DOCSLIB.ORG

Critical Heat Flux and Subcooled Nucleate Boiling in Transient Region Between a Two-Dimensional Water Jet and a Heated Surface

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Critical Heat Flux and Subcooled Nucleate Boiling in Transient Region Between a Two-Dimensional Water Jet and a Heated Surface CRITICAL HEAT FLUX AND SUBCOOLED NUCLEATE BOILING IN TRANSIENT REGION BETWEEN A TWO-DIMENSIONAL WATER JET AND A HEATED SURFACE Yoshiki MIYASAKA, Shigeaki INADA AND YOSHIHIKO OWASE Department of Mechanical Engineering, GunmaUniversity, Kiryu 376 The present paper is concerned with a high subcooling water jet boiling system at the stagnation point. The purpose of the investigation is to obtain a high heat flux and to reveal the high heat flux mechanism. Most of the discussion in this paper is based on experimental results and con- cerns the effect of subcooling, jet velocity, and stagnation pressure on critical heat flux and nucleate boiling in the transient region. The entire range of the boiling curve is divided into three heat transfer regions which maybe hypothesized to exist in nucleate boiling. curves in subcooled pool boiling is discussed. Introduction In the previous study6\ the effect of forced con- Whenthe boiling phenomenonis used effectively in vection heat transfer on nucleate boiling was con- a technological application, it is convenient and im- sidered from the standpoint of superposition of the portant to removeenormousquantities of heat per heat flux. unit time and area from a heated surface and to ac- The present study was made within the same sub- complish this heat transfer at a relatively low surface cooling and the jet velocity ranges as in the previous temperature without burn-out of the boiling surface. paper. The important parameters of this study are Recently, a study of the effect of jet velocity on critical subcooling, the jet velocity, the stagnation pressure heat flux has been made by Monde and Katto7). and contamination of the boiling surface. Generally, Their experimentwascarried out with a systemcovered when the boiling surface is contaminated in some with a flowing film of saturated water at atmospheric degree, the coefficient of heat transfer increases pressure being maintained by a small circular jet of remarkably in the transient boiling region. In this water held at the center of the heated surface. study, it is considered that the boiling surface is not The present paper is concerned with a high sub- completely contaminated, but is moderately contami- cooling water jet boiling system at the stagnation nated. point. The purpose of the present investigation is Most of the discussion in this paper is based on the to obtain a high heat flux and to reveal the boiling experimental results and concernsthe effect of these mechanism. In this study, a heat flux of up to 4X parameters on critical heat flux and nucleate boiling. 107 kcal/m2-hr could be obtained in steady-state The boiling curve at high subcooling was not separated condition over the entire range of superheat 10- clearly into nucleate, transition and film boiling re- 800°C, by using a heated surface with a small diameter gimes. Heat flux was increased gradually over the of 1.5 to 2.0mm. Use of such a small diameter was entire range as superheat rose. necessary because it was very difficult experimentally The entire range is divided into three heat transfer to remain a high heat flux above 107 kcal/m2-hr in regions which may be hypothesized to exist in nu- steady-state condition by using a heated surface with cleate boiling. diameter above 2.0 mm.However, a heated surface 1. Experimental Apparatus and Procedure of 10 mmdia. was used for subcooled pool boiling. The effect of heated surface diameter on the boiling Figure 1 shows the experimental apparatus for the impinging jet, where high heat flux nucleate boiling Received May 4, 1979. Correspondence concerning this article should be addressed to Y. Miyasaka. Y. Owase is now with Kobe Steel Co., Ltd., of subcooled water was generated on a heat transfer Osaka 541. surface which was fixed on the copper heat conductor VOL. 13 NO. 1 1980 29 the top of the conical copper block and used to con- duct heat to the boiling surface. The base of the conical copper block was finished to 25 mmdia. and a carbon plate of thickness 2 mmwas placed on it in order to obtain radiant energy efficiently. The ceram- ic fiber heat insulator KAOWOOLwas packed tightly around the copper cylinder and conical cop- per block to reduce heat losses. This heat insulator possessed the function of the receiver of melting cop- per as well. Copper-constantan thermocouples of 0.1 mmdia. were used to measure temperature. The thermo- couples were calibrated over a wide temperature range of 100 to 900°C. Two constantan wires of 0.1 mm dia. were attached to the surface of the 1.5 mm-dia. copper cylinder by spot welding, one located 1.0 mm, Fig. 1 Experimental apparatus for impinging jet the other 2.0mm below the boiling surface. A copper wire of0.1 mmdia. was placed in a 0.5 mm-dia. hole drilled into the conical copper block and was stuffed with copper chips. The temperature indicated by these thermocouples was used as the average temperature in a cross section of the copper cylinder and heat flux was measured by calculations based on Fourier's equation for steady- state heat flow. Temperature of the boiling surface was measured by extrapolating the temperatures con- sidering the thickness of 0.05 mmof platinum foil. All the thermoelectric forces were recorded on a gal- vanograph through an attenuator and a changing- over switch. Fig. 2 Main part of apparatus for impinging jet The platinum foil attached on the copper cylinder was formed into a circular fin. The edge of the plati- by the diffusion-bonding method. This surface was numcircular fin was soldered to the brass plate to made of a 0.05mm thickness platinum foil. Dif- bridge the gap, leaving about 5 mmbetween copper fusion-bonding was achieved by keeping the tempera- cylinder and brass plate. Epoxy resin was used to ture of the contact face between platinum and copper prevent leakage of water at the outer edge of the brass at about 600°C for twenty-four hours in an electric plate. furnace filled with argon gas. The heat flux measured with the boiling surface The radiant energy of a molybdenumheater, being covered with Teflon rod showed that the heat losses heated by alternating current, was transferred to the through the platinum fin and the side of the copper end of the copper heat conductor. The a. c. power cylinder were negligible comparedto the rate of heat input was controlled with a 10-KVA adjustable transfer through the boiling surface. transformer. The furnace was filled with hydrogen Figure 3 shows the experimental apparatus for sub- gas in order to prevent the molybdenumheater from cooled pool boiling. Figure 4 shows the detailed oxidation. main part of the apparatus. The furnace used for A two-dimensional water jet was impinged upward subcooled pool boiling was identical to that shown in vertically on the heat transfer surface being standed Fig. 1. A 2.0mm-dia. copper cylinder, 5mm long, upside down in order to prevent the heater from adhe- was set facing upward and the platinum boiling sion of melting copper. surface was attached to it by the diffusion-bonding The test water was pumpedup to a height of about method. Furthermore, two boiling surfaces (3 mm 15 mand poured into the storage tank. The tempera- dia., 10 mmdia.) were used to investigate the effect of ture of the waterjet measured at the outlet of the noz- diameter on the boiling curves. Three 0.1 mm-dia. zle was kept constant at about 15°C. Figure 2 shows constantan wires were attached to the side of the cop- the details of the main part of the apparatus. A 1.5 per cylinder by spot welding. The copper wire of mm-dia. copper cylinder, 3 mmlong, was attached to 0.1 mmdia. was attached in muchthe same way as 30 JOURNAL OF CHEMICAL ENGINEERING OF JAPAN in Fig. 1. In the case of the 10mmdia. boiling sur- face, further, three constantan wires of 0.1 mmdia. isolated in a glass tube were fixed by spot welding in 0.5 mm-dia. holes drilled into the center of the copper cylinder with separation distance 1.0 mmbelow the heated surface. The test liquid, about ten liters of water, was placed into the boiling vessel so that the water level was about 250 mmabove the heated surface. The liquid tem- perature was measuredby time-interpolation of the temperatures at the beginning and end of the run. The maxmumvariation of liquid temperature from start to end of run was found to be about 10°C. The heated surface used in this work was cleaned with a 5/0 emery paper and acetone before each ex- perimental run. The power input to the molybdenum heater was increased very slowly. After a steady- Fig. 3 Experimental apparatus for subcooled state condition was reached, as indicated by tempera- pool boiling ture measurement, experimental data were taken. Each experimental run required about eight hours. 2. Boiling Curve 2. 1 Subcooled pool boiling curve Heat flux vs. superheat data measuredin subcool- ing 85°C at atmospheric pressure are plotted in Fig. 5. At a heat flux of about 106kcal/m2-hr, violent nucleate boiling on the heated surface was observed. The vapor generated at the active sites on the heated Fig. 4 Main part of apparatus for subcooled pool surface was in the form of discrete bubbles of 0.1 mm boiling dia., and was condensed immediately. As the tempera- ture of the heated surface was raised, heat flux increas- ed. Though the data showed scatter in some degree, these data appeared as an extension of the ordinary high heat flux saturated pool boiling curve at atmos- pheric pressure.
Load more

Recommended publications
  • The Mechanism of Nucleate Pool Boiling Heat Transfer to Sodium and the Criterion for Stable Boiling
    THE MECHANISM OF NUCLEATE POOL BOILING HEAT TRANSFER TO SODIUM AND THE CRITERION FOR STABLE BOILING Isaac Shai January 1967 DSR 76303-45 Engineering Projects Laboratory Department of Mechanical Engineering Massachusetts Institute of Technology Contract No. AT(30-1)3357,A/3 ENGINEERING PROJECTS LABORATORY NGINEERING PROJECTS LABORATOR 4GINEERING PROJECTS LABORATO' 1INEERING PROJECTS LABORAT 'NEERING PROJECTS LABORK 'EERING PROJECTS LABOR ERING PROJECTS LABO 'RING PROJECTS LAB' ING PROJECTS LA iG PROJECTS L PROJECTS PROJECT 7 R.OJEC DSR 76303-45 MECHANISM OF NUCLEATE POOL BOILING HEAT TRANSFER TO SODIUM AND THE CRITERION FOR STABLE BOILING Isaac Shai Atomic Energy Commis sion Contract AT(30-1)3357, A/3 1in1.MEHEIIMIjhh 111311911Hh''1111d,, " , " " ABSTRACT A comparison between liquid metals and other common fluids, like water, is made as regards to the various stages of nucleate pool boiling. It is suggested that for liquid metals the stage of building the thermal layer plays the most significant part in transfer heat from the solid. On this basis the transient conduction heat transfer is solved for a periodic process, and the period time is found to be a function of the degree of superheat, the heat flux, and the liquid thermal properties. A simplified model for stability of nucleate pool boiling of liquid metals has been postulated from which the minimum heat flux for stable boiling can be found as a function of liquid-solid properties, liquid pressure, the degree of superheat, and the cavity radius and depth. Experimental tests with sodium boiling from horizontal sur- faces containing artificial cavities at heat fluxes of 20, 000 to 300, 000 BTU/ft hr and pressures between 40 to 106 mm Hg were obtained.
    [Show full text]
  • Nucleate-Boiling Heat Transfer to Water at Atmospheric Pressure
    Scholars' Mine Masters Theses Student Theses and Dissertations 1966 Nucleate-boiling heat transfer to water at atmospheric pressure H. D. Chevali Follow this and additional works at: https://scholarsmine.mst.edu/masters_theses Part of the Chemical Engineering Commons Department: Recommended Citation Chevali, H. D., "Nucleate-boiling heat transfer to water at atmospheric pressure" (1966). Masters Theses. 2971. https://scholarsmine.mst.edu/masters_theses/2971 This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. NUCLEATE-BOILING HEAT TRANSFER TO WATER AT ATMOSPHERIC PRESSURE BY H. D. CHEV ALI - 1 &J '-I 0 ~~ A THESIS submitted to the faculty of THE UNIVERSITY OF MISSOURI AT ROLLA in partial fulfil lment of the requirements for the Degree of MASTER OF SCIENCE IN CHEMICAL ENGINEERING Roll a, Missouri 1966 Approved by / (Advisor ) ii ABSTRACT The purpose of this investigation was to study the hysteresis effect, the effect of micro-roughness and orientation of the heat-trans­ fer surface, and the effect of infra-red-radiation-treated heat-transfer surfaces on the nucleate-boiling curve. It has been observed that there exists no hysteresis effect for water boiling from a cylindrical copper surface in the nucleate-boiling region over the range studied. The nucleate-boiling curve has been found to be independent of micro-roughness and orientation of the heat­ transfer surface. There was no detectable change in the nucleate-boil­ ing characteristics of the heat-transfer surface when the surface was treated with infra-red radiation.
    [Show full text]
  • Nucleate Boiling Heat Transfer
    ECI International Conference on Boiling Heat Transfer Florianópolis-SC-Brazil, 3-7 May 2009 NUCLEATE BOILING HEAT TRANSFER J. M. Saiz Jabardo Escola Politécnica Superior, Universidade da Coruña, Mendizabal s/n Esteiro, 15403 Ferrol, Coruña, Spain [email protected] ABSTRACT Nucleate boiling heat transfer has been intensely studied during the last 70 years. However boiling remains a science to be understood and equated. In other words, using the definition given by Boulding [2], it is an “insecure science”. It would be pretentious of the part of the author to explore all the nuances that the title of the paper suggests in a single conference paper. Instead the paper will focus on one interesting aspect such as the effect of the surface microstructure on nucleate boiling heat transfer. A summary of a chronological literature survey is done followed by an analysis of the results of an experimental investigation of boiling on tubes of different materials and surface roughness. The effect of the surface roughness is performed through data from the boiling of refrigerants R-134a and R-123, medium and low pressure refrigerants, respectively. In order to investigate the extent to which the surface roughness affects boiling heat transfer, very rough surfaces (4.6 µm and 10.5 µm ) have been tested. Though most of the data confirm previous literature trends, the very rough surfaces present a peculiar behaviour with respect to that of the smoother surfaces (Ra<3.0 µm). INTRODUCTION Nucleate boiling is considered by some as an “old” science due to its exhaustive study during the last eighty years.
    [Show full text]
  • Prediction of Critical Heat Flux (CHF) for Vertical Round Tubes with Uniform Heat Flux in Medium Pressure Regime
    Korean J. Chem. Eng., 21(1), 75-80 (2004) Prediction of Critical Heat Flux (CHF) for Vertical Round Tubes with Uniform Heat Flux in Medium Pressure Regime W. Jaewoo Shim† and Joo-Yong Park Department of Chemical Engineering, Dankook University, Seoul 140-714, Korea (Received 2 July 2003 • accepted 8 November 2003) Abstract−The description of critical heat flux (CHF) phenomena under medium pressure (10 bar≤P≤70.81 bar) regime is complex due to the large specific volume of vapor and the effect of buoyancy that are inherent in the con- ditions. In this study, a total of 2,562 data points of CHF in uniformly heated round vertical tube for water were collected from 5 different published sources. The data consisted of the following parameter ranges: 93.7≤G (mass ≤ 2 ≤ ≤ ≤ ≤ ≤ ≤ 2 flux) 18,580 kg/m s, 0.00114 D (diameter) 0.03747 m, 0.008 L (length) 5 m, 0.26 qc (CHF) 9.72 MW/m , and −0.21≤L (exit qualities)≤1.09. A comparative analysis is made on available correlations, and a new correlation is presented. The new CHF correlation is comprised of local variables, namely, “true” mass quality, mass flux, tube diameter, and two parameters as a function of pressure only. This study reveals that by incorporating “true” mass quality in a modified local condition hypothesis, the prediction of CHF under these conditions can be obtained quite accurately, overcoming the difficulties of flow instability and buoyancy effects. The new correlation predicts the CHF data are significantly better than those currently available correlations, with average error 2.5% and rms error 11.5% by the heat balance method.
    [Show full text]
  • Experimental Study on Critical Heat Flux Behavior in Single Fuel Pin with and Without Wire Spacer
    EXPERIMENTAL STUDY ON CRITICAL HEAT FLUX BEHAVIOR IN SINGLE FUEL PIN WITH AND WITHOUT WIRE SPACER Dan Tri LE*, Noriaki IN ABA** and Minoru TAKAHASHI** *Department of Nuclear Engineering, Tokyo Institute of Technology Nl-18, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8550, Japan [email protected]. ac .j p **Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology Nl-18, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8550, Japan inaba@2phase .nr.titech. ac.j p [email protected] Abstract: Light water reactor could have fast neutron spectrum with high conversion ratio nearly equal unity by using tight lattice fuel assembly with wire spacer. Besides, the critical heat flux (CHF) data base for grid spacer has a great quantity of studies but it is not in case of wire type. In order to investigate coolability in tight lattice core in boiling water reactor (BWR), an experiment of critical heat flux (CHF) was conducted using single pin flow channels with a heater pin with and without wire. We determined the critical heat flux for this system by varying the inlet temperature from 333 to 373 K and mass fluxes from 200 to 700 kg/m1 2s and the pressure was atmospheric pressure. The result show the CHF data in two-phase flow condition base on inlet and outlet condition in both case of heater pin with and without wire. The CHF values were higher with wire than without wire due to the effect of wire and spiral flow. Keywords: Critical Heat Flux, Tight Lattice, Two-phase Flow, Wire Spacer.
    [Show full text]
  • Critical Heat Flux
    International Journal of Heat and Mass Transfer 43 (2000) 2573±2604 www.elsevier.com/locate/ijhmt Critical heat ¯ux (CHF) for water ¯ow in tubesÐI. Compilation and assessment of world CHF data David D. Hall, Issam Mudawar* Boiling and Two-Phase Flow Laboratory, School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, USA Received 29 September 1998; received in revised form 24 May 1999 Abstract The nuclear and conventional power industries have spent enormous resources during the past ®fty years investigating the critical heat ¯ux (CHF) phenomenon for a multitude of pool and ¯ow boiling con®gurations. Experimental CHF data form the basis for the development of correlations and mechanistic models and comparison with them is the sole criterion for a reliable assessment of a correlation or model. However, experimental CHF data are rarely published, remaining in the archives of the authors or in obscure technical reports of an organization. The Purdue University-Boiling and Two-Phase Flow Laboratory (PU-BTPFL) CHF database for water ¯ow in a uniformly heated tube was compiled from the world literature dating back to 1949 and represents the largest CHF database ever assembled with 32,544 data points from over 100 sources. The superiority of this database was proven via a detailed examination of previous databases. A point-by-point assessment of the PU-BTPFL CHF database revealed that 7% of the data were unacceptable mainly because these data were unreliable according to the original authors of the data, unknowingly duplicated, or in violation of an energy balance. Parametric ranges of the 30,398 acceptable CHF data were diameters from 0.25 to 44.7 mm, length-to-diameter ratios from 1.7 to 2484, mass velocities from 10 to 134,000 kg m2 s1, pressures from 0.7 to 218 bars, inlet subcoolings from 0 to 3478C, inlet qualities from 3.00 to 0.00, outlet subcoolings from 0 to 3058C, outlet qualities from 2.25 to 1.00, and critical heat ¯uxes from 0.05 Â 106 to 276 Â 106 Wm2.
    [Show full text]
  • Heat and Mass Transfer: Fundamentals and Applications 5Th Edition Download Free
    HEAT AND MASS TRANSFER: FUNDAMENTALS AND APPLICATIONS 5TH EDITION DOWNLOAD FREE Yunus A Cengel | 9780077654764 | | | | | ISBN 13: 9780073398181 Noting that the heat transfer area in this case is A 2rL and the thermal conductivity is constant, the one-dimensional transient heat conduction equation in a cylinder becomes 1 r r. The density of the cylinder is and the specific heat is c. The topic of critical heat flux is covered in Chap ter 10 Boiling and Condensation. Taking the positive direction of x to be from the inner surface to the outer surface, the correct Heat and Mass Transfer: Fundamentals and Applications 5th edition for the convection boundary condition is a k dT 0 dx Heat and Mass Transfer: Fundamentals and Applications 5th edition k b k h T 0 T dT 0 dx Answer a k 1 1 T hT 1 1 dT L dx 2 d k dT L dx T L T h 2 2 Heat and Mass Transfer: Fundamentals and Applications 5th edition h T 2 1 e None of them 2 dT 0 h T1 0 T 1 dx Consider steady one-dimensional heat conduction through a plane wall, a cylindrical shell, and a spherical shell of uniform Heat and Mass Transfer: Fundamentals and Applications 5th edition with constant thermophysical properties and no thermal energy generation. I have taken their services earlier for textbook solutions which helped me to score well. Properties The Heat and Mass Transfer: Fundamentals and Applications 5th edition surface has an absorptivity of 0. The total rate of heat transfer from the black ball is a W.
    [Show full text]
  • Thermal Hydraulics of Water Cooled Divertors
    GA–A23476 THERMAL HYDRAULICS OF WATER COOLED DIVERTORS by C.B. BAXI OCTOBER 2000 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. GA–A23476 THERMAL HYDRAULICS OF WATER COOLED DIVERTORS by C.B. BAXI This is a preprint of a paper presented at the 21st Symposium on Fusion Technology, September 11–15, 2000 in Madrid, Spain and to be published in Fusion Design and Engineering. Work supported by General Atomics IR&D Funds GA PROJECT 4437 OCTOBER 2000 C.B. BAXI THERMAL HYDRAULICS OF WATER COOLED DIVERTORS ABSTRACT Divertors of several new machines, such as JT-60SU, FIRE, SST-1, ITER-RC and KSTAR, are water-cooled. This paper examines critical thermal hydraulic issues associated with design of such divertors. The flow direction of coolant in the divertor can be either toroidal or poloidal. A quantitative evaluation shows that the poloidal flow direction is preferred, because the flow rate and pumping power are about an order of magnitude smaller compared to the toroidal flow direction.
    [Show full text]
  • A New Approach to Predicting Departure from Nucleate Boiling (DNB) from Direct Representation of Boiling Heat Transfer Physics
    A new approach to predicting Departure from Nucleate Boiling (DNB) from direct representation of boiling heat transfer physics by Etienne Demarly B.S., Engineering, École supérieure d’électricité (Supélec), 2011 M.S., Engineering, École supérieure d’électricité (Supélec), 2012 M.S., Nuclear Engineering, Institut national des sciences et techniques nucléaires (INSTN), 2013 SUBMITTED TO THE DEPARTMENT OF NUCLEAR SCIENCE AND ENGINEERING IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN NUCLEAR SCIENCE AND ENGINEERING AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY February 2020 ©2020 Massachusetts Institute of Technology All rights reserved. Author: Etienne Demarly Department of Nuclear Science and Engineering January 3, 2020 Certified by: Emilio Baglietto, Ph.D. Associate Professor of Nuclear Science and Engineering Thesis Supervisor Certified by: Jacopo Buongiorno, Ph.D. TEPCO Professor of Nuclear Science and Engineering Thesis Reader Certified by: John H. Lienhard V, Ph.D. Abdul Latif Jameel Professor of Mechanical Engineering Thesis Reader Accepted by: Ju Li, Ph.D. Battelle Energy Alliance Professor of Nuclear Science and Engineering and Professor of Materials Science and Engineering Department Committee on Graduate Students 2 A new approach to predicting Departure from Nucleate Boiling (DNB) from direct representation of boiling heat transfer physics by Etienne Demarly Submitted to the Department of Nuclear Science and Engineering on January 3, 2020 in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Nuclear Science and Engineering Abstract Accurate prediction of the Departure from Nucleate Boiling (DNB) type of boiling crisis is essential for the design of Pressurized Water Reactors (PWR) and their fuel.
    [Show full text]
  • Analysis of the DNB Ratio and the Loss-Of- Flow Accident (LOFA) of the 3 MW TRIGA MARK 11 Research Reactor
    BDO410004 INTERN,.,IL REPORT INST-90IRPED-22, MA Y 2003 Analysis of the DNB ratio and the Loss-of- Flow Accident (LOFA) of the 3 MW TRIGA MARK 11 Research Reactor M. Q. Huda, M. S. Mahmood, T. K. Chakrobortty, M. Rahman and M. M. Sarker REACTOR PHYSICS AND ENGINEERING DIVISION (RPED) INSTITUTE OF NUCLEAR SCIENCE TECHNOLOGY ATOMIC ENERGY RESEARCH ESTABLISHMENT GANAKBARI, SAVAR, GPO BOX 3787, DHAKA-1000 BANGLADESH ,q! 101- 9mWfw BANGLADESH ATOMIC ENERGY COMMISSION INST-90/RPED-22 CONTENTS Page 1. Introduction 1 2. Analysis of DNB Ratio 1 2.1. Effect of Operating Power 3 2.2. Effect of the Flow Rate 3 2.3. Effect of the Hot-Rod Factor 3 2.4. Effect of the Inlet Temperature 4 3. Loss-of-Flow Accident (LOFA) Analysis 4 3.1. Relative Power and Flow during LOFA 4 3.2. Fuel Temperature Distribution during LOFA 4 3.3. Occurrence of Flow Reversal 5 4. Conclusions 5 5. Acknowledgments 6 6. References 6 INST-90/RPED-22 ABSTRACT The PARET code was used to analyze two most important thermal hydraulic design parameters of the 3 MW TRIGA MARK research reactor. The first design parameter is the DNB (departure from nucleate boiling) ratio, which is defined as the ratio of the critical heat flux to the beat flux achieved in the core and was computed by means of a suitable correlation as defined in PARET code. The reactor core should be designed so as to prevent the DNBR from dropping below a chosen value under a high heat flux transient condition for the most adverse set of mechanical and coolant conditions.
    [Show full text]
  • Two Phase Flow Simulation for Subcooled Nucleat Boiling Heat Transfer Calculation in Water Jacket of Diesel Engine
    Two Phase Flow Simulation for Subcooled Nucleat Boiling Heat Transfer Calculation in Water Jacket of Diesel Engine A. Mohammadi* Iran Khodro Powertrain Company Tehran, Tehran, Iran M. Yaghoubi Professor of Mechanical Engineering in Shiraz University Shiraz, Iran Corresponding Author* Received: Dec. 18,2011 Accepted in revised form: Feb. 14,2011 Abstract Basic understanding of the process of coolant heat transfer inside an engine is an indispensable prerequisite to devise an infallible cooling strategy. Coolant flow and its heat transfer affect the cooling efficiency, thermal load of heated components, and thermal efficiency of a diesel engine. An efficient approach to studying cooling system for diesel engine is a 3D computational fluid dynamics (CFD) calculation for coolant jacket. Therefore, computer sim- ulation can analyze and consequently optimize cooling system performance, including complex cooling jacket. In Downloaded from engineresearch.ir at 3:59 +0330 on Monday October 4th 2021 this paper a computational model for boiling heat transfer based on two-phase Mixture model flow is established. Furthermore, the phenomenon of nucleate boiling, its mathematical modeling, and its effect on heat transfer is discussed. Besides, the static, total pressure, velocity and stream lines of the flow field, heat flux, heat transfer coef- ficient and volume fraction of vapor distribution in the coolant jacket of a four-cylinder diesel engine is computed. Also, comparison between experimental equation (Pflaum/Mollenhauer) and two-phase Mixture model for boiling heat transfer coefficient is done and good agreement is seen. In conclusion, it is observed that at high operating temperatures, nucleate boiling occurs in regions around the exhaust ports.
    [Show full text]
  • Saturated Nucleate Boiling with HFE-7100 on a Plain Smooth Copper Surface
    Proceedings of the 5th World Congress on Momentum, Heat and Mass Transfer (MHMT'20) Lisbon, Portugal Virtual Congress – October 2020 Paper No. ICMFHT 123 DOI: 10.11159/icmfht20.123 Saturated Nucleate Boiling with HFE-7100 on a Plain Smooth Copper Surface Xiaoguang Fan1，2, Mohamed M. Mahmoud2,3, Atanas Ivanov2, Tassos G. Karayiannis2 1Shenyang Agriculture University 120 Dongling Rd. Shenhe District, Shenyang, China [email protected] 2Brunel University London UB8 3PH, London, UK [email protected]; [email protected]; [email protected] 3Faculty of Engineering, Zagazig University, Zagazig, Egypt, 44519 [email protected] Abstract - Pool boiling is one of the main modes of heat transfer in many industrial applications. Therefore, the pool boiling heat transfer performance of various surfaces/geometries and the establishment of reliable predictive correlations has received a lot of attention from laboratories across the world. Visualization and heat transfer measurements of pool boiling using hydrofluoroether HFE-7100 as the working fluid on a plain smooth copper surface are described in this paper. The polished boiling surface had an average surface roughness of 0.019 μm. The saturated pressure ranged from 0.7 to 2 bar. The saturation pressure was found to affect the number of active bubble nucleation sites at a given temperature difference between the wall and the saturation temperature, delayed the formation of bigger bubbles and affected the pool boiling heat transfer. Starting with the lower pressure of 0.7 bar, the heat transfer coefficient increased by an average of 24%, 49% and 60% for saturated pressure of 1.0, 1.5 and 2 bar respectively.
    [Show full text]