials for magnetite and hematite were determined from the electrophoretic mobilities reported in Section 2.2. It is clear from the table that all 3 surfaces are negatively charged and have potentials of approximately the same magnitude for pH2s > 7. Thus the simplifying assumption that all 3 surfaces have similar surface potentials is justified, at least in the absence of adsorbed amine.
Figure 1-3 AFM image of a lO-pm-by-lo-pm region of the lnconel600 coupon used in the force meawrements (bottom), and a representative surface roughness profile measured from this AFM image (top).
l-5 Table l-l Surface potentials determined for lnconel600, magnetite, and hematite from electrokinetic data.
8.0 -31.0 8.5 -39.5 -28.6 9.2 -47.2 9.6 -35.6 -32.7 a from streaming potential measurements b from electrophoresis measurements (Section 1.2) The second simplifying assumption made was that the Hamaker constants (see Equation 1-5) for the 3 surfaces are approximately the same. Since the Inconel600 coupons had been autoclaved, it is the Hamaker constant of the surface oxide film that is important and not that of the underlying metal. A Hamaker constant of 9 x 10e2’ J was used for the magnetite-water-Inconel system. determined from previous measurements of the interaction force between magnetite particles and the surface of a single crystal of magnetite (D.A. Guzonas, Chalk River Laboratories. unpublished results). For the hematite-water-Inconel system, a Hamaker constant of 5 x IO ” J u’;L\ used because hematite is a less conductive oxide than magnetite.
The third \tmplifying assumption made for the analysis of the force data was the “linear supcrpo\mon approximation” to calculate the total repulsive potential between the surfaces as a function of rp;u;ltlon. This approximation is good for separations for which ti >>l , where
8m2zn K2 =DE,kT* (l-2)
K is related to the ionic strength of the solution and is a measure of the thickness of the diffuse ionic layer of charge in the solution adjacent to the charged interface. (To a good approximation, the diffuse layer of charge decays exponentially with increasing distance from the charged surface, with a decay constant equal to K). For the AFM measurements, K ranged from 0.14 to 0.25 nm-‘, which corresponds to diffuse layers that extend 20 to 30 nm into the solution from the charged surface (Hiemenz, 1977). The diffuse layers are, thus, thin enough compared to the size of the agglomerate on the AFM tip that the force of repulsion between the agglomerate and the polished Inconel600 coupon can be calculated on the basis of repulsion between 2 flat surfaces.
l-6 In this case, the principle of linear superposition leads to the following expressions for the repulsive potential:
64nkT w,, =-K Y2 exp(-ti) (l-3)
exp(ze +Y / 2kT) - 1 ’ = exp(ze ly / 2kT) + 1 (l-4)
Because interaction potentials in water generally only become significant for separations that are small compared to the sample dimensions, the expression for the van der Waals attractive potential between flat surfaces was used in the analysis. Thus,
A Wvdw =-- 12h . (1-5)
The total interaction potential between the 2 surface is given by the sum of Equations (l-3) and (l-5):
Wt0t = Wdl+ Wvdw . U-6)
Finally, the surface potential, w, is determined by fitting Equation (l-6) to the force-distance curves using the assumptions discussed above.
Values for the surface potentials determined by fitting Equation (l-6) to the force-distance data are compared to those obtained by electrophoresis for magnetite and hematite in Figures l-4 and 1-5, respectively. The zeta potentials and the surface potentials derived from AFM data are generally in good agreement above pHz 7, suggesting that the simple treatment of the surface- force data, described above, is sufficient. One exception comes from the analysis of the hematite-Inconel600 force curve for the morpholine series of measurements, where the derived surface potential is zero between pHz5 6 and 8. This behaviour was peculiar to the particular hematite particle chosen for this series of measurements.
l-7 . .D
! I 5 6 7 6 9 lb
PH
Figure 1-4 Comparison of surface potentials obtained from AFM force curves and from electrophoresis of magnetite particles used In the AFM experiments. All potentials are for a zero concentration of amine.
40
30 --
PH Figure 1-5 Comparison of surface potentials obtained from AFM force curves and from electrophoresis of hematite particles used in the AFM experiments. All potentials are for a zero concentration of amine.
From the surface potentials, the surface charge density can also be calculated:
o=Jmsinh (l-7)
l-8 1.4 Surface Tension
A relatively simple method was devised for measuring the inter-facial tension of water at the Inconel 600-water and magnetite-water interfaces as a function of temperature. The same high-temperature cell that was used for the laser Raman measurements was also used to determine the interfacial tension by measuring the wetting angle at selected temperatures. A coupon of Inconel600-identical to the one used for the AFM measurements-and a single crystal of magnetite were placed into the cell, which was then filled with a solution of morpholine at pH 9.5. The 2 flat surfaces of the Inconel600 coupon and the magnetite single crystal were arranged parallel to one another so that the wetting angle of the morpholine solution could be recorded by photography at a magnification of 10X through the quartz window of the cell. Photographs were taken at selected temperatures from 25°C to 140°C, and the wetting angle on each surface was measured from the photographs. A schematic showing a view through the quartz window of the filled cell and the menisci at the water-Inconel600 and water- magnetite interfaces is shown in Figure l-6.
steel holder
magnetite coupon
Figure 1-6 The assembled cell, showing the orientation of the lnconel666 and magnetite coupons and the location of the liquid meniscus.
Figure l-7 shows the configuration of the windows and spacers used to contain the liquid and the magnetite and Inconel600 coupons for the measurements. A rectangular Inconel600 coupon measuring 10 mm x 20 mm was cut and polished on one side to a mirror finish using polishing grits down to a final grit.size of 1 pm. A thin, near-rectangular magnetite coupon measuring 10 mm x 15 mm was cut from a sample of magnetite of geologic origin (Bentley Lake, Ontario), and polished to a 1-p,rn finish. The magnetite and Inconel600 coupons were placed between the quartz windows of the cell (within the IO-mm Teflon spacer) and held apart by a Teflon plug. About 2 mL of the solution of interest was then added to the cell, and the loaded cell was placed in the stainless steel holder and was bolted.
O.lmm tcflmn spacer
2mm quartz window
IOmm trflmn spacer
21mm quartz window
Figure 1-7 Cell configuration used for the contact angle measurements.
l-9 The contact angle (e), defined as the angle measured in solution between the solid-liquid and liquid-vapour interfaces, is determined by the surface tensions of 3 interfaces: solid-liquid, solid- vapour, and liquid-vapour. Their relationship is given by the equation of Young and Dupre (Vold and Vold, 1983):
Ysv - YSL c0se= (l-8) YLV If the contact angle at the liquid-solid interface (measured within the liquid) is less than 90”, then the liquid will spontaneously spread over the surface, whereas if the contact angle is greater than 90”, the liquid is said to be non-wetting. Equation (l-8) states that the liquid will spread provided that ysv > ys~, whereas it will be non-wetting if ysv c ys~. Where the liquid is water, the 2 surfaces would be referred to as hydrophilic and hydrophobic, respectively. Equation (l-8) can be used to compare the relative hydrophobicity of 2 different surfaces for measurements with a single liquid, or it can be used to measure trends in the surface tension of a series of liquids or solutions for measurements made on a single surface.
1.5 Loop Deposition Tests
The experimental test procedures are discussed in detail in Turner et al., (1997), and will not be repeated here. A schematic of the loop used for the deposition tests is shown in Figure 1-8, and the nominal conditions used for the deposition tests are listed in Table l-2. Theoretical concentrations of amine required to achieve pHr = 6.2 at 270°C are listed in Table l-3.
Table l-2 Nominal loop conditions for the deposition tests.
I Pressure I Heat Flux I Mass Flux I T_-_-_---..saturntin” I Oualib- _ I MPa kW/m’ kg/m’s “C _ 5.6 230 300 270 -0.28 - +0.55
A typical test consisted of bringing the loop to stable operating conditions and holding it there for a period of approximately 48 h while the suspension of corrosion products was being equilibrated with amine at the required pH. Corrosion products used in the deposition tests were from the same source as those used for other parts of this investigation, i.e., measurements of adsorption isotherms, electrophoresis, and AFM. The suspension of corrosion products was traced using 5gFe, to facilitate on-line measurement of the deposition rate. The deposition phase of the test was initiated by starting the injection of the suspension of corrosion product into the loop. Particles were injected upstream of the test section and were filtered downstream, so the particles in suspension made just a single pass through the test section.
l-10 Table 1-3 Concentrations of amine required to achieve pHT = 6.2 at 270°C.
pH Control Reagent (as Relative ~Hnooc ~Hwc Concentration Concentration anhydride) Molecular of Free Amine, Mass, - mgikg Morpholine 87.12 6.20 9.26 10.7 Ethanolamine 61.08 6.20 9.53 4.3 Ammonia 17.0 6.20 9.64 2.6 Dimethylamine 45.08 6.20 9.14 0.63 10” I\ mr\ “_ I r-3 A .n-5 3-Methoxypropylamine 89.14 6.20 I Y.IU I 1.3 I U.L x IV - n AA Qc-3 9 9 _. 1 n-5 4-Aminobutanol 89.0 6.20 I 7.V-t I I 3.3 A 1” Pyrrolidine 71.12 6.20 9.13 of& 1.4 x IO” 1 KOH I 56.1 I 6.20 I 8.93 0.47 I 8.4 x 1C6
A schematic of the test section with 3 heated and 4 unheated regions is shown in Figure l-9. The direction of fluid flow is now upwards in all regions where deposition rates are measured. This modification is an improvement over the test section used for the previous investigation where the flow direction was downward in the unheated regions. The steam qualities in the 4 unheated sections are approximately - 0.28 (single-phase forced convection), 0.03 (2-phase forced convection), 0.23 (2-phase forced convection), and 0.50 (annular flow).
Sample Sample Filter Cooler
Slurry Tank
,+j--%$Z
Filter
Slurry Addition Pump
Test Sections: Al to Al-adiabatic Dl to D3-diabatic
A”,%2&*fiskgvzch Schematic of the H-3 Fouling Loop (B-250) Figure 1-6 Schematic of the loop used for measurements of particle deposition under single-phase forced-convection and flow-boiling conditions.
Additional equipment was installed on the loop to improve the measurement of electrical power dissipated in each region of the test section. This upgrade permits a more accurate evaluation of local heat flux, steam quality, and heat-transfer coefficient. The temperature at the inlet to the test section is now regulated using a by-pass valve connected to a temperature controller on the loop interchanger. This modification has eliminated drift in the inlet temperature and has improved the stability of the tests. An 18-L stainless steel tank was manufactured to hold the concentrated slurries of magnetite
l-11 and hematite that are injected into the loop during each test. The replacement of the glass carboy with a stainless steel tank eliminates the concern over silica contamination of the corrosion products. The data acquisition system was expanded from 30 to 80 channels. The heat-transfer coefficients can now be evaluated at several locations during each test. A commercial Hall-effect probe was acquired, and its sensor was modified to make it suitable for measuring the magnetic field inside the test section. The results of these measurements, which are included in Appendix C of this report, show that the intensity of the magnetic field in the fluid inside the test section is too small to influence the particle deposition rate. The electrical conductivity of the loop water is now monitored continuously during each test. Although not a specific test parameter, this approach provides an additional check on the chemistry control from one test to another.
EoutB/l
-TEoutl/ TEo
Test Section Drain
Test Sections: Al to A4-adiabatic t Dl to DJ-diabatic Tnnt Cn0tinn lb-Pinat
AECL, Chalk River Laboratories Heat Exchanger Technology Branch
1 SCHEMATIC OF THE B250 H-3 LOOP TEST SECTION 1
Figure 1-9 Schematic of the test section showing 3 heated and 4 unheated regions.
These upgrades to the main loop and test section were completed before starting the current set of loop tests, and have resulted in an improvement in the reliability and quality of the loop test data.
1-12 2. RESULTS
2.1 Adsorption Isotherms
Adsorption isotherms for the 4 amines examined are shown in Figures 2- 1 and 2-2 for magnetite and hematite, respectively. The isotherms for adsorption of amine onto magnetite show a steep rise in the amount adsorbed over the concentration range 1 to 100 mM, followed by a more gradual increase between amine concentrations of 100 and 1000 mM. Adsorption per gram oxide was converted to adsorption per unit area using the specific surface area of the oxides (see Section 1.1). Adsorption onto magnetite at 25°C decreases in the following order: ammonia > dimethylamine > ethanolamine = morpholine.
40 .
0 200 400 600 800 1000 0 200 400 600 800 1000 [Dimathylamine] (mM) I [Ammonia] (mM)
1 -4 200 400 600 800 1000 0 500 1000 [Ethanolamine] (mM) [Morpholine] (mM)
Figure 2-1 Adsorption isotherms for dimethylamine, ammonia, ethanolamine, and morpholine onto magnetite at 25°C.
The isotherms for adsorption of amine onto hematite, shown in Figure 2-2, are qualitatively similar to those measured for magnetite, but the adsorbed amounts are higher by a factor of -2 for DMA, morpholine and ethanolamine, and higher by a factor of -4 for NH3 . As in the case of magnetite, the amount adsorbed at all amine concentrations decreases in the order ammonia > dimethylamine > ethanolamine * morpholine.
The amounts of amine adsorbed onto magnetite and hematite at concentrations of 5 and 50 mM (deduced by linear interpolation of the isotherms in Figures 2-l and 2-2) are listed in Table 2-l. The number of molecules adsorbed per unit area (BET specific surface area) at both amine
2-l concentrations is higher than expected for monolayer adsorption, suggesting either multilayer adsorption or an underestimation of the specific surfaces areas of the oxides. To check on the reproducibility of the data, the amount of amine adsorbed at an amine concentration of 1000 mM was re-measured for selected amine-oxide combinations. Higher oxide loadings were used for these measurements in case the apparent multilayer adsorption was an artifact of the small amount of oxide used for the previous measurements. In addition, measurements were made after l-h and 24-h equilibration times. For each case, the amount of amine adsorbed was in good agreement with the numbers listed in Table 2-1, thus showing that the measurements are reproducible, are not dependent upon oxide loading, and that the oxide surface has equilibrated with the amine within 1 h.
60 D 2 50 b G- a P40u) E +30 ‘$ E 2 -E 20 F E 10 s 0 0 200 400 600 800 1000 200 400 600 800 1000 [Dimethylamine] (mM) [Ammonia] (mM)
-I OI 0 200 400 600 800 1000 0 200 400 600 800 1000 [Ethanolamine] (mM) [Morpholine] (mM)
Figure 2-2 Adsorption isotherms for dimethylamine, ammonia, ethanolamine, and morpholine onto hematite at 25°C.
Table 2-1 Amine adsorbed at concentrations of 5 and 50 mM. Adsorption onto Magnetite Adsorption onto Hematite molecules/nm2 moleculeshun Amine 5mM 5omM 5mM 5omM Ethanolamine 70 200 100 820 Morpholine 50 310 200 580 Dimethylamine 120 520 250 2000 ammonia 200 2800 500 2100
2-2 The temperature dependence of DMA adsorption on magnetite is shown in Figure 2-3, expressed as the percentage adsorbed at temperature referenced to the amount adsorbed at 25°C. The adsorbed amount is observed to decrease with increasing temperature, falling by about 13% between 25°C and 125°C. Considerable effort was expended trying to repeat these measurements with other amine-oxide combinations but was unsuccessful because the quartz window in the cell invariably failed above 100°C. It was eventually determined through discussions with the manufacturer that the high-temperature cell has a design flaw that causes the cell window to crack near the filling ports at temperatures not far in excess of 100°C. Recent tests with windows without filling ports were encouraging. Thus a combination of thicker windows without filling ports and the substitution of stainless steel gaskets for the Teflon ones may enable Raman spectra to be collected over the full temperature range.
100
80 0 50 100 150 Temperature (“C)
Figure 2-3 Temperature dependence of the adsorption of dimethylamine onto the surface of magnetite
2.2 Electrophoretic Mobility
Figure 2-4 shows the effect of 5 rnM solutions of amine on the zeta potential of magnetite. In the absence of amine, the zeta potential crosses zero near pH= 5.8, corresponding to an IEP of 5.8. Note that the zeta potential changes rapidly with pH in the vicinity of the IEP. The IEP in the presence of 5 mM amine ranged from 5.8 to 6.3 for three of the amines, which is within the expected range of variability of IEP from one sameple to another. Hence this variation cannot be taken as strong evidence for a shift in IEP, caused by the presence of amine. Ammonia appeared to shift the IEP to a lower value, but this was not reproducible and is likely the result of contamination of the sample.
2-3 11
PH
Figure 2-4 Effect of 5 mM solutions of Figure 2-5 Effect of 50 mM solutions of amine on the surface potential of amine on the surface potential of magnetite. magnetite.
Figure 2-5 shows the effect of 50 n-&l solutions of amine on the zeta potential and IEP of magnetite. For this set of measurements, the IEP of the reference sample is at pH25 6.7, which is in good agreement with the IEP of 6.5 for magnetite reported by Tewari and McLean (1972). In each case, the IEP of magnetite was higher in the presence of the 50 n&I solution of amine, with the shift in IEP ranging from +O.S to +1.7 pH units. The shift in IEP to higher pH in the presence of the 50 mM solutions of amine is strong evidence for the adsorption of a positively charged species onto the surface of the magnetite particles. 4o I -*_ No Amine +-No Amine 30 -+- 50 mM ammonia n --.... 920 II - l - 5mMemmonia ‘. . g - - I) - -50 mM morphdine - 10 2 - - * - -5 mM morphdine E a 0 b t-10 5 N-20
-30
-40 Figure 2-6 The effect of additions of morpholine and ammonia on the surface potential of hematite, determined from the electrophoretic mobility.
2-4 The effect of the addition of either morpholine or ammonia on the surface potential measured for hematite by electrophoresis is shown in Figure 2-6. In the absence of amine, the surface potential for hematite remains negative down to pH 4, with an estimated IEP of pH 3. This value is much lower than the IEP reported for hematite synthesized by hydrolysis of a solution of Fe(II1) (Fokkink et al., 1989; Matijevic and Schneiner (1978)) but is consistent with the IEP reported for reagent-grade hematite purchased from another commercial supplier (Jayaweera et al., 1992). The hematite used in the present investigation was washed thoroughly with acid and base to remove adsorbed impurities from the surface. Hence the probability that the deviation in IEP from that reported in the literature cited above is the result of adsorbed impurities is low. The addition of 5 mM amine had a much greater effect on the surface potential of hematite than on magnetite, shifting the IEP from an estimated pH 3 to approximately pH 6. Raising the amine concentration to 50 mM increased the IEP a further + 0.5 pH units.
2.3 Atomic Force Microscopy
Several force curves measured at pH25 10 between a hematite particle and the surface of Inconel 600 in a single experiment are shown in Figure 2-7, to illustrate the reproducibility of the data. For these measurements, a positive force signifies repulsion between the surfaces of Inconel600 and hematite, whereas a negative force signifies attraction. Figure 2-7 shows that the force between the surfaces of hematite and Inconel600 at pH2s 10 is repulsive at all separations. Since the surface of Inconel600 is negatively charged for pH& >> 4, this result shows that the surface of hematite is negatively charged at pH= 10. Both the advancing (particle approaching surface) and the retracting (particle withdrawing from the surface) force curves are shown. The spread in the force data is generally ti.5 nN, and the location of the hard wall contact was reproducible to within about 1 nm.
A check on reproducibility between experiments can be made by comparing the results of measurements made in the absence of amine using different particle-tip combinations. When the force data are scaled by F/&r, the force curves should be the same under the same solution conditions. This behaviour is indeed observed in Figure 2-8, where the reference data (i.e., zero concentration of amine) are shown for the morpholine, ethanolamine, and ammonia series of measurements for the system magnetite-water-Inconel.
2-5 Separation (nm) Figure 2-7 Successive force curves measured using the same particle-tip combination under the same solution conditions. Filled circles are advancing measurements, open circles are retracting.
6
1
0 0 10 20 30 40 50 Separation (nm) Figure 2-6 Force curves measured between a magnetite particle and an lnconel600 surface using 3 different particle-tip combinations. (Dimethylamine series: - diamonds; Morpholine series: - open squares; Ethanolamine series; - filled triangles).
Several different behaviours of the advancing and retracting force curves were observed. At high pH, the force curves were often similar to those shown in Figure 2-8, where the advancing and retracting force curves were identical and no jump into an adhesive minimum was observed. In these force curves, a repulsive force was observed starting at separations of about 30 nm. This force increased exponentially as the separation decreased. At small separations (~1 to 2 nm) the force became more steeply repulsive. The steep repulsive part of the force curve seen at small separations is attributed to the interaction of surface asperities at small separations.
2-6 Figure 2-9 shows 2 other types of behaviour of the advancing and retracting force curves. In Figure 2-9a (pH25 9, hematite particle, no amine added) the total force is repulsive upon advancing to contact, and no jump into contact is observed. In spite of the absence of a jump into contact, upon separation of the surfaces the total force goes through an attractive minimum.
I I I Separation (nm)
b
Separation (nm)
Figure 2-9 Some representative force-distance curves, showing the behaviour of the advancing (filled symbols) and retracting (open symbols) parts of the force curve: (a) pHz 9, hematite particle, no amine; and (b) pHz5 8, hematite particle, no amine.
Jumps into contact were often observed when the electrostatic barrier was low, as illustrated in Figure 2-9b. The data suggest that when the electrostatic force is strongly repulsive, the jump into the primary minimum can be masked by contact of asperities on the 2 surfaces. In these cases, a jump out of contact was sometimes observed and in other cases not, depending on the particle-tip combination used. An abrupt increase in repulsion resulting from contact of surface asperities generally occurred at separations ~2 nm. Thus force data from this region was excluded from the fit of Equation (l-6) to the force data.
2-7 The IEP for magnetite and hematite can be determined from measurements of the force-distance curves as a function of pH (in the absence of added amine). Since the surface potential of Inconel600 is negative over the pH range of interest, the IEP of magnetite or of hematite or of both will be the pH at which the total force switches from repulsion (i.e., positive) to attraction (i.e., negative). Figures 2-10 and 2-l 1 show the best fits of Equation (l-6) to the force-curve data for magnetite and hematite, respectively.
Separation (nm) Figure 2-10 Best fft of Equation (l-6) to the force-distance data for magnetite approaching the surface of lnconel600.
Figure 2-10 shows that the total interaction force is repulsive and increases in magnitude with decreasing separation before going through a maximum for separations of -4 to 6 nm. This result shows that surface repulsion dominates for distances greater than 4 to 6 nm, and van der Waals attraction only becomes important at smaller separations. As the distance between the surfaces is reduced from about 5 nm, the total force steadily decreases and eventually becomes attractive at a separation of -2 to 4 nm. The magnitude of the repulsive force between magnetite and Inconel600 and the height of the energy barrier decreases steadily as the pH is reduced from 10 towards 7. The total force, although very small, is still repulsive at pH= 7, indicating that the IEP for this magnetite sample is at a pH just below 7. This result is in good agreement with the electrophoresis results for magnetite shown in Figures 2-4 and 2-5. Figure 2-l 1 shows that for hematite the repulsive force drops steadily with decreasing pH but is still strongly repulsive at pH 6. Thus the IEP of this sample of hematite appears to be at a pH well below 6, which is in agreement with the electrophoresis results shown in Figure 2-6.
2-8 I 5 _;:j: 1; 5 ‘O l5 2o
Separation (nm) Figure 2-11 Best fit of Equation (l-6) to the force-distance data for hematite approaching the surface of lnconel600.
Figure 2- 12 shows the effect of morpholine at concentrations of 5 and 50 mM on the force- distance curves measured between a magnetite particle and an Inconel600 surface at the indicated pH. The force curves in the absence of added amine are also shown for comparison. In this figure. only the best fits of Equation (l-6) to the data are shown for clarity. Similar plots for ammonia. dimcthylamine and ethanolamine are shown in Appendix B of this report.
In all caves. the addition of amine reduced the magnitude of the repulsive force between the surfaces of mtignetite and Inconel600. The presence of a 5 mM solution of morpholine had ahout the s;Lmc effect on the magnitude of the repulsive force across the pH25 range 6 to 10. The 50 m>l lublulron of morpholine had about the same effect on the repulsive force as did the 5 mM one fljr pt 1:. 6 w 8. For pH25 9 and 10, however, the effect was much greater with the addition of the 50 nll\f udutwn. For pH25 2 7, despite being reduced in magnitude with the addition of morphohnc. the force hetween magnetite and Inconel600 remains repulsive at large separations. At pH:s 6. however. magnetite is close enough to its IEP that the total surface force is essentially zero for all .scp;lrarions greater than 10 nm in the presence of a 5 m.M solution of morpholine. With the addition of a 50 mM solution of morpholine, the repulsive force has essentially disappeared, and the interaction force is attractive at all distances.
Similar results, with some minor exceptions, were measured for the addition of 5 and 50 m.M solutions of ammonia, ethanolamine, and ammonia, as shown in Figures B- 1, B-2, and B-3. Like morpholine, ethanolamine was much more effective at reducing the surface potential at a concentration of 50 mM than at 5 mM.
2-9 0.06
Separation (nm) Separation (nm)
Separation (nm) Separation (nm)
0.12 pH6 / 0.08 -- !
0.04 -- ! / 4 4’ p
Separation (nm) Figure 2-12 Plots of the best fit of the force curve versus separation for the system magnetiteAnconel600 as a function of morpholine concentration, at pHz5 6 to 10. Units of the abscissa are mN/m. Upper, middle, and lower lines are for 0,5, and 50 mM amine.
Figure 2-13 shows the effect of additions of morpholine to the total force acting between the surfaces of hematite and Inconel600 at selected pH25 between 6 and 10. The force curves measured in the absence of amine are also shown for comparison. In this figure, only the best fits of Equation (l-5) to the data are shown for clarity. Similar plots for additions of ammonia, dimethylamine, and ethanolamine are shown in Appendix B of this report.
The sintered agglomerate of hematite used to collect the data for the morpholine series had an IEP near pH25 8. This result is shown by the data in Figure 2-13, where the force between hematite and Inconel600 at pH25 8 is attractive at all separations. This result is in contrast to the IEP determined from the electrophoresis measurements (see Figure 2-6), and is in contrast to the IEP determined for hematite from other AFM measurements; e.g., see Figure 2-l 1. For pI& > 8, the force between hematite and Inconel600 in Figure 2-13 is repulsive, indicating that the hematite is negatively charged. Additions of morpholine at 5 and 50 mM reduce the magnitude of the repulsive force between the 2 surfaces. At pH25 8, where the force in the absence of amine
2-10 is attractive, the addition of 5 mM morpholine results in the formation of a repulsive barrier, whereas at 50 mM morpholine the force again is attractive at all separations. This observation suggests that the 2 surfaces do not behave identically and that close to the IEP small changes in amine adsorption can produce changes in both magnitude and sign of the total force. At pH25 6 and 7, the total force is attractive at all amine concentrations, indicating that the surfaces were either uncharged or of opposite sign of charge. It was noted, however, that at p&s 6 and 7, the force curves were not well described by the van der Waals attraction alone and that a better fit could be achieved, by assuming that the Inconel600 and hematite surfaces had opposite and unequal surface charges.
0.15
Separation (nm) Separation (nm)
PH 8 PH 7 1”^”t
Separation (nm) Separation (nm)
Separation (nm) Figure 2-13 Plots of the best fit of the force curve versus separation for the system hematlte-lnconel600 as a function of morpholine concentration at pHPB 6 to 10. Units of the abscissa are mN/m. Upper, middle, and lower lines are for 0,5, and 50 mM amine.
The hematite particle used in the morpholine experiments is unique in that the IEP is close to the literature value of 8.5 (Fokkink et al., 1992). For the AFM measurements on the hematite- Inconel600 system with the other amines, however, the IEP in the absence of amine is below 6 and the force curves measured in the presence of amine are much like those measured for
2-11 magnetite. For example, the addition of ethanolamine at a concentration of 5 mM has an almost negligible effect on either the total force or the potential barrier over the range pH25 7 to 10 for the hematite-Inconel system, whereas the addition of ethanolamine at a concentration of 5OmM lowers the repulsive barrier substantially, as shown in Figure B-6. A small energy barrier is still present at pHz5 6, however, even in the presence of 50 mM ethanolamine, showing that the surface of hematite is still well above its IEP. Similar behaviour is observed for the addition of dimethylamine, shown in Figure B-7, except that the energy barrier has completely disappeared at pH25 6 with the addition of a solution of dimethylamine at a concentration of 50 n&I.
Potentials derived by fitting Equation (l-6) to the force-distance curves for magnetite and hematite are listed in Tables 2-2 and 2-3, respectively, for amine concentrations of 0, 5, and 50 mM. The sign of the surface potential was inferred from the trends in the total force and from comparison with the electrophoresis data. The potentials become increasingly negative as the pH is increased and, with the exception of the data for morpholine, show quite clearly that the IEP for this sample of magnetite is between pH25 6 and 7. Addition of amine for a given pH tends to make the surface potentials less negative, and this observation is consistent with the reduction in the total surface repulsive force measured by AIM.
Table 2-2 Surface potential of magnetite in mV, determined by fitting Equation (l-6) to the AFM force-distance data.
With the exception of the results with morpholine, the surface potentials for hematite were all negative over the pH range measured. As noted above, this observation is consistent with the electrophoresis measurements and some literature reports of the IEP for hematite. The hematite agglomerate used for the measurements with morpholine appeared to have an IEP closer to the expected value of 8.
Table 2-3 Surface potential of hematite in mV determined by fitting Equation (l-6) to the AFM force-distance data.
a - the force data for these pH values was unusable, possibly because of an air bubble in the cell
2-12 Surface charge densities for magnetite and hematite calculated from the surface potentials using Equation (l-7) are listed in Tables 2-4 and 2-5, respectively, for amine concentrations of 0,5, and 50 mM. As expected, the surface charge densities follow the same trends with pH and amine concentration as do the surface potentials.
Table 2-4 Surface charge density (mC/m*) calculated for magnetite from Equation (l-7).
Table 2-5 Surface charge density (mC/m*), calculated for hematite from Equation (l-7).
pH 1 ammonia I dimethylamine ethanolamine I morpholine I I 0 I 5 I 50 I 0 I 5 I 50 I 0 I 5 I 50 I 0 I 5 I 50 6 ( -3.0 1 5.4 1 2.1 1 -4.4 1 -a 1 -2.4 1 -4.9 1 -6.8 1 -5.1 1 0 1 0 1 0 7 1 -5.8 1 -5.8 1 -5.8 1 -4.2 1 -a 1 -3.4 1 -6.6 1 -6.4 1 -4.4 1 0 1 0 1 0 8 1 -5.8 1 -5.6 1 -5.7 1 -5.2 1 -5.3 1 -2.9 1 -7.0 1 -6.8 1 -4.4 1 0 1 -6.4 1 0 9 1 -6.3 1 -7.6 1 -7.1 1 -6.7 1 -5.8 1 -3.7 1 -8.1 1 -8.1 I -5.8 1 -7.9 I -7.6 I -4.4 10 1 -8.3 1 -8.3 1 -8.0 1 -7.9 1 -7.9 1 -5.2 1 -9.0 1 -9.0 1 -6.9 1 -9.5 1 -6.4 1 -5.9 1 a - the force data for these pH values was unusable, possibly because of an air bubble in the cell
2.4 Surface Tension
Figure 2-14 shows a photograph of the cell at 25 “C. The magnetite surface is on the right and appears dark black, whereas the Inconel 600 surface is on the left and appears gray. The photograph has been digitally filtered to enhance the meniscus. It is clear from the picture that the contact angle on Inconel 600 is larger than that on magnetite.
vapour \CI / Figure 2-14 Photograph of the interior of the cell used to measure the contact angles (0) of a morpholine solution on lnconel600 and magnetite, taken at 25°C.
2-13 In the first trials with the apparatus, condensation on the windows resulted in poor images at higher temperatures. Therefore, the contact angles were measured by placing a magnifying lens in front of the cell and tracing the meniscus onto a piece of transparent plastic. The contact angles were then measured directly from the traced images.
The results of these measurements are shown in Figure 2-15. From Figure 2-15, it appears that the contact angle at the magnetite-solution interface increases linearly over the temperature range examined. In contrast, the contact angle at the Inconel6Wsolution interface increases as the temperature is raised from 25OC to 50 “C, and then decreases linearly with increasing temperature above 50°C. The 2 surfaces have the same contact angle at about a temperature of 110°C.
90 f
2 30 E 0 20 0 ~ i l magnetite 10 0 i-600
I I 0 I I i 0 50 100 150 Temperature “C
Fw 2-15 The effect of temperature on the wetting angle of the InconelbO&solution and the magnetite+solution interfaces.
The con1;y11 ~nglc* u’crc less than 90” for both the water-Inconel600 and water-magnetite intcrfxc\ o\ cr the temperature range examined, meaning that both Inconel600 and magnetite are hydrophiilc. Magnetite appears to be less hydrophilic than Inconel600 (magnetite has a smaller contact angle) and is becoming more hydrophobic with increasing temperature. If the trend in Figure 2- 15 continues, magnetite is predicted to be hydrophobic at steam generator operating temperatures. In contrast, the surface of Inconel600 is becoming more hydrophilic with increasing temperature above 50°C.
2.5 Loop Deposition Tests
Table 2-6 shows the matrix of loop deposition tests that were performed for this investigation. Some tests were performed to extend the database for ammonia, morpholine, ethanolamine, dimethylamine, and potassium hydroxide tests to 4 runs each. Other tests were done to examine the effect of 3 additional amines (3-methoxypropylamine, pyrrolidine, and 4-aminobutanol) on
2-14 the particle deposition behaviour. Two extended deposition tests were done in which the colloidal suspension of particles was injected for a period of 24 h instead of the usual 8 h. This analysis was done to try to cover a greater fraction of the test section with particles and get some insights into the longer-term deposition behaviour. Details of the operating and chemistry conditions for each of the 24 tests performed are listed in Table C-lof Appendix C of this report.
Table 2-6 Listing of loop deposition tests performed in this investigation.
Tests with Magnetite I Number of Tests Morpholine 3 Ammonia 1 dimethylamine 2 notassium hvdroxide 2 3-Methoxypropylamine 2 Pyrrolidine 2 4-Aminobutanol 2 Tests with Hematite Number of Tests Ethanolamine 2 Dimethylamine 2 Potassium hydroxide 4 3-Methoxypropylamine 2 Figures 2-16 and 2-17 show representative plots of temperature and deposition rate as a function of mixture quality for magnetite deposition using pyrrolidine and 3-methoxypropylamine, respectively for pH control. Additional figures showing similar plots for the other loop tests identified in Table 2-6 are found in Appendix C of this report.
AECL Cbdk Rivet Laboratories. H3 Loop DO!X--Fe304+Pymlidine
3.0&03 7 "E 2 2.5B03 y" cr:% 2.WO3 z6 'Z
! "5E03 p B l.OE-03 P
5.OEAM
O.OE+co t -0.4 -0.2 0 0.2 0.4 0.6 0.8 Muture Quality [-I
Figure 2-16 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (dlabatic) test section. 0 indicates locations on the unheated (adiabatic) test section.
2-15 The figures show deposition data for several different flow and heat-transfer regimes, as well as for deposition on both heated (diabatic) and unheated (adiabatic) portions of the test section. For mixture qualities less than -0.22, the flow regime is single-phase forced convection. Deposition data for this flow regime come from both unheated and heated regions of the test section. The onset of sub-cooled nucleate boiling takes place at a mixture quality of approximately -0.22. At this point, the temperature at the wall-fluid interface is high enough to initiate bubble nucleation and growth at the wall, but the bulk temperature is still below the boiling point so that the bubbles collapse when they encounter sub-cooled fluid. This heat-transfer mode prevails, up to a mixture quality of approximately zero. At this point, the fluid has reached saturation temperature; the steam bubbles do not collapse when they leave the surface, and net steam quality is produced. This heat-transfer mode is called saturated nucleate boiling and prevails up to a steam quality of at least 0.20 (see Figure 2-21), where there is a transition to annular flow conditions. Deposition data in the saturated nucleate boiling regime come from both heated and unheated regions of the test section. The heat-transfer modes in the annular flow regime are complex, with nucleate boiling becoming less important at the expense of 2-phase forced convection, plus evaporation as the steam quality increases. Deposition data in the annular flow regime come from both heated and unheated portions of the test section. 1 AECL Chalk River Laboratories, H3 Loop D102--Fe304 + h4PA 6.OErO4 300 Axial Position on the He*ed Sections [ml -I I. -1 c 0.10 I so 2.10 2.70 4.10
A-A
-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 Mixture Quality [-I Figure 2-17 Normalized deposition rate vs. mixture quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section.
Normalized deposition rates (measured deposition rates normalized to a magnetite concentration of 10m6 kg/kg) for all deposition tests with magnetite are summarized in Table 2-7. Although features may be found that are specific to just one test or another, the following general
2-16 observations can be made based on the results in Table 2-7 and from Figures 2- 17 and 2- 18 and Figures C- 1 to C- 12 of Appendix C of this report. l The deposition rate for magnetite is lower on unheated than on heated regions of the test section. This observation is consistent with the fact that the heated regions of the test section are primarily under flow-boiling conditions (either sub-cooled or saturated nucleate boiling), where bubble nucleation and growth provides a mechanism to enhance mass transfer of fluid to the surface. The unheated sections were in either single-phase (X < -0.22) or 2-phase (X > 0) forced convection, where the mass transfer mechanism for fluid to the surface is eddy diffusion, except for X 2 0.4, where deposition is enhanced by the deposition of droplets entrained from the annular film (See Section 2.5). Thus the deposition rate is greater under flow-boiling conditions for 0 < X < 0.25 than for 2-phase forced convection at X = 0.03 and 0.25. At X = 0.5, where the deposition rate is enhanced by droplet deposition (see Section 2.5 for a discussion of the mechanism), the rate is also greater under flow-boiling conditions than for 2-phase forced convection.
Table 2-7 Summary of loop deposition results for magnetite. Details from the loop deposition results for magnetite, Fe30J Remarks Exp.ID Kp for Flow Boiling, Kp for Forced Convection, kg/m% kg/m% 0 < x < 0.25 x - 0.5 single x - 0.03 x - 0.25 x - 0.5 phase MORPHOLINE CHEMISTRY Low A, 02 DO97 4.68E-04 6.19E-03 3.37E-04 2.6OE-04 3,13E-04 1.54E-03 DlOl 2.36E-04 7.89E-04 1.21E-04 8.93E-05 1.41E-04 8.85E-04 D119 3.41E-04 9.OOE-04 6.13E-05 1.83E-04 1.57E-04 6.29E-04 AMMONIA CHEMISTRY Low A D120 8.29E-05 1.33E-04 5.18E-05 6.73E-05 3.88E-05 3.22E-04 DIMETHYLAMINE CHEMISTRY Low A DlOO 1.24E-04 9.4OE-04 l.O5E-04 3.97E-05 8.62E-05 1 .OlE-03 D105 1.21E-04 l.lOE-04 3.94E-05 6.19E-05 7.80E-05 1.02E-04 POTASSIUM HYDROXIDE CHEMISTRY ? DO98 9.99E-04 3.09E-04 5.158-04 6.87E-04 9.58E-04 1.94E-02 D103 2.62E-04 6.6OE-04 1.54E-04 2.58E-04 1.94E-04 3.47E-03 PYRROLIDINE CHEMISTRY Low A DO99 3.16E-04 8.01E-04 2.62E-04 4.08E-04 4.1 lE-04 2.30E-04 D117 8.12E-04 5.23E-04 1.81E-04 3.95E-04 2.18E-04 5.1 lE-04 3-METHOXYPROPYLAMINE CHEMISTRY Low A D102 1.46E-04 5.22E-04 l.l5E-04 9.84E-05 1.89E-04 2.57E-04 D104 6.19E-04 2.03E-04 7.56E-05 2.73E-04 4.1OE-04 7.01E-04 4-AMINOBUTANOL CHEMISTRY Low A D116 5.94E-04 5.2OE-04 2.09E-04 4.78E-04 3.39E-04 l.O3E-03 D118 3.04E-04 2.71E-04 1.91E-04 2.48E-04 1.7OE-04 1.9OE-04J Legend: “Low A”-low amine l The onset of sub-cooled nucleate boiling at about X = -0.22 results in a significant (up to IO-fold) increase in deposition rate. The rate goes through a maximum, however, at X generally between -0.15 and 0, and the rate for X > 0 is only 2 to 3 times greater than the rate
2-17 for single-phase forced convection. The maximum in the deposition rate near X = 0 was observed previously (Turner et al., 1997) but was not as pronounced as in this investigation. The difference can probably be attributed to the improved temperature control provided by the newly installed flow control valve on the loop interchanger that helps maintain stable thermohydraulic conditions along the test section. l The deposition rate increases abruptly in the annular flow region-i.e., X > 0.20-but the steam quality where this enhancement takes place is variable. Generally the rate starts to increase by X = 0.4, but in some tests there was no increase up to X = 0.5. The increase in deposition rate is postulated to be associated with droplet entrainment and re-deposition from the liquid film that wets the heat-transfer surface in annular flow, and is discussed in detail in Section 2.5 and in Appendix D of this report. The annular film must develop before droplet re-entrainment becomes significant, however, and it may be that film development is affected by subtle changes in surface roughness and loop operating conditions that affect, in turn, the steam quality at which the enhanced deposition takes place. l The deposition rates measured for pH controlled with dimethylamine are consistently lower than those measured for pH controlled with other bases, including potassium hydroxide. (The rate for ammonia in Table 2-7 appears anomalously low. (See discussion in Section 3.) Rates measured for the 3 additional amines included in this investigation-pyrrolidine, 3-methoxypropylamine, and 4-aminobutanol-were closer to the rates measured for morpholine and ethanolamine. A full discussion of these results will be presented in Section 3, where the discussion will include results of the previous investigation as well (see Turner et al., 1997).
Figures 2-18 and 2-19 show representative plots of normalized deposition rate and wall temperature as a function of mixture quality for hematite deposition with pH controlled using dimethylamine and 3-methoxypropylamine, respectively. Additional figures showing similar plots for the other hematite tests listed in Table 2-6 are found in Figures C-13 to C-20 of Appendix C of this report. Normalized deposition rates for all of the hematite tests are listed in Table 2-8. The main observations that follow from Figures 2-18,2- 19, C-l 3 to C-20 (of Appendix C of this report), and Table 2-8 are as follows: Hematite showed the same trends in normalized deposition rate with mixture quality as did magnetite. The deposition rate measured for hematite under flow-boiling conditions was significantly higher than the rate measured for magnetite, especially when oxygen was present in the loop during the hematite test. The deposition rate of hematite in the flow-boiling regime is especially sensitive to the concentration of dissolved oxygen. For the ethanolamine, dimethylamine, and potassium hydroxide tests, the hematite deposition rate in the test done without oxygen in the loop was 14.4%, 13.3%, and 10.2%, respectively, of the rate when oxygen was present. When dissolved oxygen was present, the deposition rate of hematite in the flow-boiling regime was an average of 18 times greater than the rate in single-phase forced convection. When oxygen was absent, the rate in flow-boiling conditions was only 26% higher than the rate in single-phase forced convection.
2-18 l The deposition rate was lowest when 3-methoxypropylamine was used for pH control.
AECL Chalk River Laboratories, H3 Loop DllC-Fe203 + DMA I.6502 3cO Axial P”6i”“” “” Ihc “caled .s.%ti”nS Irnl 3 + + I
T E 1.2EO2 -- B s l.OEO2 -- Y d .g 8.OE-03 -- .z % I
:o. I. I,. I.. I. -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-I
Figure 2-18 Normalized deposition rate vs. mixture quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section.
AWL Chalk River Laboratories, H3 Loop D112--Fe203 + MPA II O&O? 300
l.OE-03
O.OE+OO 150 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-] Figure 2-19 Normalized deposition rate vs. mixture quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section.
2-19 Table 2-8 Summary of loop deposition results for hematite. Details from the loop deposition results for hematite, Fez03 ELemarks Exp.ID Kp for Flow Boiling, Kp for Forced Convection, kg/m% kg/m% 0 02 Dlll 8.60E-03 1.2OE-03 9.81E-04 3.48E-04 4.38E-04 4.4OE-04 No 02 DlO8 1.24E-03 1.59E-03 7.61E-04 2.55E-03 6.72E-04 3.63E-03 DIMETHYLAMINE CHEMISTRY 02 D114 5.88E-03 1.35E-02 1.51E-04 1.87E-04 9.1 lE-04 3.14E-03 No O2 D106 7.81E-04 6.08E-04 7.44E-04 3.56E-04 3.43E-04 4.87E-04 POTASSIUM HYDROXIDE CHEMISTRY 02 D109 3.08E-03 2.73E-04 1.83E-04 2.91E-04 6.48E-04 1.5 lE-04 D113 1.77E-03 4.25E-03 1.88E-04 7.54E-04 l.O7E-03 2.79E-02 D115 4.26E-03 2.82E-03 l.l7E-04 2.58E-04 7.97E-04 1.67E-03 No O2 D107 3.09E-04 5 .WE-04 2.77E-04 1.57E-04 2.15E-04 7.22E-04 3-METHOXYPROPYLAMINE CHEMISTRY 02 DllO 6.01E-04 1.57E-04 1.64E-04 2.17E-04 1.48E-04 8.74E-05 D112 l.O7E-03 7.72E-04 1.2OE-04 1.45E-04 9.64E-05 9.32E-05 Legend: “02”-dissolved oxygen present in loop water, “No OT-no oxygen present Two of the deposition tests in this investigation, D- 119 and D-120, were conducted with the deposition phase extended by a factor of 5 to build up more deposit on the test section and investigate the effect of a tube deposit on the particle deposition rate. A plot showing the build- up of deposit on the test section as a function of time is shown in Figure 2-20. 10 Time [h] Figure 2-20 Build-up of radioactivity resulting from the deposition of magnetite onto the surface of lnconei 899 under flow-boiling conditions. The suspension of magnetite particles was traced using “Fe so that the build-up could be followed using a Tray detector, as described in Turner et al., 1997. 2-20 For tc 0 h, the on-line y-ray detector sees only residual activity on the loop surfaces from previous tests. Time 0 marks the beginning of the injection of magnetite into the loop; this event is marked by an immediate increase in the level of radioactivity measured at the test section. Magnetite then deposits onto the test section at a constant rate over the next 48 h at which point the injection was switched off, as shown in Figure 2-20. Although enough magnetite had deposited to cover the surface with a monolayer of deposit, SEM microscopy showed that the deposit formed in discrete clumps and so had not entirely covered the surface. This test shows that the injection time can be increased significantly (i.e., 5-fold) without difficulty and that the deposition rate remains linear for significant coverage of the surface. It is reasonable to assume that even higher degrees of surface coverage are possible by this method, and this assumption will be explored in subsequent work. Morphology of the deposit from various locations along the test section was routinely determined using SEM. The implications of the morphological changes with steam quality are not fully understood at this time, nor are they obviously related to differences in deposition rate from one amine to another or between magnetite and hematite. A sampling of typical deposit morphologies is included in Appendix E of this report, along with some descriptive notes for future reference. 2.6 Deposition Mechanism at High Steam Quality In the previous investigation, it was observed that the rate of particle deposition increases significantly once the steam quality is raised to a value in excess of about 0.35 (Turner et al., 1997). A detailed analysis of heat- and mass-transfer phenomena at high steam qualities and their effect on particle-fluid interactions has been conducted, and a mechanism that could account for the increase in deposition rate has been identified. Only the salient points will be discussed in this section, and a full detailed analysis is presented in Appendix D of this report. Figure 2-21 shows a schematic of the flow regimes that develop under flow-boiling conditions. Although the figure is drawn for fluid flow inside of a tube, the picture is applicable to flow on the secondary side of the tube bundle in an operating steam generator as well. At a mixture quality of - 0, the liquid reaches saturation temperature and bubbles of steam produced by vaporization at the wall are distributed throughout the liquid phase. At higher mixture qualities, steam bubbles coalesce to form ‘slugs’ of vapour, and the flow regime is called churn flow. At even higher mixture qualities there is a transition to annular flow, where the steam travels in the core of the tube while liquid travels in an annular film on the wall. In the loop tests and under typical steam generator operating conditions, the transition to annular flow takes place at a mixture quality of approximately 0.2. The liquid film thickness at the transition to annular flow is -500 pm and decreases steadily with increasing mixture quality, as shown in Figure 2-22. As a result of ‘slip’ between the steam and liquid phases, the steam travels at a progressively higher velocity than the liquid as the mixture quality increases. Whereas both phases have approximately the same velocity at a mixture quality of 0.02, Figure 2-22 shows that the steam velocity has increased to nearly 4 times the liquid velocity at a mixture quality of 0.7. 2-21 One conclusion that can be drawn from Figure 2-22 is that the liquid film velocity does not change sufficiently with increasing mixture quality to account for the abrupt increase in deposition rate that is observed at high mixture qualities, i.e., mixture qualities in excess of 0.35 (See, for example, Figure 2-17). Thus, the increase in deposition rate must be associated with the onset of an additional particle transport mechanism. In the annular flow regime, fluid instabilities cause droplets to be entrained from the surface of the liquid film. The entrained droplets travel along a straight path and re-deposit on the opposite side of the tube. It is postulated that re-deposition of entrained droplets carrying with them particles at the film concentration provides the additional transport mechanism that leads to the increased deposition rate at high mixture qualities. -X=0.60 Water Droplets- Water Film - Steam- Steam Bubbles- Water- Figure 2-21 Flow regimes under flow-boiling conditions. 2-22 8.0 600 0 0 - 7.0 -- Average Liqdi! Film Steam Velocity,’ Thickness, TO / /500 -- z 0 Entrainment’. / . a ‘;; 6.0 -- \ / 0 3 2 _. . . 0 / 0 -- 400 B \ .g 5.0 -: . . / / $j B 8 -. . *. / / b ‘ii, / ;< E > 4.0 -r 0 l . -- 300 .= z 0 l . r.& 0 -_ m ‘Z I ‘_ ‘3 d 3.0 / / -; __ -. 5. m s 0 / *. -- 200 2 l _ -. & --__ l .__ 2 Y -- 100 4 0.0 I I 1 I I I ; I I I ; I I I ; a I I I ; I 1 , ; 0 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 Mixture Quality [-] Figure 2-22 Steam-liquid velocities and film thickness vs. mixture quality. 0.5 _ -- _------0.5 -1 ,.* a* F 0.4 . ..’ Q -1 . . 5 0.4 -I Droplet Rate Depositon : .’ P : ; 0.3 -r . . 15 , ’ gt 0.3 -- . 6 . . s 0.2 -; . -z g 0.2 -; : , stopping distance > ;3”‘3 0.1 -: . film thickrk~s : 0.1 -: . : . 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 Mixture Quality [-I Figure 2-23 Calculated droplet deposition rate vs. mixture quality. 2-23 The dashed line in Figure 2-23 shows the calculated droplet deposition rate as a function of mixture quality. Not all droplets that re-deposit deliver particles to the wall of the tube. The droplets must also have sufficient momentum to coast through the liquid film to the wall. This consideration gives rise to the solid line in Figure 2-23 for droplets with stopping distance greater than the liquid film thickness, where the stopping distance is defined as the distance that a particle will travel in a fluid before its momentum is reduced to zero by the Stokes drag force (Friedlander and Johnson, 1957). For an estimated droplet diameter of 10 pm, and assuming that the droplet is rigid and is not miscible with the liquid film, the onset of increased deposition by this mechanism is calculated to occur at a mixture quality of 0.4. Despite the assumptions made for calculation of the stopping distance, this result is in good agreement with the results of the deposition tests. It is worth noting that the mechanism described above would not cause an increase in particle deposition at the wall if the droplets coalesced with the liquid in the film before they had time to coast to the wall. One could presume that a reduction in either the surface tension or elasticity of the liquid droplets would tend to increase the rate of coalescence and consequently reduce the rate of deposition in the annular flow regime. Dispersants are surface-active reagents that have the property of reducing the surface tension of the air-water interface. High-temperature loop tests with dispersants have shown both a reduction in wall superheat (related to surface tension at the steam-water interface) and a reduction in deposition under flow-boiling conditions at low steam quality (Balakrishnan et al.,1998; Burgmayer et al., 1998), which suggests that they might prove useful for reducing deposition at high steam quality as well. 2-24 3. DISCUSSION The following observations were made in our previous investigation (Turner et al., 1997): l The deposition rate for hematite was higher than the rate for magnetite. l The deposition rate for magnetite increased with increasing amine concentration (at constant pH. Excess amine was neutralized by acidic contaminant in the cover gas), l The deposition rate for magnetite decreased with increasing room temperature base strength of the amine. l The deposition rate for hematite decreased towards that of magnetite as the loop water became less oxidizing. These observations were taken as evidence for the importance of surface chemistry in governing the deposition rate of corrosion products under steam generator operating conditions. The difference between the deposition rates of hematite and magnetite was attributed to the difference in sign between their respective surface potentials at pHr = 6.2 and temperature = 270°C. For example, magnetite- which is predicted to be negatively charged under steam generator operating conditions (Shoonen, 1994)-will be repelled by the negatively charged surface of Inconel600, whereas hematite-which is predicted to be positively charged under the same conditions-will be attracted. This difference was proposed to account for the nearly lo-fold difference in the deposition rates between the 2 oxides. The effect of concentration and base strength of the amine on the deposition rate of magnetite was hypothesized to be related to adsorption of amine onto the surface of the corrosion product. The reasoning was that the amine added for pH control exists in solution in both the neutral and protonated form: HA+ w A+H+ (3-l) It was suggested that adsorption of the protonated amine onto the negatively charged surface of magnetite would reduce the repulsion between the surfaces of magnetite and Inconel600 and, consequently, increase the rate of deposition. Thus greater adsorption of amine onto the corrosion products is predicted to correlate with a higher rate of deposition. Evaluation and testing of this hypothesis formed the basis for the present investigation. If, indeed, adsorption of amine onto the corrosion products and the effect this adsorption has on surface potential has a marked effect on deposition behaviour, then this hypothesis provides a strong incentive to determine the properties of the amine that most affect its adsorption so that these properties can be optimized when selecting the amine for pH control in the feedwater circuit. Each of the 4 amines tested showed a strong tendency to adsorb onto both magnetite and hematite at room temperature, as shown by the results in Section 2.1, with the amount adsorbed increasing in proportion to the concentration of amine in solution. Since the concentration of amine required to achieve a fixed pH increases with decreasing base strength, the amount of amine adsorbed onto the corrosion products will increase as the base strength of the amine 3-l decreases. A second factor that is expected to contribute to the amount adsorbed is the size of the amine molecule, or its “footprint” on the surface of the corrosion product. The results in Section 2.1 show that the amount of amine adsorbed per unit surface area of corrosion product increases with decreasing molecular size for a given concentration of amine. Thus, if our hypothesis is correct, a weaker base and smaller amine molecule should correlate with greater 25OC, included in this part of the investigation. mM,between 5 and 50 concentrationpH, of amine. The amount of amine required to achieve a particular expectpH. dimethylamine to be adsorbed the least for a given pHgreater extent than dimethylamine for a given pH. Table 3-1 Comparison of trends in amine base strength, molecular size, and the relative amount mM concentrations of amine. Relative Ranking Base Strength Molecular Size Amount Adsorbed 5mM 50 mM Highest dimethylamine morpholine ammonia ammonia ethanolamine ethanolamine dimethylamine dimethylamine ammonia dimethylamine ethanolamine morpholine Lowest morpholine ammonia morpholine ethanolamine The effect of the adsorption of amine on the surface potential of the corrosion products is shown quite clearly by the results of both electrophoresis and AFM. The theory of electrophoresis predicts that adsorption of a cationic (positively charged) species will shift the IEP of an oxide towards higher pH (Hunter, 1981). Thus the results of electrophoresis show that the addition of amine to suspensions of both magnetite and hematite resulted in the adsorption of a cationic species, which is presumed to be the protonated amine. The shift in IEP towards higher pH means that the surface potential of the corrosion products has been reduced to less-negative values with the addition of amine. Hematite showed both a greater tendency to adsorb amine and a larger shift in IEP for a given amine concentration than did magnetite. It is not clear why this should be the case, but the 2 trends are qualitatively consistent. The AFM results are remarkably consistent with those from electrophoresis, even to the extent that the magnitude of the surface potentials for magnetite and hematite determined by both 3-2 methods in the absence of amine are in good agreement. Atomic force microscopy not only shows that adsorption of amine reduces the magnitude of the surface potentials, it also provides a quantitative measure of how adsorption affects the total interaction potential between the corrosion products and Inconel600. When there is a strong force of repulsion between the corrosion product and Inconel600, the total interaction force between the 2 surfaces in question goes through a maximum. The energy required for a particle in a flowing suspension to surmount this force barrier and deposit on the surface can be calculated by integrating the force from infinite separation (in practice, the integration can start at a separation of about 40 nm, where the force is essentially zero) to the separation corresponding to the maximum force. This calculation shows that a 0.25pm magnetite particle would require an energy of 12 kT at 25°C to surmount a force barrier of height 0.04 mN/m, where kT is the average thermal energy of the particle in a stagnant solution in thermal equilibrium with its surroundings. In the absence of amine, the force barrier at pH 10 between the corrosion product and the surface of Inconel600 reached from 0.1 to 0.2 mN/m, corresponding to energy barriers for a 0.25#m particle between 30 and 60 kT. An energy barrier of this magnitude would be expected to significantly reduce the rate of particle deposition from a flowing suspension. Both a reduction in pH and the addition of amine effectively reduced the magnitude of this force barrier, in each case by reducing the magnitude of the surface potentials. For example, Figure 2-12 shows that a reduction in pH from 10 to 7 and the addition of 50 mM morpholine at pH 10 are equally effective at reducing the height of the force barrier to 0.01 mN/m, which corresponds to a barrier of 3kT at 25°C. The results in Tables 2-3 and 2-5 show that the addition of amine generally made the surfaces of hematite and magnetite less negative. This reduction in the magnitude of the surface potential is attributed to adsorption of the protonated amine, HA+. The corresponding reduction in the magnitude of the surface charge density was most pronounced with dimethylamine, presumably because it has the highest base strength of the amines tested and, therefore, produces the highest concentration of HA+ in solution. The average change in surface charge density for all amines evaluated at a concentration of 50 mM and pH 10 was about 3 mC/m* (see Tables B-l and B-2 of Appendix B of this report). This change can be compared to the change in surface charge density predicted from the adsorption isotherms, but first we must consider what could happen when a charged species is adsorbed onto the surface of a metal oxide. A metal oxide acquires a surface charge when exposed to water via reactions of the following sort: -M-OH + II+ a -MOH2+ (3-2) -M-OH + OH- e -MO- + H20 (3-3) The net surface charge density is given by the difference in the concentration of -MO&+ sites and -MO- sites on the surface, and will be a function of both the pH and the magnitudes of the equilibrium constants for Reactions (3-2) and (3-3). The pH at which the net surface charge is zero is called the point of zero charge (PZC). For pH > PZC there is an excess of negative charge on the surface of the metal oxide, and for pH < PZC, an excess of positive charge. 3-3 Two limiting cases will be considered for the adsorption of a cation (such as a protonated amine, HA+) onto the surface of a metal oxide at a pH > PZC, i.e., where the surface is negatively charged. One limiting case is for the surface to respond to the adsorption of an HA+ by releasing an H+ cation into solution. In this case, the surface charge and surface potential will remain unaltered by the adsorption of a protonated amine; the adsorbed cation simply shifts the equilibrium in Reactions (3-2) and (3-3) so that one cation (HA+) is exchanged for another (H’) . The second limiting case to be considered is that the adsorption of a protonated amine does not affect the equilibrium between the surface species -MOH2+ and -MO- . In this case adsorption of each protonated amine neutralizes 1 negative charge on the surface of the metal oxide. Calculations show that the reduction in the magnitude of the surface charge density with the adsorption of amine is significantly lower than that predicted by this second limiting case; that is, the reduction in the surface charge density appears to be significantly less than one charge neutralized per adsorption of a protonated amine. The results are listed in Table 3-2 for an amine concentration of 50 mM and pH 10. Table 3-2 Calculated change in surface charge density with adsorption of amine for the second limiting case. Amine Surface Charge Density (C/m’) Surface Charge Density (C/m’) Magnetite Hematite Morpholine 1.5 2.9 Ammonia 65 49 Ethanolamine 7.4 30 Dimethylamine 71 274 For this analysis, the concentration of protonated amine on the surface was calculated from the total amount of amine adsorbed with the assumption that the dissociation constant of the amine on the surface is the same as for the amine dissolved in solution. The changes in surface charge density predicted for the second limiting case are significantly greater than those determined from the AFM results (see Tables 2-4 and 2-5), for which the surface charge density on magnetite and hematite changed by only 3 mC/m* with the adsorption of amine from a 50 mM solution at pH 10. This value corresponds to a change of about 1 excess charge per 50 nm*. Thus the effect of the adsorption of amine on the surface charge density cannot be estimated using the simplifying assumption described for the second limiting case. In addition to the likelihood that adsorption of a charged species does shift the equilibria in Reactions (3-2) and (3-3), the assumption that the dissociation constant remains the same for both dissolved and adsorbed amine molecules is likely flawed as well. Adsorption onto a surface (especially multilayer adsorption, as we appear to have in this case) will bring the amine molecules into much closer proximity to one another than is the case for molecules dissolved in solution. Protonation of the adsorbed amine molecule will, thus, be inhibited by the Coulomb repulsion between adjacent charged species, which will tend to reduce the magnitude of the dissociation constant for adsorbed amine. To compare the effect of adsorption of amine at 25°C with the deposition behaviour of the corrosion products at 270°C, the discussion will also include results from the previous investigation (Turner et al., 1997). Tables 3-3 summarizes the deposition results for magnetite 3-4 from both investigations, where the results of the current investigation are shown in bold type. Only average deposition rates are listed; rates for individual tests are listed in Table C-2 of Appendix C of this report. Table 3-3 shows clearly that under flow-boiling conditions the deposition rate of magnetite increases with increasing amine concentration at constant pH. (Recall that an acidic impurity in the cover gas was acting to neutralize some of the amine so that higher concentrations were required to achieve the target pH, as discussed in Turner et al. (1997). Lower amine concentrations were needed once a “scrubber” was installed on the cover gas line.) The dependence of the deposition rate on amine concentration correlates well with the adsorption and AFM measurements, which show that the adsorption of amine and consequent reduction of the surface charge on magnetite increases with increasing concentration of amine. Reduction of the surface charge on magnetite lowers the force of repulsion between the surfaces of magnetite and Inconel 600 which, in turn, results in an increase in deposition rate. Table 3-3 Summary of deposition results for magnetite. Results of the current investigation are shown in bold, and the other results are from Turner et al. (1997). r Summary of all Ii3 loop deposition results for magnetite, FeJOd 1 Imine Remarks # of exp. Cp for Flow Boiling, kg/m% Kp for Forced Convection, kg/m% for 0 < X < 0.25 at X - 0.5 at single at X - 0.03 at X - 0.25 at X - 0: phase vIorph High A 2 1.64E-03 Low A 3 3.483-04 2.633-03 1.73E-04 1.773-04 2.043-04 l.O2E-03 3TA High A 2 l.O6E-03 Lou A 3 5.52E-04 6.65E-03 5.46E-04 Etched 2 2.53E-03 Surface IJ,U A. SP 2 l.O7E-04 (H1 Hlph A 2 8.95E-04 Low A 1 8.293-05 1.333-04 5.183-05 6.733-05 3.883-05 3.223-04 IMA tilgh A 4 6.17E-04 Il,U A 5 l.l6E-04 6.96E-04 7.2OE-05 5.08E-05 9.61E-05 5.58E-04 KOH , 2 6.303-04 4X3-04 3.343-04 4.733-04 5.763-04 l.l4E-02 IA,- A 2 1.71E-04 2.23E-03 1.51E-04 3 PYn km-a A 5.643-04 6.623-04 2.223-04 4.023-04 3.153-04 3.703-04 MPA IAN A 2 3.833-04 3.62E-04 9.543-05 1.863-04 2.993-04 4.793-04 IAB Low A 2 4.493-04 3.953-04 2.OOE-04 3.633-04 2.553-04 6.11E-04 Legend: “Low A”-low amine, “Hi All-high amine. The new results (of the current program) are in bold type. The effect of the adsorption of amine on the deposition rate of magnetite under flow-boiling conditions is further illustrated by the results listed in Table 3-4. The surface coverages of amine on the magnetite particles at 25°C for high and low amine concentrations were determined from the adsorption isotherms shown in Figure 2-l using the average amine concentrations in the slurry addition tank (see Table C-l and Table C-l found in Turner et al. (1997)). For each of the four amines, the results in Table 3-4 show a clear trend of deposition rate increasing with increasing surface coverage of magnetite by the amine molecules. This trend correlates well with 3-5 the reduction in surface repulsion between magnetite and Inconel600 with increasing concentration of amine as measured by AFM, and supports the hypothesis that adsorption of amine onto the surface of the magnetite particles at 25°C is responsible for the increase in deposition rate under flow-boiling conditions at 270°C. Table 3-4: Relationship between surface coverage of amine and the average magnetite deposition rate under flow-boiling conditions. High Amine I 31 I 145 Dimethylamine Low Amine I 0.20 I 4.8 o.12x1o-3 High Amine I 0.62~10” *: Result from a single loop test. The justification for using the low-temperature adsorption data to correlate the deposition rates measured at 270°C is that the particles spend only a few seconds in the high-temperature region of the loop during a run before entering the test section, whereas they spend several days equilibrating with the amine at 25°C before the start of each test. The fact that the electrophoresis data, which were obtained after a 24 h equilibration time, gave similar values for the surface potential as those obtained by AFM after only 1 h equilibration suggests that the latter time period is sufficient for both the adsorption of amine and the subsequent rearrangement of surface charge to have reached steady-state. Although Figure 2-3 shows that the amine desorbs with increasing temperature, the time taken to heat the cell for these measurements was long compared to the residence time of the particles in the high-temperature section of the loop. Thus the data in Figure 2-3 provide no information on the kinetics of desorption that can be applied to the loop test. Although the adsorption behaviour of pyrrolidine, 3-methoxypropylamine, and 4-aminobutanol was not measured in this investigation, on the basis of base strength alone one would predict the following trend in magnetite deposition rate with amine: 3-methoxypropylamine > pyrrolidine. Moreover, one would expect the rate with pyrrolidine to be comparable to the rate with dimethylamine since they have equivalent base strengths at 25°C. are indeed greater than the rate with dimethylamine, but the rate with pyrrolidine appears a little high. The adsorption needs to be measured, however, before drawing any conclusions. 3-6 A summary of the deposition results for hematite particles is shown in Table 3-5 for both the previous and current investigations, with the results of the current investigation shown in bold type. Only average deposition rates are listed; rates for individual tests are listed in Table C-3 of Appendix C of this report. Table 3-5 Summary of deposition results for hematite. Results of the current investigation are shown in bold, and the other results are from Turner et al., 1997. Summary of all H3 loop deposition results for hematite, Fe& I Kp for Flow Boiling, Kp for Forced Convection, kg/m% kg/m% forOcXc at X - 0.5 at single at X - 0.03 at X - 0.25 at X - 0.5 0.25 phase Morph 02 1.82E-02 ETA 02 l.O8E-02 1.2OE-03 9.81E-04 3.48E-04 4.38E-04 4.40E-04 No O2 8.53E-04 1.37E-02 6.24E-04 NH3 02 1.998-02 DMA 02 3.29E-03 3.01E-02 1.79E-03 No O2 7.813-04 6.083-04 7.443-04 3.563-04 3.433-04 4.873-04 KOH 02 3.043-03 2.453-03 1.633-04 4.343-04 8.383-04 9.923-03 No O2 3.093-04 5.093-04 2.773-04 1.573-04 2.153-M 7.223-04 MPA 02 8.363-04 4.643-04 1.423-04 1.81E-04 1.223-04 9.033-05 Legend: “O;‘-oxygen present, “No 02”-no oxygen present. The new results (of the current program) are in bold type. The deposition behaviour of hematite appears complex. There is a clear correlation between the deposition rate of hematite and the amount of dissolved oxygen in the loop, with the deposition rate increasing with increasing concentration of dissolved oxygen. A commercially available hematite was used for these tests which had an IEP near pH25 3. In contrast, hematite synthesized by the hydrolysis of Fe(III) solutions (Matijevic and Schneiner, 1978; Fokkink et al., 1992) is reported to have an IEP near pH25 8.5. Shoonen (1994) predicted that the IEP of hematite synthesized by the hydrolysis of Fe(II1) solutions will drop from pH 8.5 to 7.5 when the temperature is raised from 25°C to 270°C. Thus the latter hematite is predicted to be positively charged at pHr= 6.2 (since pHr < IEP). If positively charged, there will be no repulsive force between the hematite and Inconel600 to impede deposition, and the deposition rate would be expected to be significantly higher than for magnetite. With decreasing concentration of dissolved oxygen, the deposition rate of the commercially available hematite decreased towards that of magnetite at 270°C. Thus the deposition behaviour of hematite tended towards that of a negatively-charged particle at lower oxygen concentration and tended towards that of a positively-charged particle at higher oxygen concentration. Although the hematite had a lower IEP at 25°C than expected, it also showed a stronger tendency to adsorb amine than did magnetite and the response in the IEP to the adsorption of amine was also much greater (see Figure 2-6). Additional work to determine the effect of amine adsorption, temperature, and oxygen concentration on the IEP of hematite is required before the observed high-temperature deposition behaviour of hematite can be fully understood. 3-7 Deposition rates measured as a function of steam quality show that the enhancement to the deposition rate caused by boiling is most effective in sub-cooled nucleate boiling (where the steam bubbles collapse before leaving the surface) and in annular flow at relatively high steam qualities, e.g., X typically > 0.35. The implications with respect to the mechanisms governing the deposition and removal of particles at the heat-transfer surface is beyond the scope of this investigation. It is instructive, however, to compare the deposition rate measured as a function of steam quality with the deposit distribution on tubes removed from once-through steam generators, as shown in Figure 3-l. The measured deposit loadings follow the same general trend as measured in the H3 loop tests up to steam quality of 0.55. There are no H3 loop data to compare with the measured deposit loadings at Oconee-1 (Sykes and Sherbume, 1997) and Oconee-3 (P.L. Frattini, EPRI, private communication, 1998) for higher steam qualities. It is worth noting, however, that the plateau between steam qualities of 0.5 and 0.7 followed by a decrease in deposit loading at higher steam quality is consistent with the trend predicted by the deposition model for annular flow presented in Figure 2-23. F 0.25 5 0.20 ZI 0 Oconee-3 J 0.15 .Z W g 0.10 Q) p 0.05 0 0.2 0.4 0.6 0.8 Steam Quality Figure 3-l Comparison of typical deposition behaviour versus steam quality from the H-3 loop tests with deposit loadings measured on tubes pulled from Oconee-1 and Oconee-3. 3-8 4. SUMMARY AND CONCLUSIONS This work has demonstrated a clear link between the adsorption of amine onto the surface of corrosion products and a reduction in the force of repulsion between those corrosion products and the surface of Inconel600. Factors that lead to more adsorption of amine-e.g., higher amine concentration or a smaller amine molecule that covers less of the surface-result in a lower force of repulsion between the corrosion product and the surface of Inconel600. There is a good correlation between the adsorption behaviour measured at 25°C and the average deposition rate for magnetite particles measured at high temperature (flow-boiling conditions; 0 < X < 0.29, as illustrated in Figure 4-l (taken from Table 3-4; the result for high surface coverage by ammonia was not included in the figure for clarity). Low adsorption correlates with low deposition rate and vice versa. Hematite deposition rates are sensitive to the level of dissolved oxygen in the loop, suggesting that its surface composition and surface potential are both functions of the oxidation potential of the water. As a general rule, the deposition rate of hematite tends towards that of magnetite as the concentration of dissolved oxygen in the loop decreases. Q) 1.8E-03 z a 1.6E-03 -- I 5 1.4E-03 -- Egz 1.2E-03 -- 8% l.OE-03 -- g 38.0E-04 -- - 6.OE-04 --” n ti =ii 4.OE-04 --. ‘0 2.OE-04 -- z O.OE+OO 1II 0 100 200 300 Surface Coverage (molecules/rim*) Figure 4-1 Effect of surface coverage of amine on the average deposition rate of magnetite under flow-boiling conditions. A simple method for measuring the wetting angle at solid-liquid interfaces as a function of temperature has been identified and tested up to 140°C. The results indicate that the magnetite- solution interface is becoming increasingly hydrophobic (i.e., increasingly non-wetting) and the Inconel600-solution interface increasingly hydrophilic (i.e., more easily wetted) as the temperature is raised. This apparatus could be used to probe the relationship between wetting angle (itself a function of surface tension) and the deposition behaviour of corrosion products. This investigation has established a test protocol that can be used to evaluate the deposit-control properties of amines or other chemicals added to adjust water chemistry. The test protocol includes three, and possibly four, components: 4-l l Screen the amines for adsorption onto magnetite and select one that adsorbs the least. l Qualify the choice of amine by measuring the effect of adsorption on the magnetite-Inconel 600 interaction using APM. l Perform final validation with loop tests to quantify the effect of adsorption on the deposition rate. A new particle deposition mechanism has been identified that is operable at high mixture qualities and appears to account for the enhanced deposition rate reported for mixture qualities greater than 0.35. The enhanced deposition rate is associated with the transport of liquid droplets carrying corrosion product through the liquid film that wets the tube surface in the annular flow regime. Only those droplets that strike the liquid film with sufficient inertia are able to penetrate it and contribute to deposition at the tube surface. Modification of some property of the liquid- steam interface, such as surface tension or elasticity, may act to reduce the deposition rate at these high mixture qualities. This mechanism leads to a fourth component that, if valid, could be added to the test protocol. l Measure the effect of the amine (modified perhaps with a dispersant) on the surface tension of the steam-water interface. The effect of the modified amine on surface tension could be assessed by a measurement of the wetting angle (i.e., hydrophobicity) of the solid/solution interface, or by measuring the effect of the modified amine on the wall superheat under flow-boiling conditions. 4-2 5. IMPLICATIONS FOR CONTROLLING TUBE-BUNDLE FOULING This work has identified 2 trends in the deposition rate of corrosion products with water chemistry. These trends are illustrated in the bar graph shown in Figure 5- 1. l Magnetite deposition rate decreases with decreasing adsorption of amine. l Hematite deposition rate decreases with decreasing dissolved oxygen concentration in the presence of a reducing agent. These trends result in 2 criteria to ensure the lowest possible deposition rate of corrosion products onto the tube bundle. They are: l Minimize the concentration of dissolved oxygen in the feedwater l Select an amine for pH control that shows the least adsorption onto magnetite The criterion to select an amine for pH control that will result in the lowest deposition rate for magnetite on the tube bundle become: l Select an amine for pH control that has high base strength (to reduce the concentration of amine required to achieve the target pHr) l Select an amine with a large “footprint” on the surface of magnetite (to reduce the amount of adsorption for a given concentration of amine) One final criteria for controlling tube-bundle deposition that comes from the high-steam quality deposition results is as follows: l The amine should reduce the surface tension or elasticity of the steam-water interface (to prevent enhanced deposition at high mixture qualities). The last criterion needs to be evaluated further but it is supported by deposition results with dispersants that show a reduction in deposition rate with some dispersants that also show a reduction in wall superheat, which is a function of surface tension (Balakrishnan et al., 1998). 5-l W magnetite, high amine Cl hematite, no 02 gnetite, high amine magnetite, low amine Amine Figure 5-l Trends in magnetite and hematite deposition rate with water chemistry under flow-boiling conditions. 5-2 6. REFERENCES Balakrishnan, P.V., S.J. Klimas, L. LCpine, and C.W. Turner (1998). “Polymeric Dispersants for Control of Steam Generator Fouling”, 3rd International Steam Generator and Heat Exchanger Conference, June 21-24, 1998, Toronto, Canada. Burgmayer, P.R., R. Crovetto, S.J. Klimas, and C.W. Turner (1998). “Effectiveness of Selected Dispersants on Magnetite Particle Deposition on Simulated PWR Heat Transfer Surfaces”, 3rd International Steam Generator and Heat Exchanger Conference, June 2 l-24, 1998, Toronto, Canada. Brunauer, S., L.S. Emmett, and E. Teller (1938), J. Am. Chem. Sot. 60,309. Ducker, W.A., J.T. Senden, and R.M. Pashley (1991). “Direct Measurements of Colloidal Forces Using an Atomic Force Microscope”, Nature 353,238. Fokkink, L.G.J., A. De Keizer, and J. Lyklema (1989). “Temperature Dependence of the Electrical Double Layer on Oxides: Rutile and Hematite”, J. Colloid and Interface Sci. 127, 116. Friedlander, S.K., and H.F. Johnstone (1957). “Deposition of Suspended Particles from Turbulent Gas Streams”, Ind. and Eng. Chem. 49, 115 1. Hiemenz, P.C. (1977) Principles of Colloid and Interface Science, Marcel Dekker, Inc., New York. Hunter, R.J. (198 1). Zeta Potential in Colloid Science, Academic Press, New York. Jayaweera P., S. Hettiarachchi, and B.G. Pound (1992). “Identifying Prospective Antifouling coatings for Venturis”, Electric Power Research Institute Report EPRI TR-101256. Matijevic, E. and P.Schneiner (1978). “Ferric Hydrous Oxide Sols 3. Preparation of Uniform Particles by Hydrolysis of Fe (III)“, J. Colloid. Interface Sci.63,509-524. Schoonen, M.A.A.( 1994). “Calculation of the Point of Zero Charge of Metal Oxides between 0 and 350°C”, Geochimica et Cosmochimica Acta, 58,2845. Sugimoto, T. and E. Matijevic (1980). “Formation of Uniform Magnetite Particles by Crystallization from Ferrous Hydroxide Gels”, J. Colloid and Interface Sci. 74,227. Sykes, L.J. and P.A. Sherbume (1997). “Analysis of Steam Generator Tubing from Oconee Unit 1 Nuclear Station”. Electric Power Research Institute EPRI TR-106484. Tewari, P.H. and McLean, A.W. (1972). “Temperature Dependence of Point of Zero Charge of Alumina and Magnetite, J. of Colloid and Interface Sci. 40,267. Turner, C.W., S.J. Klimas, and M.G. Brideau (1997). “The Effect of Alternative Amines on the Rate of Boiler Tube Fouling”. Electric Power Research Institute Report EPRI TR 108004 . Atomic Energy of Canada Ltd. Report, AECL-11848 (1997). Vold R.D. and M.J. Vold (1983). Colloid and Integace Chemistry, Addison and Wesley Publishing Company, Inc., London. 6-l 7. NOMENCLATURE D= dielectric constant H= Hamaker constant (J) T= temperature (K) W= energy (J rnm2) x= quality of 2-phase mixture unit of electric charge (C ;I separation between charged surfaces in AFM measurements (m) k= Bolztmann constant (J molecule-’ K-l) no = number density of ions in solution (mm3) U = electrophoretic mobility (m2 V’ s-l) Z = ionic valence Eo= permittivity of free space (8.854 x lo-l2 F m-l) K = diffuse layer decay constant (nil) CL= dynamic viscosity (kg m’ s-l) surface charge density (C m2) ;I zeta potential (V) YO' surface potential (V) 8= contact angle (“) 7-1 APPENDIX A Amine Adsorption Isotherms on Magnetite and Hematite 1.2E+05 2.OE+04 1 .OE+05 y= 116.77x z-9 .g 1.5E+04 ‘z 8.OE+04 (u $ z 6.OE+04 g l.OE+04 5 s 5 4.OE+04 E a $ 5.OE+03 2.OE+04 O.OE+OO O.OE+OO 0 200 400 600 800 1000 0 200 400 600 800 1000 [Dimethylamine] (mM) [Ammonia] (mM) 2.5E+04 4.OE+04 , , y = 37.657x ). 2.OE+04 __ y = 22.523x R’ = 0.9998 .g 3.OE+04 .z s 1.5E+04 I ‘i ._ g 2.OE+04 E 1 OE+04 s E Q d 1.OE+04 a 5OE*03 0 OE l Oo O.OE+OO 0 200 400 600 800 1000 0 200 400 600 800 1000 [Ethanolamine] (mbt) [Morpholine] (mM) Figure A-1 Raman intensity versus amine concentration for dimethylamine, ammonia, ethanok&a. and morpholine. Linear fits to the data constrained to go through the origin are shown. The intensity of the Raman scattering increased in linear proportion to the concentration of amine, as shown in Figure A-l. Thus: I=JC, (A-1) where J is the molar scattering coefficient, and C is the molar concentration. To normalize the spectra at different amine concentrations, the water band at 1640 cm’ was used as an internal standard. The intensity of the band at 1640 cm-’ was measured for each amine concentration and a scaling factor Fs was calculated using A-l I” FBd=-, (A-2) I,” where I”‘rm is the intensity of the water band in the spectrum containing 1000 mM amine and I?‘c is the intensity of the water band in the spectrum for concentrations of 1, 10 or 100 mM amine. The intensities of the selected CH stretching mode were then scaled by En: ICHC,, = FBdCHC . (A-3) A plot of IcHc,s versus concentration gives the value of J for that amine. To normalize the spectra in the presence and absence of oxide, the water band near 1640 cm’ was again used. The spectrum of the water region of the sample in the presence of oxide, S”,c, was subtracted from the spectrum of the water region of the sample in the absence of oxide, S”,f: S”‘dif = F,. S”‘Ef - S”‘oc . (A-4) The subtraction factor, F,, was adjusted until the difference spectrum SW&f was zero over the spectral region of the water band. F, was then used to scale the spectrum of the CH stretching region of the sample without magnetite, and then the spectrum of the CH stretching region with magnetite was subtracted: SCH dif = F,* SCH,f - SCHox . (A-5) The intensity of the CH stretching bands in the difference spectrum, JcHdif , was then measured, and the concentration of amine removed from solution calculated using C, = J.IcHdif. (A-6) The adsorbed amount ca, as g amine adsorbed/g oxide, is calculated from (A-7) where V is the volume of solution used, MW is the molecular weight of the amine, and m is the mass of oxide particles used. The number of adsorbed molecules per nm2, Cm, is related to c, by c, - N, * 1x10-‘* cm = (A-8) MW.A, ’ where NA is Avogadro’s number and A, is the surface area of the oxide, as measured by the Brunauer-Emmett-Teller (BET) method (Brunauer et al., 1938). REFERENCES Brunauer, S., L.S. Emmett, and E. Teller (1938). J. Am. Chem. Sot. 60,309. A-2 APPENDIX B FORCE-DISTANCE CURVES FROM NANOSCOPE II RAW FORCE DATA A typical raw force curve measured by the Nanoscope II used in this work is shown in Figure B-l. 683.01 mu/d i u ...... : : : : : : : i : : : : : : : ./ . . . . [ . . . . i . . . . i . . . . i . . . . i . . . . j . . . . :..&roForceRegion . ..j . . i... 0 ...... : : : 1 : : : : : : : : : : : : : 1; : : : : : : : : : : : : : : : ...... : : : : : : : : : : : : : : : : : : : : : : : : : :. : : : : : : : : : : : ...... u ...... : :. :. :.. :.. :.. :.. :. :. . :. . : . : . : . : . : . : . : . : . : .. 0 7.55 nmidiu Figure B-l Typical raw data output from atomic force microscopy (AFM). Regions of zero force and of constant compliance are indicated. The Nanoscope II used in this work contained no software function to store the force data measured by the machine in a form such as an ASCII x-y pair, which could be directly imported into a spreadsheet or plotting program. The steps used to convert the Nanoscope II force output into a useable form are described below. The data were captured as a screen dump into a file labelled filename.scr.3 Using the program Nano2pst.exe, supplied with the Nanoscope II, this screen file was converted to a TIF file labelled filename.tif. This TIF file was then cropped to remove unnecessary white space and labels using Core1 PhotoPaint 7 and stored as a PCX format file called filename.pcx. The file “filename.pcx” was loaded into Un-Scan-it Version 3 (Silk Scientific Corporation), was digitized, and was stored as a text file named filename.prn. The text file was imported into Microsoft Excel Version 7.0a, and the raw force data were converted into a force-distance curve. The text file consists of X-Y pairs, where the X values are the position of the piezoelectric crystal on which the Inconel600 surface is mounted, and the Y 3 File names were always of the form yymmddxx, e.g., 98j12901. The numbers xx were incremented by one for each force curve stored, starting with 01. B-l values are the cantilever deflection signal. By plotting the X-Y values and taking the slope of the linear part of the force curve (labelled region of constant compliance in Figure B-l) the sensitivity SENS is obtained. The cantilever deflection, DEFLEC, is obtained from the raw cantilever data, Y, by DEFLEC = Y/SENS . (B-1) The separation, h, is then calculated from the raw piezoelectric position data, X, by h = X + DEFLEC + OFFSET . (B-2) Since the AFM does not directly give the zero of separation, the location of zero separation was taken to be the intersection of the best straight line through the constant compliance part of the force curve and the best straight line through zero force part of the curve. The term OFFSET in the above equation corrects the separation to this calculated zero separation. The force F at each value of separation was then calculated by F = DEFLEC * k, (B-3) where k is the spring constant of the cantilever. B-2 Best Fits of Equation (l-6) to Force-Distance Data for the Magnetite-Water-InconeI600 and Hematite-Water-Inconel600 Systems 0.2 0.2 tn 0 pH10 17 0.15 0.1 0.05 0 -0.05 Separation (run) Separation (nm) 0.2 0.2 -- PH7 t 5 PHS I 0.15 -- 0.1 -- 0.05 -- 0,5,50 0 I 0 20 L -0.05 I Separation (nm) Separation (nm) PHI Separation (nm) Figure B-2 Fits of F/r versus separation for the system magnetiteAnconel600 as a function of ammonia concentration for pH = 6 to 10. The concentration of added amine is indicated in units of mM. Units for F/r are mN/m. Energy required by a l-pm particle to surmount a force barrier of 0.04 mN/m is 49kT. B-3 0.08 0.08 Separation (nm) Separation (nm) -0.04 I Separation (nm) Separation (nm) Separation (nm) Figure B-3 Fits of F/r versus separation for the system magnetite/-nconel600 as a function of ethanolamine concentration for pH = 6 to 10. The concentration of added amine is indicated in units of mM. Units for F/r are mN/m. Energy required by a l-pm particle to surmount a force barrier of 0.04 mN/m is 49kT. B-4 0.16 0.12 0.08 Separation (nm) Separation (nm) 0.16 0.16 PHI PH7 0.12 0.08 0 0.08 I I Separation (nm) I Separation (nm) 0.08 t Separation (nm) Figure B-4 Fits of F/r versus separation for the system magnetiteAnconel600 as a function of dimethylamine concentration for pH = 6 to 10. The concentration of added amine is indicated in units of mM. Units for F/r are mN/m. Energy required by a l-pm particle to surmount a force barrier of 0.04 mN/m is 49kT. B-5 0.3 , 0.3 OmM pH10 PH9 0,5mM 0.15 0 -0.15 I( -0.15 Separation (nm) Separation (nm) 0.3 0.3 PH8 PH7 0.15 0.15 0,5,50 mM 0 0 I 1 10 20 30 -0.15 0.15 Separation (nm) Separation (nm) -! 0.15 0 Separation (nm) Figure B-5 Fits of F/r versus separation for the system hematite-lnconel600 as a function of ammonia concentration for pH = 6 to 10. The concentration of added amine is indicated in units of mM. Units for F/r are mN/m. Energy required by a lym particle to surmount a force barrier of 0.04 mN/m is 49kT. B-6 0.3 0.3 \0,5mM pH10 PH 9 0,5mM 0.15 0.15 -- 0 0 --. I o 50 mM 2. -0.15 -0.15 Separation (nm) Separation (nm) 0.3 pH7 I / 0.15 0.15 0,5 mM 0 -0.15 Separation (nm) Separation (nm) 0.3 0.15 0 4t -0.15 Separation (nm) Figure B-6 Fits of F/r versus separation for the system hematite-/lnconel600 as a function of ethanolamine concentration for pH = 6 to 10. The concentration of added amine is indicated in units of mM. Units for F/r are mN/m. Energy required by a l-pm particle to surmount a force barrier of 0.04 mN/m is 49kT. B-7 0.2 0.2 pH10 1 PH9 0.15 0.15 _L 1 OmM 0.1 0.1 0.05 0.05 0 0 -0.05 -0.05 Separation (nm) Separation (nm) 0.2 0.15 PH8 0.1 0,5mM 0.05 0 0 0 10 20 30 1 -0.05 L -0.05 Separation (nm) Separation(nm) 0.1 0.05 0 -0.05 Separation (run) Figure B-7 Fits of F/r versus separation for the system hematite-lnconel600 as a function of dimethylamine concentration for pH = 6 to 10. The concentration of added amine is indicated in units of mhtl. Units for F/r are mN/m. Energy required by a l-pm particle to surmount a force barrier of 0.04 mN/m is 49kT. B-8 Table B-l Change in the surface charge density (mC/m*) on magnetite after the adsorption of amine. A positive change corresponds to a surface that is less negative. *A surface charge density of 1 mC/m corresponds to approximately 1 electronic charge per 200 nm . Table B-2: Change in the surface charge density (mC/m*) on hematite following the adsorption of amine. A positive change corresponds to a surface that is less negative. A surface charge density of 1 mC/m corresponds to approximately 1 electronic charge per 200 nm*. B-9 APPENDIX C Loop Deposition Test Results Table C-l : Loop chemistry and operating conditions for each test. Experimental Conditions Exp.lD P q” m” CTank C Loop [A] Tank [A] Loop pH Tank pH loop 02 Nd-h MPa kW/m2 kg/m% mg/kg mg/kg mmol/kg mmol/kg pH unit PH unit c19/kg b@kg EXPERIMENTS WITH MAGNETITE MORPHOLINE CHEMISTRY DO97 5.7 222 295 238 1.0 0.861 0.178 9.21 9.31 40 DlOl 5.7 223 298 66 0.76 2.169 0.249 9.21 9.18 45 D119 5.5 225 316 950 1.12 0.683 0.142 9.24 9.29 25 AMMONIA CHEMISTRY D120 5.7 239 318 682 2.90 0.143 0.071 9.74 9.58 2 DIMETHYLAMINE CHEMISTRY DlOO 5.7 225 287 70 0.52 0.004 0.027 9.17 9.12 75 D105 5.6 223 304 62 0.88 0.377 0.046 9.19 9.17 100 POTASSIUM HYDROXIDE CHEMISTRY DO98 5.6 223 294 122 0.78 0.068 0.036 9.02 8.85 53 D103 5.7 224 317 72 0.54 0.048 0.043 8.98 9.03 43 PYRROLIDINE CHEMISTRY DO99 5.6 227 299 134 1.48 0.035 0.024 9.19 9.04 75 D117 5.6 227 284 46 0.80 0.063 0.031 9.05 9.01 40 3-METHOXYPROPYLAMINE CHEMISTRY D102 5.6 221 304 88 1.06 0.355 0.077 9.73 9.63 60 D104 5.8 219 319 62 0.76 0.976 0.087 9.68 9.62 55 4-AMINOBUTANOL CHEMISTRY D116 5.6 225 271 16 0.36 0.157 0.054 9.39 9.52 60 D118 5.7 222 304 74 0.66 0.146 0.040 9.47 9.51 43 EXPERIMENTS WITH HEMATITE ETHANOLAMINE CHEMISTRY D108 5.6 228 296 58 0.36 0.188 0.075 9.55 9.47 0 0 Dill 5.7 232 298 38 0.68 1.146 0.095 9.57 9.46 169 0 DIMETHYLAMINE CHEMISTRY D106 5.7 211 299 66 1.38 0.195 0.095 9.30 9.22 0 55 D114 5.5 225 288 128 1.92 0.089 0.050 9.20 9.02 405 0 POTASSIUM HYDROXIDE CHEMISTRY D107 5.5 227 318 24 1.56 0.135 0.027 8.97 8.95 23 38 D109 5.6 229 292 104 9.60 0.143 0.037 6.92 8.94 125 0 D113 5.5 226 287 16 0.22 0.089 0.032 8.95 8.94 8 0 D115 5.6 231 278 150 1.82 0.205 0.022 8.99 9.01 213 0 3-METHOXYPROPYLAMINE CHEMISTRY DllO 5.7 230 300 40 0.54 0.510 0.012 9.65 9.61 265 0 D112 5.5 233 285 40 0.48 0.222 0.080 9.77 9.70 74 0 C-l Table C-2: Database of all the H3 loop deposition results for magnetite, Feo04. Remarks Exp.ID I c-2 Table C-3: Database of all the H3 loop deposition results for hematite, FezOo Kp for Forced Convection, kg/m% at single at X - 0.03 at X - 0.25 at X - 0.5 phase IORPHOLINF CHEMISTI I 02 DO46 2.74E-02 02 DO47 2.7OE-02 02 DO56 1.33E-02 02 DO57 5.14E-03 THANOLAMINE CHEMI TRY 02 DO60 2.10E-03 02 DO61 2.17E-02 no O2 DO79 2.34E-04 1.27E-02 6.91E-04 no 02 DO80 1 BE-03 2.69E-02 5.10E-04 no O2 D108 1.243-03 1.593-03 7.613-04 2.553-03 6.723-04 3.633-03 02 Dlll 8.603-03 1.2OE-03 9.813-04 3.483-04 4.383-04 4.403-04 MMONIA CHEMISTRY 02 DO48 8.84E-03 02 DO49 2.69E-03 02 DO58 4.28E-02 02 DO59 2.52E-02 )IMETHYLAMINE CHEIv STRY 02 DO77 3.46E-03 2.68E-02 3.3OE-03 02 DO78 5.32E-04 5.OOE-02 l.l6E-03 no O2 D106 7.813-04 6.083-04 7.443-04 3.563-04 3.433-04 4.873-04 02 D114 5.883-03 1.353-02 1.51E-04 1.873-04 9.11E-04 3.143-03 ‘OTASSIUM HYDROXID CHEMISTRY no O2 D107 3.093-04 5.093-04 2.773-04 1.573-04 2.153-04 7.223-04 02 D109 3.083-03 2.733-04 1.833-04 2.913-04 6.483-04 1.51E-04 02 D113 1.773-03 4.253-03 1.883-04 7.543-04 l.O7E-03 2.793-02 02 D115 4.26393 2.823-03 l.l7E-04 2.583-04 7.973-04 1.673-03 METHOXYPROPYLAM E CHEMISTRY 02 DllO 6.01E-04 1.573-04 1.643-04 2.173-04 1.483-04 8.743-05 D112 l.O7E-03 7.723-04 1.20E-04 1.453-04 9.643-05 9.323-05 02 - _ .__ ,egend: “02”-dissolved oxygen present in loop water, “no 02”-no oxygen present. The new results (of the current program) are in bold type. c-3 AECL Chalk River Laboratories, H3 Loop DO97--Fe304 + Morpholine S.OE-03 7.OE-03 7 6.OE-03 Q t4. 250 5.OE-03 E B & F 200 2.OE-03 l.OE-03 O.OE+OO -0.4 0 0.2 0.4 0.6 0.8 Mixture Quality [-] Figure C-l Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. XL Chalk River Laboratories, H3 Loop DlOl--Fe304 + Momholine I slE-03 - 300 c 4.16 I li : 7 tff:-01 t. c - 250 E o! 1 E :: E F L -2 .200 1 lR.-tU E 2 z.ofs-at I .Mo4 O.OE+OO 150 -0.4 0 0.1 0.2 0.3 0.4 0.5 0.6 0.1 Mixhm Quality [-I Figure C-2 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section. c-4 AECL chalk River Laboratories, H3 Loop D119--Fe304 + Morpholine 1.4Ero3 ,- 300 Axial Position on Ur H*d Secdons [ml c 2.;0 *.A 4.10 1.2EA3 + a j 1.0&03 s 4 8.OE-04 m 3 3 ‘f 6.OE-04 B z? jj 4.0&04 z” 2.0~04 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-] Figure C-3 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. AECL Chalk River Laboratories, H3 Loop D120--Fe304 + NH4OH 3.OE-03 - 300 0.10 1.50 2.10 2.70 4.10 x++ 2.5B03 A&+-+-e+ 7 g? FL 2.OE-03 Y 2 d A O.OE+OO 150 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-] Figure C-4 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations-on the unheated (adiabatic) test section. c-5 DlCG-Fe304 + DMA 300 150 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-] Figure C-5 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. AECL Chalk River Laboratories, H3 Loop D105--Fe304 + DMA 6.OE-04 O.OE+OO -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-] Figure C-6 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. El indicates locations on the unheated (adiabatic) test section. C-6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-I Figure C-7 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section. AECL Chalk River Laboratories, H3 Loop DlOSFe304 + KOH 5.OE-03 : - 300 Axial Position on Ur Iievcd Saions [ml + k -w-x, AYAW - t. 1 L - &I -- 250 E ().l)E+oo~ : : : : -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-] Figure C-8 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. c-7 AECL Chalk River Laboratories, H3 Loop DO99--Fe304 + Pyrrolidi 3.5B03 fi 300 Y.“...W ,. 150 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-I Figure C-9 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. AECL chalk River Laboratories. H3 IBOD D117--Fe304 + Pyrrolidine 3.5EO3 3.OEO3 7 “E B 2.5E-03 y” 3 2.OEO3 B ‘a ‘% 1.5E-03 B 0 a 5 l.OEO3 @ r” 5.OE-04 O.OE+OO -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-I Figure C-10 Normalized deposition rate as a function of steam quality. 0 indicates locatlons along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. C-8 AECL Chalk River Laboratories, H3 Loop D102--Fe304 + h&‘A 6.OE-04 300 I hill Porihn on tk Heak.d Sections [III, 4 c 0.10 1.50 5.0~04 a & $ a 4.OE-04 Y s I”‘i 2 .g 3.OE-04 .z g B 2x 2.OE-04 5 0 E s 1 .OE-04 hfcl O.OE+oo~ : : : : : : : : I 1150 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 Mixture Quality [-] Figure C-l 1 Normalized deposltion rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. AECL Chalk River Laboratories, H3 Loop D104--Fe304 + h4PA Axisl Porilion on the Heed Sectim [ml 300 250 E e B 3 8 F 200 = 4.OE-w 2.OE-04 O.OE+OO 150 -0.4 0 0.2 0.4 0.6 0.8 Mixture Quality [-] Figure C-12 Normalized deposltion rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section. c-9 AECL Chalk River Laboratories. H3 Loop Dl l&Fe304 + 4-AB 1.s03 -- 7 3 l.OE-03 -- Y, x” t 8.OE-04 -- rx x ‘P g 6.OEO4 -- B i 4.owM :- z 2.0~09 -- O.OE+oo! : : : : : I : c,so -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 Mixture Quality I-] Figure C-13 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section. AECL Chalk River Laboratories, H3 Loop D118--Fe304 + 4-AB 9.OE-04 -j ._:_l”.~...__ ._.L...... 8.OEXM t 7 7.oEM4 “E B sL 6.OEC4 - 250 Y 3 g 2 S.OE-04 I O.OE+OO m 150 -0.4 -0.2 0 0.4 0.6 0.8 hIixture!&lity [-] Figure C-14 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. c-10 AECL Chalk River Laboratories, H3 Loop D108--Fe203 + ETA 2.OE-03 - 300 0.2 0.4 0.6 0.8 Mixture Quality [-] Figure C-15 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. 6,0E02AEcL chalk River Labomnias, H3 Loop Dl 1 l--Fe203 + ETA 300 S.OEoZ 7 zl 2 4.OE02 250 2 (Y 5 3 +K*-nnsuUn e 8 3.OE-02 6 P g g 1 t- 1 2.oE-02 200 % l.OE-02 O.OE+OO 150 -0.4 -0.2 0 Mixht=GitY 1-l 0.4 0.6 0.8 Figure C-16 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. •i indicates locations on the unheated (adiabatic) test section c-11 AECL Chalk River Laboratories, H3 Loop DlO6--Fe203 + DMA 2.OE-03 0 300 Aria! Position on Ihe Healed Sectiom Iml O.OE+OO, : : : : I 7150 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-] Figure C-17 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section. AECL Chalk River Laboratories, H3 Loop D114--Fe203 + DMA 1.6&02 300 Adal Poritinnnnthe Heed Scctiom Iml 7 5 1.2E-02 25 - 250 2 -. s d 8.OEO3 z 2 6.OE-03 -. w ” B 8 4.OE-03 -- z in,, I.. : : 150 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-I Figure C-18 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. c-12 AECL Chalk River Laboratories, H3 Loop D107--Fe203 + KOH 2.OE-03 300 AXOI Por~trm on tie Hasted Sccbom [ml I 1 BE-03 -.-I 0.10 1.50 - 2.10 2.70 4.10 J+++ -7% 2.oE-04 -- E a o-4’ ‘% o.oE+ool...;...:...:...:.~,:... 150 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-I Figure C-19 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. Cl indicates locations on the unheated (adiabatic) test section. AEXX Chalk River Laboratories, I-I3 Loop D109--Fe203 + KOH 8.OE-03 - 300 ma! Posdion on Ule Heated Sections Iml .250 G L I E 200 g 2.0503 -- g 150 0.2 h4ixtwe Qwlity [-] Figure C-20 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. c-13 AECL Chalk River Labor@oties, H3 Loop Dll3--Fe203 + KOH 6.OEO2 r i 0.10 1.50 2.10 2.m 4.10 5.OE-02 F $ 2 4.OE02 : :a5 3.OJGO2 8 P 0 1 2’oE-02 B I .OE-02 O.OE+OO c -0.4 -0.2 0 0.2 0.4 0.6 0.8 h4ixhm Quality 1-l Figure C-21 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. AECL Chalk River Laboratories. H3 Loop D115--Fe203 + KOH 9 01:-03 J 300 -- 250 E r I; 6 % -- 200 i 0 A i._/0 LOE-03 -- E E R _j O.OE+OOq , .“” ; a a : : : , ; , , ~150 I -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-] I Figure C-22 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. c-14 AECL CWk River Laboratories, H3 Loop Dl IO-Fe203 + MPA 8.OEO3 300 7.oE-03 -- So c $, 6.OE-03 r. s 250 0 5.OEO3 2 E 8 e :; 4.OM3 S $ ;B 3.oE-03 8 g gz 200 2 2.OEo3 1.0~03 o.oE+OO 150 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-I L Figure C-23 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatic) test section. 0 indicates locations on the unheated (adiabatic) test section. AECL Chalk Rim Laboratories, H3 Loop D112-Fe203 + MPA 8.OE-03 300 0.10 1.M 2.10 2’10 4.10 7.OE-03 ! )7x-----o g 6.OE-03 f- 0 -- 250 je0 5.OE-03 -- z :g 4.OE-03 -- cf * 3.OE-03 -- l.OE-03 -- -0.4 -0.2 0 0.2 0.4 0.6 0.8 Mixture Quality [-] Figure C-24 Normalized deposition rate as a function of steam quality. 0 indicates locations along the heated (diabatlc) test section. Cl indicates locations on the unheated (adiabatic) test section. c-15 MAGNETIC FIELD INSIDE I-600 TEST SECTION The magnetic flux density was measured inside a I-600 test section on the B250 H3 loop using a Gauss/Tesla meter with two types of Hall-effect probes: axial and transverse. The magnetic field is of interest because it could affect the movement of ferromagnetic magnetite particles approaching the tube wall during the deposition experiments and thus possibly alter the results. The test section is electrically heated using alternating current. The electrical current is 600 A during a typical deposition experiment. From Ampere’s Law and the symmetry of the test section, there should be no magnetic field inside the test section in the ideal case. The test set up was prepared as follows: the probe was inserted into a 5/16” ( 7.94 mm) OD Teflon tube plugged at one end with a cork stopper. This Teflon tubing was then inserted into the I-600 test section and a 1/2” (12.7 mm) tee was installed to allow a 1 L flow throughout the test section. The heated test section was 1.6 m. The probe tip was located 25 cm from the test section inlet. The conditions during the measurements were as follows: flow rate = 1 L/mm, pressure < 0.25 MPa, inlet temperature = 22°C - 63°C and outlet temperature up to 100°C. The current was varied from 0 to 300 A. Three series of measurements were made using: (1) axial probe, (2) transverse probe and (3) transverse probe rotated 90 degrees with respect to Series 2. The results of these measurements are shown in Figure C-25. The values of the magnetic field intensity extrapolated to the conditions expected during the deposition experiments are: 0.14 mT - in the tube axial direction, 2.05 mT - in the tube transverse direction, 1.56 mT - in the tube transverse direction, perpendicular to the previous direction. From gravitational settling tests performed on a magnetite suspension as a function of external magnetic field strength, it was deduced that for a magnetic field strength of 2 mT the force on a magnetite particle is < 0.01% of the force of gravity. Thus, it is concluded that the magnetic field that develops inside the tube as a result of resistive heating with alternating current does not have a significant effect on the measured particle deposition rates in this investigation. C-16 Magnetic field inside I-600 test section 2.5 2 F S Q 1.5 B A Axial direction rW2 l Traasvzrse direction .> 1 0 Transverse rotated 90” -Linear (Transverse direction) B -Linear (Axial direction) 3 -Linear (Transverse rotated 90”) 0.5 0 0 loo 200 300 400 500 600 700 800 Current (A) Figure C-25 Magnetic flux density from axial and transverse direction c-17 APPENDIX D DEFINITION OF THERMOHYDRAULIC PARAMETERS UNDER TWO-PHASE FLOW AND DEVELOPMENT OF DROPLET IMPINGEMENT FOULING MODEL STEAM QUALITY The mass quality is defined as the mass fraction of the vapour phase in the total mass flow of the 2-phase mixture: x=-.mG (D-1) 9P The thermodynamic quality is defined as x= HTP - HL SAT (D-2) H'.L-G The mass quality and the thermodynamic quality are equal if the system is under thermodynamic equilibrium. Real diabatic systems cannot be in thermodynamic equilibrium, and the mass quality and thermodynamic quality are, in general, different. Hsu and Graham (1986) give an example of non-equilibrium quality distribution. Their sketch is reproduced in Figure D-l. It demon~tmk~ that the true quality exceeds the equilibrium quality at subcooled boiling and at flow-hoilmf with low steam quality. The opposite is true for high steam qualities. satuntbn pokrt Ji ?a ’ P d 0 0 1.0 Figure D-l Schematics of the steam quality change for non-equiilbrium P-phase flow. Re- printed from Tong and Tang (1997). D-l All calculations presented in this report were performed under the assumption that the mass quality equals the thermodynamic quality. SUPERFICIAL MASS FLUX, VELOCITY, AND REYNOLDS NUMBER The superficial mass flux of liquid, rn’r_, is calculated as if only liquid flowed in the channel. The liquid superficial velocity is obtained by dividing the superficial mass flux by liquid density. The liquid-only Reynolds number is defined as m’L D =- ReL (D-3) PL This value is identical to the Reynolds number of the liquid film UfPL46 Re Lf = , (D-4) PL which justifies the usage of the Reynolds number based on the liquid superficial mass flux. Analogous quantities can be obtained for the gas phase. The justification for their usage is that the gas phase typically occupies most of the channel cross-sectional area; therefore, the superficial values are close to the real values for gas. FLOW PATTERNS The Hewitt and Roberts flow pattern map (Whalley, 1987) can be used for approximate evaluation of the flow patterns for vertical upwards flow of water-steam mixture over a range of pressures in small diameter tubes (10 to 30 mm). Figure D-2 shows a flow map from Whalley (1987). It is overlapped with a graph obtained for water-steam mixture at 5.6 MPa at different steam qualities and mass fluxes. For the experimental conditions of m” = 300 kg/m*s, the graph predicts that slug flow occurs below 5% quality, followed by the churn flow regime (up to X = 18%), followed by annular flow. The values on the axes may be interpreted as the liquid- and gas-phase momentum fluxes. D-2 Mass Flux [kg/m%]: - 50 -100 t200 4300 -+500 --c loo0 ‘Wispy* annular 4 1EO 1El lE2 lE3 lE4 lE5 lE6 m’L% Ikg/s2ml Figure D-2 Hewitt and Roberts flow pattern map (Whalley, 1987) for vertical upwards flow inside a tube. An analytical criterion for the transition from chum to annular flow is that of Taitel and Dukler (L. K.H. Leung and D.C. Groeneveld, Chalk River Laboratories, personal communication, 1998). According to this criterion, annular flow occurs if --&(C%PG2(P~-PG))t <' . (D-5) This criterion predicts that, under the experimental conditions, the transition to annular flow regime would occur at X = 0.20. Another simple, analytical criterion for the transition from chum to annular flow is given by Wadekar and Kenning (1997): jc* c 1 for slug/chum flow, and jc* > 1 for annular flow, where, . * m'X J G = (D-6) ( gD(PL - PC )PcG)~‘~ . According to this criterion, under the experimental conditions the transition from chum to annular flow would occur at quality X = 0.16. Annular flow is defined as “a flow regime of 2-phase gas-liquid flow characterized by the presence of a liquid film flowing on the channel wall and with the gas flowing in the gas core” (Hewitt et al., 1997). The numbers given above should be treated as approximate only since the flow maps are not exact. Thus the boundaries for the transitions between the flow patterns are not sharp. D-3 It should also be borne in mind that these flow maps were created mostly for adiabatic conditions. There are several reasons for the presence of heat transfer to affect the transitions. At the experimental conditions with heat flux, the true quality is expected to exceed the thermodynamic quality for low qualities, and lag behind the thermodynamic quality at high qualities. Another important aspect of annular flow is its developing nature. Up to 400 tube diameters may be required to achieve “equilibrium” (Whalley, 1987). Examples of phenomena that require significant length for developing are the entrained fraction of the liquid, which increases steadily along the tube, and the film thickness, which decreases. A true equilibrium may never be achieved, even under adiabatic conditions because of the pressure drop and flushing off the liquid. Under diabatic conditions, annular flow is by definition developing because of constant increase in steam quality. Therefore, diabatic and adiabatic flow patterns are generally different, and adiabatic flow maps are used for diabatic conditions for lack of better data. Hosler (cited in Tong and Tang, 1997) conducted measurements of flow pattern transition for flow boiling under diabatic conditions in rectangular channels. According to his data, the transition to annular flow would occur at X = 0.20 at the conditions of our experimental program. Plug, chum, and annular flow patterns have their equivalents in 2-phase flow in rod bundles. The transitions between the patterns occur, however, at different conditions. According to Vankateswarara (cited in Tong and Tang, 1997), the transition to annular flow in rod bundles takes place at a gas phase superficial velocity of 7 to 11 m/s for the liquid flow rates of interest. This velocity s equivalent to 0.65 < X < 1 .O under our experimental conditions. The quality at which the transition takes place will decrease linearly with increasing mass flux. The flow patterns are important for system characterization because the geometry of the flow is different for different flow patterns. The heat-transfer characteristics of annular flow are very different from those of slug-chum flow. There is almost no difference between the slug and the chum flow regions; from the point of view of heat transfer, chum flow may be treated as a special case of slug flow (Wadekar and Kenning, 1997). VOID FRACTION Void fraction is defined as the volume fraction of the gas phase in the gas-liquid mixture over a length of the flow channel: VG a= (D-7) vL+vG . It can be presented in terms of quality and the slip ratio (Hewitt et al., 1994): A a= (D-8) X+S(l-X)2 . For low values of the reduced pressure (ratio of the pressure to the critical pressure, approximately 4 under the experimental conditions), the empirical correlation of Armand is recommended for prediction of void fraction in the annular flow regime (Hewitt et al., 1997): D-4 4+;b a=l- (D-9) 5+b where, m;; (D-10) P= m9GpGm; 9 -+- PC PL , (D-l 1) a = 0.69 + (1 - p)(4 + 2 1.9,/Fr, ) . (D-12) The constants a, b and p are introduced for convenience of notation only, and do not have special definitions. The liquid-only Froude number is , 2 FrL ~5 (D-13) PL2@ . Another way to estimate the void fraction is to use Equation (D-8) with the slip ratio calculated according to an existing empirical correlation, e.g., Premoli correlation, which is discussed later. Estimation of the void fraction can also be made by using the homogeneous model (Equation (D-8) with S = 1). This tends to overestimate the true void fraction. Under the experimental conditions, the void fraction is expected to reach over 90% for X - 0.5. SLIP RATIO The slip ratio is the ratio of the velocity of the gas phase to the velocity of the liquid phase: s=UG . (D- 14) UL The void fraction and slip ratio are closely related. The slip ratio can be calculated from the void fraction (e.g., the Armand correlation) and from Equation (D-8). The Premoli correlation (also known as the CISE correlation) can be used to calculate the slip ratio directly: Y (D- 15) l+yE, D-5 P (D-16) Y=l_p ’ p= xpL (D- 17) xp, +(I- xl& ’ 0.22 E1 = 1.578 Re-‘.19 , (D-18) -0.08 E2 = 0.0273We Re-o.51 , and, (D-19) 92 D w(ym,. (D-20) OPL The constants El, E2, y, and p are introduced for convenience of notation and do not have special definitions. Another particularly simple method of calculating the slip ratio is the Chisholm correlation (Whalley, 1987): s+-x[&)f . (D-21) An even simpler, but less accurate, correlation is the Zivi correlation (Whalley, 1987): 1 (D-22) The accur+ of the various correlations has been observed to decrease in the following order: PremolI > Ctu&&n. > Zivi (Whalley, 1987). The standard deviation of the mean density calculated on the h;L\ib of the Premoli correlation is approximately 40%. TWO-PHASE DENSll3 The 2-phase density is defined as (Hewitt et al.,1994) pTp = (I- a)pL + apG ’ (D-23) which, for homogenous flow, is equivalent to (D-24) D-6 VELOCITY OF THE PHASES When the thermodynamic quality and the void fraction (or the slip ratio) are known, the velocity of the liquid and gas phases are simply The gas velocity calculated using this equation is a very good approximation of the value in real systems. For liquid, however, the radial velocity exhibits a considerable profile as the tube wall is approached and, therefore, the calculated value represents only a mean. SINGLE-PHASE SHEAR STRESS, FRICTION VELOCITY, FRICTION FACTOR, AND PRESSURE DROP The Fanning equation represents the force balance for flow inside a channel: AjlJP& = ?jZvoN . (D-26) The shear stress is z = fFamin*Pu2 (D-27) 2 ’ The frictional velocity is defined as z u*= -. (D-28) dP From Equations (D-27) and (D-28), the frictional velocity is Fanning u*= -uf d 2 (D-29) Two different friction factors are found in the literature: the Moody friction factor and Fanning friction factor. The relationship between them is (D-30) f Moody = 4fFanning . For laminar flow, the Hagen-Poiseuille equation is used for prediction of the single-phase friction factor: (D-3 1) f Fanning = $ . For turbulent flow in smooth pipes, the Blasius equation may be used: fEatming = ~~ 3000 D-7 The implicit Colebrook-White formula (Hewitt et al., 1997) is recommended for prediction of the Moody friction factor for transitional and fully developed single-phase turbulent flow (gas or liquid) in fully rough or smooth tubes: 1 E/D 2.5 1 = -0.861og - (D-33) f M*ol@“~5 3.7 + fMood?.o.5 Re The single-phase frictional pressure drop is predicted from the D’Arcy-Weisbach equation: @SP, fric = i fhloody ’2 PLU2 . (D-34) TWO-PHASE PRESSURE DROP The 2-phase pressure drop consists of 3 parts: the acceleration pressure drop, the gravitational pressure drop, and the frictional pressure drop: *TP = DTP,acc + hpTP,grav + uTP,fric . (D-35) The 2-phase acceleration pressure drop is calculated from the momentum balance (Collier and Thome, 1994): APTP,occ (D-36) The 2-phase gravitational pressure drop is calculated from (Collier and Theme, 1994): APTP, grav = g sin( 8)( a& + (l- a)&)& , (D-37) where a is the mean void fraction over the tube length Az: 1 z+A.? I a(z)& . a=z z DTP,fric = fric . (D-39) When 2 1000 (it is approximately 5.5 for the experimental condition), the recommended correlation for evaluation of the single-phase multiplier is that of Friedel (Collier and Thome, 1994): D-8 #f. = A, + 3’24A2 A3 (D-40) Fr0.045We0.035 ' where: (D-41) (D-42) (D-43) FrTp = ma 0-W &p2gD ’ m’2 D We, = - , (D-45) pTPO and pip is the homogenous mixture density defined by Equation (D-24). The constants Ai, A2 and A3 are introduced for convenience of notation only and do not have special definitions. The standard deviation of the Friedler correlation is 40% to 50%, an accuracy considered very good for 2-phase flow conditions. INCEPTION OF DROPLET ENTRAINMENT As the velocity of a gas increases, the initially stable wall film becomes wavy (incipience of ripples), then the waves become irregular (onset of 2-dimensional ripples), and, with further increased velocity, large-amplitude concentration (density) waves appear (inception of roll waves); finally, the tops of some of the waves can break and liquid droplets becomes suspended in the gas core (onset of entrainment). For entrainment to occur, both liquid and gas flow rates must exceed critical values. The critical liquid film Reynolds number is predicted by (Collier and Thome, 1994): Re,,, = exp[5.8504 + 0.4249[ z][ %,“I . (D-46) When the above condition is met, the onset of entrainment occurs if the gas volumetric flux is larger than (D-47) where the constant A is given different values by different authors: either 1.5 x 104 or 2.42 x 10e4 (Collier and Thome, 1994). D-9 For 200 c ReL< 3000, the amount of entrainment is a function of both the vapour and liquid flow rates, and for ReL > 3000, the entrainment depends mainly on the velocity of the vapour (Collier and Thome, 1994). Another practical entrainment-inception model is presented by Hewitt (1982). The inception of entrainment occurs when the gas volumetric flux is greater than for N, c-l-, Re, > 1635 for N, >h, Re, > 1635 j, =< (D-48) for N, < A, Re, c 1635 for N, > 6, Re, < 1635 where the viscosity number, N,, is defined as N, = (D-49) 112 . DROPLET ENTRAINMENT RATE The droplets appear in the gas core when the inter-facial shear stress is capable of overcoming the forces of cohesion of the liquid. The droplet entrainment rate can be evaluated from (Collier and Thome, 1994) J, = 5.75. 1oe5m’G[ ( m’L,f -m’L,ctit@)~6 9 (D-50) where m’L,cct is the liquid mass flux corresponding to the critical Reynolds number of the liquid defined by Equation (D-46). Under diabatic conditions, the boiling process can additionally enhance entrainment. DROPLET DEPOSITION RATE The droplets entrained in the gas core may be re-deposited onto the liquid film at the tube wall. The droplet deposition rate can be presented as (Hewitt and Govan, 1990a, b) J, =K,C , (D-5 1) where C, the mean homogenous droplet concentration in the vapour core, is given by D-10 mL,E C= 9 (D-52) mL,E mG -+- pL pG The Govan correlation (Collier and Thome, 1994) can be used for predicting the droplet deposition coefficient 1 f c< 0.3 pG Kdep = (D-53) f 5 > 0.3 Or pG ENTRAINED FRACTION The fraction of entrained liquid is defined as a ratio of the flow rate of the liquid as droplets to the total liquid flow rate: drop mL,tOtOl thewhen developsAnnular flow reached in pctical systems because of the pressure drop. Under diabatic condition, the system is add~tmmllp removed from steady state because the quality increases along the tube and therefore the flow conditions constantly change. Attempts, however, were made to establish the stcrrd! -\t;rtc vrrluc of the entrained fraction. The sunplc. but not highly recommended, Ishii-Mishima correlations are presented by Whalley, (1987,. E = tanh( 7.25. 10m7 ui2.5d’1’25 ReLo.25) , (D-55) whcrc (D-56) d=d(g(pL;pG)j _ (D-57) D-11 Because the deposition rate, the entrainment rate, and the entrained fraction are interrelated, the equations describing these phenomena must be solved simultaneously. TURBULENCE INTENSITY IN THE GAS CORE To describe the turbulence, the fluid velocity may be represented as a sum of 2 components, the mean velocity and a fluctuation from the mean (White, 1994): - u=u+u’ . (D-58) The turbulence intensity is defined as a time-average mean square of the fluctuation: lT 7 =- u”dt I TO The distribution of the axial velocity of the gas phase was found experimentally to be approximately normal, as expected for a truly random phenomenon (Azzopardi and Teixeira, 1994a). The normality of the circumferential and radial velocity distribution was not tested, but there is no reason to believe that they are not normal. In the same investigation, the radial and circumferential turbulence intensity were found to be approximately equal. The axial turbulence intensity, which is of no interest in this investigation, was found to be higher. The radial turbulence intensity was in the range of 8% to 15% of the axial gas velocity. For pure gas flow (only gas in the core, no entrainment), the turbulence intensity was shown to exhibit a characteristic profile in the radial direction when made nondimensional with the friction velocity (Azzopardi and Teixeira, 1994a), with extrapolated ratios of approximately 0.8 at the tube axis and 2 at the gas-core periphery. Therefore, utilizing Equations (D-26) and (D-28), the gas-core turbulence intensity at the core periphery can be approximated by D”G.ftic * (D-60) P The presence of the entrained droplets additionally enhanced turbulence. The variance of the radial velocity distribution of the liquid droplets entrained in the gas core is postulated to be proportional to the gas-core turbulence intensity: - U’drop,x,RMS = 2cf u; = cf flbPG,fric . (D-61) P Turbulence is scale-dependent, and only turbulence at the particle-size scale and above is relevant. It is recommended that a better relationship be developed for the velocity distribution of particles in turbulent flow, or the value of the correlation factor, G be determined. D-12 DROPLET SIZE, VELOCITY AND DISTRIBUTION Azzopardi and Teixeira (1994b) investigated drop sizes and velocities in vertical annular flow of an air-water mixture at relatively low mass fluxes of 16 to 48 kg/m2s for the liquid and 25 to 56 kg/m*s for the gas phase using the phase Doppler anemometry technique. The mean droplets velocity was approximately equal to the gas superficial velocity, or 20% lower than the corresponding local velocities of the gas. Its standard deviation was 9% to 15 %, depending on the mean velocity (the higher the velocity, the lower the standard deviation). The velocity of the drops was relatively size-insensitive down to 100 pm, after which there was a tendency for the smallest investigated droplets (30 pm) to travel up to 25% faster than the largest ones (500 pm), the velocity of the former approaching the velocity of the gas. The radial profile of the drop axial velocity was relatively flat, with the droplets in the centre travelling 10% to 20% faster. The mean drop size also showed a radial distribution with the droplets closer to the interface having a 12% smaller Sauter diameter: c d,? yj p.32 =i. (D-62) c d,? The maximum droplet size is (Hewitt and Hall-Taylor, 1970): We,0 d,= , (D-63) PGUG-p where the critical Weber number, We,, is approximately 22. The parameter, t.+,, is the relative gas-particle velocity. FILM THICKNESS From the definition of the void fraction and neglecting the volume of the entrained droplets, the film thickness can be calculated from s=t(l--&)=$(1-a) . (D-64) It has to be emphasized that the film thickness is typically non-uniform because of disturbance waves of amplitude that are 5- to 6-fold larger than the film thickness (Hewitt et al., 1997), and Equation (D-64) computes the mean value. If the entrainment rate is significant the calculation of the film thickness is less straightforward. One method is to calculate the 2-phase pressure drop and, through the inter-facial shear stress, utilize the correlation for the interfacial friction factor to calculate the film thickness. D-13 The interfacial friction factor is calculated by (D-65) The calculations are conducted for the gas phase because the velocity of the gas is easier to estimate than the velocity of the liquid. According to Whalley (1987), the inter-facial friction factor may be given by either fFanning,i = fFanning,G ’ (D-66) or (D-67) where fFauoiug,G is is calculated using Equation (D-32). These correlations, although probably not very accurate, permit estimation of the liquid film thickness. A more complicated method is to employ the triangular relationship. The triangular relationship is a set of dependencies bounding 3 variables: liquid film flow rate (kg/s), film shear stress, and the average film thickness. The triangular relationship permits the calculation of any one of these variables to be calculated if the values of the two remaining variables are known. D-14 NOMENCLATURE D = pipe diameter (m) C = concentration (kg mm3) H = enthalpy (kJ kg-‘) J = flux (kg me2 s-l) K = rate constant (kg mm2 s-i) P = pressure (Pa) Re = Reynolds number S = slip ratio V = volume (m3) X = mass or thermodynamic quality d = droplet diameter (m) g = gravitational acceleration (m sM2) j = volumetric flux (m s-‘) m = mass flow (kg s-l) m’ = mass flux (kg ni2 s-l) t = time (s) u = velocity (m s-‘) u* = friction velocity (m s-l) 2 = length (m) a = void fraction 6 = film thickness (m) p = dynamic viscosity (kg m’ s-‘) p = density (kg mm3) d = surface tension (N me’) ‘5 = shear stress (N me2) Subscripts d = deposition E = entrainment f=film G = gas or vapour G-p = relative gas-particle L = liquid L-G = vaporization SAT = saturation “IF = two-phase D-15 REFERENCES Azzopardi, B.J. and J.C.F. Teixeira (1994a), “Detailed Measurements of Vertical Annular Two- Phase Flow-Part II: Gas Core Turbulence”, J. Fluids Eng. 116,796-800. Azzopardi, B.J. and J.C.F. Teixeira (1999b). “Detailed Measurements of Vertical Annular Two- Phase Flow-Part I: Drop Velocities and Sizes”, J. Fluids Eng. 116,792-792. Collier J.G. and J.R. Thome (1994). Convective Boiling and Condensation, Third Edition, Carendon Press, Oxford. Hewitt G.F. and N.S. Hall-Taylor (1970). Annular Two-Phase Flow, Pergamon Press, Oxford. Hewitt G. F. ( 1982). “Flow Regimes” in-Handbook of Multiphase Systems G. Hetsroni ed., Hemisphere Publishing Corporation / McGraw-Hill Book Company, Washington, New York. Hewitt G.F. and A.H. Govan (1990a). “Phenomenological Modelling of Non-equilibrium Flow with Phase change”, Int. J. Heat Mass Transfer 33,229-242. Hewitt G. F. and A.H. Govan (199Ob). “Phenomena and Prediction in Annular Two-phase Flow. Invited Lecture”, Advances in Gas-Liquid Flows-1990. Presented at the winter annual meeting of the American Society of Mechanical Engineers, Dallas, Texas, November 25-30, International Symposium on Gas-Liquid Two-Phase Flows (1990: Dallas, Texas). Hewitt G.F. G.L. Shires, and T.R. Bott (1994). Process Heat Transfer, CRC Press, Boca Raton, New- Y’ork. Hewnt G. F.. G-L. Shires, and Y.V. Polezhaev (1997). International Encyclopedia of Heat and MIS.\ Iransfcr. CRC Press, Boca Raton, New York. Hsu. I’ j’.. R W. Grham (1986). Transport Processes in Boiling and Two-Phase Systems, American Nuclcw Society, Inc. La Grange Park, Illinois. Tong L.S. ;md Y.S. Tang (1997). Boiling Heat Transfer and Two-Phase Flow, Taylor and Francis. Bn~tol. Wadekar, V.V. and D.B.R. Kenning (1990), “Flow Boiling Heat Transfer in Vertical Slug and Churn Flow Region”. Presented at International Heat Transfer Conference, Jerusalem, Israel, 1990 August 19-24, Hemisphere Publishing, New York. Whalley P.B. (1987). Boiling, Condensation, and Gas-Liquid Flow, Clarendon Press, Oxford University Press. White F.M. (1994). Fluid Mechanics, McGraw-Hill Inc., New York, NY. D-16 APPENDIX E SEM MICROGRAPHS OF TUBE DEPOSITS E-l ((1) Figure E-l Morphology of surface deposits created under magnetite/morpholine chemistry, Experiment D097. (a) Tube G. flow boilin_g at X = -0.05 (15°C of subcooling). Relatively few single particles and some clusters present; (h) Tube K, flow boiling at X = 0.10. Numerous single particles possible with some recrystalization; (c) Tube 0, flow boiling at X = 0.25. Some particles and clusters present, possible with recrystalization. Some needle-shaped crystals; (d) Tube U. flow boiling at X = 0.50. Surface completely covered with needlc-shaped crystals. individual particles visible on the top of the crystals. This is the region in which the deposition rate increases rapidly. This deposition morphology is observed only occasionally--the frequency of its observation may indicate that a coincidence of factors is ncccssary for it to occur. or it may be a reflection of the transitory nature of the crystals. The identity of the phase was not established. gocthite is suspected. (e) Tube AD. two-phase forced convection (unheated test section) at X = 0.03. The particles deposited as dispersed single particles. This is a typical morphology for deposits formed under non-boiling conditions (either single- or two-phase conditions at low X). E-2 (4 (b) (d) (e) Figure E-2. Morphology of surface deposits created under magnetite/morpholine chemistry, run D119. This experiment aimed to achieve high surface coverage. In reality, only moderate surface coverage was obtained, but the deposit consolidation was among the highest ever observed. (b). and (c) Tube B, forced convectionkubcooled flow-boiling at X = -0.2 (-70°C subcooling). Well consolidated aggregates of particles, approximately 10 pm in size. (d) and (e), tube G, flow boiling at X = -0.05 (- 15°C of subcooling). Significant deposit clusteringke-crystalization leads to crystals exceeding 10 pm in size. In contrast with the previous sample, the aggregates are not distributed uniformly over the surface. E-3 (4 (b) Figure E-3. Morphology of surface deposits created under magnetite/ammonia chemistry, run D120. This experiment aimed to achieve high surface coverage. Only moderate coverage was obtained, but the deposit consolidation was among the highest ever observed. (a) Tube B, forced convection/flow boiling at X = -0.2 (-70°C subcooling). (b) Tube G, flow boiling X = -0.05 (- 15°C subcooling). In both cases, significant deposit clustering and re-crystalization leads to structures exceeding 10 pm in size. E-4 (a) (b) (d) (Cl (f-1 Figure E-4. Morphology of surface deposits created under magnetite/dimethylamine chemistry (Dl 00 and D105). (a) and (b) Tube B, flow boiling at X = -0.2 (-70°C subcooling). Clusters of particles. (c) Tube G, flow boiling X = -0.05 (-15C subcooling). Undeveloped structures and some particles in the region of approximately zero steam quality (nucleate boiling). (d) Tube K, flow boiling X = 0.1. Undeveloped structures. (e) Tube 0, flow boiling at X= 0.3, just upstream of the region of rapidly increasing deposition rate. Undeveloped structures. (f) Tube U, X = 0.5, the region of rapidly increasing deposition rate. Single particles and small clusters. E-S (4 (b) Figure E-5 Morphology of deposits created under magnetite/potassium hydroxide chemistry. (a) D098, Tube G, X = -0.05 (- 15°C subcooling). “Undeveloped” structures characteristic for the nucleate boiling region, which appear to reduces the sharpness of the surface details. (b) D103, Tube AH, two-phase force convection (no heat transfer) at X in the area of the very rapid increase of the deposition rate). E-6 (cl (4 (e) Figure E-6 Morphology of surface deposits created under magnetite/pyrrolidine chemistry control. (a) D099, Tube B, forced convection / subcooled flow boiling, X = -0.2 (-70°C subcooling). Clustered particles. (b) D099, tube G, X = -0.05 (- 15°C subcooling). Undeveloped structures. (c) D117, Tube B, flow-boiling X = -0.2 (-70°C subcooling). Needles of crystals approximately 1 pm long. (d) D117, tube G, X = -0.05 (-lS°C subcooling). Needles of crystals 0.3 pm long and less. (e) D117, Tube K, X = 0.10 (as well as further downstream). Isolated particles. E-7 (4 (b) (cl (4 Figure E-7 Morphology of surface deposits created under magnetite/3- methoxypropylamine chemistry (experiment D102). (a) and (b) Tube B, forced convectionkubcooled flow boiling, X = -0.2 (-70°C subcooling). Particle clustering. (c) Tube G, flow boiling, X = -0.05 (- 15°C subcooling). Undeveloped structures. (d) Tube K, X = 0.10. Individual particles (little clustering). E-8 (4 (b) (c) (4 Figure E-8 Morphology of surface deposits created under magnetite/4-aminobutanol chemistry. (a) D116, Tube B, forced convectionkubcooled flow boiling, X = -0.20 (70°C of subcooling). Particle clustering. (b) D118, Tube G, flow boiling, X = -0.05 (15°C of subcooling). Undeveloped structures often associated with nucleate boiling region. (c) D116, Tube K flow boiling, X = 0.10. Small crystals/isolated particles. (d) D116, Tube AH two-phase force convection mass transfer (unheated area) X = 0.50, (region of the rapid deposition rate increase). The particles are preferentially captured on the asperity protruding into the flow, particularly on its outermost surface. This is a direct illustration that the transport and attachment are governing the observed deposition, not re-entrainment (in which case, the cavities would be expected to fill up first). E-9 (4 (b) (cl (4 Figure E-9 Morphology of surface deposits created under hematite/ethanolamine chemistry, D108 and Dl 11. (a) Tube B forced convectionkubcooled flow boiling, X = -0.20 (-70°C of subcooling). Large particle clusters, up to 10 pm. (b) and (c) Tube G, nucleate flow boling, X = -0.05 (-15’C of subcooling). “Amorphous” features typically associated with nucleate boiling region. (d) Dl 11, Tube 0, flow boiling, X = 0.30. Single particles/crystals. E-IO (a) (b) Figure E-l 0 Morphology of surface deposits created under hematite/dimethylamine chemistry, hydrazine present, no oxygen, experiment D106. Magnetite particles can be detected only on some micrographs. (a) Tube B, forced convectionkubcooled flow boiling, X=-O.2 (70°C subcooling), small clusters. (b) Tube K, flow boiling, X = 0.1, single particles. E-11 (4 (b) (c> (4 Figure E-l 1 Morphology of surface deposits created under hematite/potassium hydroxide chemistry D113 and D115. (a) and (b) Tube B, forced convectionkubcooled flow boiling, X = -0.2 (70°C subcooling). Typical clusters, approximately 10 pm in size. (c) D115, Tube G subcooled flow boiling, X = - 0.05 (15°C subcooling). (d) D113, Tube U, subcooled flow boiling, X = 0.5. No particles detactable. E-12 (a) (b) (4 Figure E-l 2 Morphology of surface deposits created under hematite/3-methoxypropylamine chemistry, experiment Dll 0. (a) and (b) Tube B, forced convection/subcooled flow boiling, X = -0.2 (70°C subcooling). Typical clusters. (c) and (d) Tube G subcooled flow boiling, X = -0.05 (15°C subcooling). Undeveloped “amorphous” features in the region of nucleate boiling, with - 1 pm needle-like crystals appearing. (e) Tube U, flow boiling, X = 0.50. In the higher steam quality region, the surface features are sharp again, no amorphous material. E-13 (a) (b) (4 Figure E-l 3 Morphology of surface deposits created under hematite/3-methoxypropylamine chemistry, experiment D112. (a) and (b) Tube B, subcooled flow boiling, X = -0.2 (70°C subcooling). Heavy deposit, clustering typical for these conditions. (c) Tube G, subcooled flow boiling X = -0.05 (15°C subcooling). “Amorphous” material on the surface. (d). Tube 0, flow boiling X = 0.3. Needle- shaped crystals. E-14 AECL-12036 ISSN 0067-0367 To identify individual documents in the series, we have assigned an AECL-number to each. Please refer to the AECL-number when requesting additional copies of this document from: Information Centre, Information Management Branch AECL Chalk River, Ontario Canada KOJ 1 JO Fax: (613) 584-8144 Tel.: (613) 584-33 11 ext. 4623 Pour identifier les rapports individuels faisant par-tie de cette series, nous avons affect& un numero AECL-8 chacun d’eux. Veuillex indiquer le numCro AECL-lorsque vous demandez d’autres exemplaires de ce rapport au: Service de Distribuition des Documents Officiels EACL Chalk River (Ontario) Canada KOJ 1 JO Fax: (613) 584-8144 Tel.: (613) 584-3311 poste 4623 Copyright 0 Atomic Energy of Canada Limited, 2000