International Journal of Energy Engineering 2012, 2(4): 138-144 DOI: 10.5923/j.ijee.20120204.05
Study of Selective Surface of Solar Heat Receiver
Fuad Mammadov
Azerbaijan State Oil Academy, Azerbaijan Republic, AZ1010, Baku city, D.Aliyeva 227
Abstract For increasing of solar heating energy plants’ absorbing possibility and reducing heat loss selective nano-covered surface application has great practical importance. In the investigation Cu+Ni+SiO2+Ni+SiO2 and Cu+Ni+ZnS content selective nano-covered surface’ usage in solar energy plants was studied. This content having high effectiveness was painted on the surface of the specific solar receiver. In comparison with the other selective surfaces this selective nano-covered surface supplies to keep its optical properties stable till T>500 temperature. New type solar receiver with the developed selective nano-covered surface was tested in natural condition and at the lab. In the paper the most necessary heat-energy parameters of this solar receiver were defined. ℃ Keywords Solar energy, selective surface, solar receiver, absorption
can’t completely interfere into the nano and micro sized 1. Introduction holes on the pipe. Finally surface of the nano sized holes stays beaming and is reflecting sun rays. Besides on the For obtaining high effectiveness in solar energy plants surface of the solar receiver made from the steel material in solar hear receiver was covered by the special selective layer such holes rust appears, that leads to the rapid destruction of on the surface. Such surfaces give opportunity to increase the selective cover[3]. maximal effectiveness of solar receiver in sun radiation exchange. Both the cost and the covering technology of the selective layers are too expensive that’s why its safety is 2. Analysis of selective surfaces necessary. Therefore vacuum layer is made around the solar receiver having selective cover, and then it is put into the Different selective covers (Cu, Ni, SiO, SiO2, Si3N4, TiO2, clear glass pipe. At the expense of vacuum layer selective Ta2O5, Al2O3, ZrO2, Nd2O3, MgO, MgF2, ZnS and SrF2) are surface has no relation with the air, convective heat loss used[4,5] in solar receivers. These layers are covered to the reduces to the minimum and the selective layer can be pro- surface on solar receiver in the form of one or more layers. tected from the atmosphere impact for a long time. The solar receivers having such selective surfaces are util- At present ray absorption ability of selective cover in solar ized mainly in the parabolic through concentrators. The receivers located in the focus of solar energy plants with high performance of a candidate solar absorber can be character- temperature maximally equals 0,94[1]. For effective photo ized by its solar absorptance and thermal emittance. Using thermal conversion solar receiver surface should have high Kirchoff’s law, spectral absorptance can be expressed in solar absorption (α) and low heat loss (ε) at the operational terms of total reflectance ρ (λ,θ) for opaque materials, temperature. The operational temperature ranges of these αλθ(,)= 1 − ρλθ (,) (1) materials for solar energy application is divided into low and temperature (T<100 ), medium temperature (100
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λ −∞ max [1− ρλ (,T )] B (, λ Td ) λ trinsic absorbers use a material having intrinsic properties ∫λ − min 0 that result in the desired spectral selectivity. Semiconduc- ε =()T = (3) σT 4 tor-metal tandems absorb short wavelength radiation be- where σ =5,6696 ⋅ 10−8Wm −− 24 K is the Stefan-Boltzmann cause of the semiconductor bandgap and have low thermal constant and BT(,λ ) is the spectral irradiance of a black- emittance as a result of the metal layer. Multilayer absorbers use multiple reflections between layers to absorb light and body curve from can be tailored to be efficient selective absorbers. Addition- c BT(,λ )= 1 (4) ally, selectively solar-transmitting coatings on a black- c2 () 5 λ body-like absorber are also used but are typically used in λ e T −1 low-temperature applications. These constructions are
8 42− 4 shown schematically in Figures 1 a-d, respectively, and are where c =3,7405 ⋅ 10 Wµ mm and c =1,43879 ⋅ 10 µmK which 1 2 discussed in greater detail below. are Planck’s first and second radiation constants, respec- tively. The actual performance of an absorber at high tem- peratures may not correspond to the calculated emittance. This is because small errors in measured ρ can lead to large errors in small values of ε[7]. In addition, for some materials the measured emittance data at two different temperatures may simply be different. For example, at λmax , the black- body wavelength maximum for a specific temperature,
λµmax ( )⋅=TK ( ) 2898( µ K ) (5) Emittance is a surface property and depends on the surface condition of the material, including the surface roughness, surface films, and oxide layers[8]. Coatings typically repli- cate to some degree the surface roughness of the substrate. Therefore to facilitate development, it is important to meas- ure the emittance of each coating-substrate combination as well as the uncoated substrate when developing a solar se- lective coating. Furthermore, selective coatings can degrade at high temperatures because of thermal load (oxidation), Figure 1. Schematic designs of four types of coatings and surface treat- high humidity or water condensation on the absorber surface ments for selective absorption of energy (hydratization and hydrolysis), atmospheric corrosion (pol- lution), diffusion processes (interlayer substitution), chemi- cal reactions, and poor interlayer adhesion[9,10]. Calculating 4. The Materials Used the emittance from spectral data taken at room temperature assumes that the spectral characteristics do not change with Titanium, zirconium, or hafnium metal carbides, oxides, increasing temperature. This is only valid if the material is and nitrides have a high degree of spectral selectivity. The group IV metal compounds are of the general formula invariant and does not undergo a phase change (as do some MCxOyNz, M=Ti, Zr, or Hf, and x + y + z <2. In these titanium containing materials), breakdown or undergo oxi- tandem absorber-reflector films, of the compositions studied, dation (as do paints and some oxide coatings) at higher substoichiometric compounds of TiNx, ZrNx, and ZrCxNy temperatures. It is important before using high-temperature (on silver) had the best combination of high solar absorp- emittance calculated from room temperature data, that the tance and low thermal emittance. The absorptance and calculated data is verified with high-temperature emittance emittance calculated from reflectance data are summarized measurements for each selective coating. The key for in Table 1[11]. TiNx and ZrNx had nearly identical optical high-temperature usage is low å, because the thermal radia- properties, but for HfNx the absorptance was lower and the tive losses of the absorbers increase proportionally by the emittance higher. ZrC was the best pure carbide film. Adding fourth power of temperature; therefore, it is important to carbon to form zirconium carbonitride (ZrCxNy) increased measure the emittance at the operating temperatures and the solar absorptance by 6%. Oxygen, either as suboxides conditions[7]. (TiOx and ZrOx) or substituted into the nitrides and carbo- nitrides (ZrOxNy or ZrCxOyNz) lowered absorptance and raised emittance. A notable exception was an oxidized Zr 3. Description of Absorber Types film with an absorption of 0.93. Solar absorptance was in- creased by 8% by replacing the aluminum reflective film Selective absorber surface coatings can be categorized with an ultrafine dendritic aluminum. Absorptance was also into six distinct types: a) intrinsic, b) semiconductor-metal increased by 5% by the addition of number of samples by tandems, c) multilayer absorbers, and d) selectively so- normal reflectance and total emittance measurements carried lar-transmitting coating on a blackbody-like absorber. In- out at elevated temperature. Depending on the sample, there
Fuad Mammadov: Study of Selective Surface of Solar Heat Receiver 140
was good agreement with room-temperature measurements Methods of combining the characteristics of controlled up to 400º-600˚C. The thermal stability of these tandem morphology with intrinsic selectivity deserve further inves- absorber-reflector films was studied, and several absorbers tigation. This work was discontinued in September 1976 and survived cumulative heating periods of 500 h in vacuum up was not resumed. Similar research in Japan appears to have to the maximum test temperature, 700 [12]. The addition metamorphosed into superconductivity work in 1982[16]. of a thin Al2O3 diffusion barrier improved the stability in air More recent research incorporated the selective properties of from 125 to 175 [13]. The stability℃ of the tandem films pores and created a temperature-stable (400 ), so- at high temperatures in vacuum was limited to the agglom- lar-selective coating with a void volume of 22%-26% de- eration of℃ the metal℃ reflective film, for silver about 350 . posited by reactive evaporation of Ti, Zr, and Hf ℃with ni- trogen and oxygen onto copper, molybdenum, or aluminum The use of thin layers of Cr2O3, Al2O3, SiO2, or other oxide under the metal has been found to stabilize the silver and℃ substrates with a SiO2 antireflective layer[17]. Solar ab- aluminum and inhibit agglomeration at high tempera- sorbers could be made by reactive sputtering the nitrides of tures[14]. Agglomeration has been inhibited at temperatures zirconium, yttrium, cerium, thorium, and europium (i.e., ZrN, up to 800 for one hour, but the limit of silver stability YN, CeN, TlN, and EuN), which are transparent in the in- achieved was about 500 [15,16]. The selective optical frared, abrasion resistant, inert, very hard, and stable at ℃ temperatures in excess of 500 for long periods of time[18]. properties of sputtered ZrCxNy on aluminum-coated oxi- dized stainless-steel are thermally℃ stable from room tem- A recent patent includes ZrN, TiN, HfN, CrN, or TixAl1-xN ℃ perature to 600 (likely in vacuum but was not speci- cermets in an Al2O3 dielectric matrix (patent includes TiO2, fied)[14]. Sputtered selective absorbers with the structure ZrO2, Y2O3, SiO2, Ta2O5, WO3, V2O5, Nb2O5, and CeO2) ℃ Al2O3/ZrCxNy/Ag have good optical selectivity with made by the sol-gel technique, where the liquid was applied
α/εC(325 )=0.91/0.05 at an operating temperature of 700 by spraying or spin coating and heat treated in air at 500 to in vacuum and 175 in air[17]. Sputtered ZrO /ZrC /Zr 600 [19]. Additionally, a thin surface film of metal oxyni- ℃ x x ℃ ℃ absorbers have α/ε(20 )=0.90/0.05 and are thermally sta- trides (niobium, tantalum, vanadium, zirconium, titanium, ℃ ble in vacuum on stainless℃ -steel and quartz substrates up to and molybdenum) can be made by coating a substrate with a 600 and 800 , respectively℃ [16]. “Raney nickel” type slurry of a metal halide in a liquid volatile carrier and con- alloys were prepared by co-sputtering nickel, zirconium, or verting the metal halide to a metal oxide or oxynitride by molybdenum℃ with℃ aluminum. After the aluminum was heating it with oxygen and nitrogen[18]. These materials etched out of the ZrAl film, a very fine open structure re- have some of the highest melting points in nature, with HfC 3 having the highest melting point at 3316˚C. The optical sulted that had a solar absorptance greater than 0.95 and a properties of these materials have a high degree of flexibil- calculated emittance at 327 of 0.29[15]. ity, and with further research, including replacing the stabi- lized silver with a more thermally stable reflective metal, Table 1. Composition and Properties℃ of Selected MCxOyNz absorbers could be a viable high-temperature absorber for the concen- Antireflective Absorbing Reflective 1 α ε (32701C ) trated solar power program[20]. layer layer layer
ZrOx Ag 0.72 0.42
TiOx Ag 0.80 0.067 5. Developement method of Solar
CrOx Ag 0.74 0.079 Receiver ZrN Ag 0.86 0.039 x For parabolic trough concentrator solar receiver was de- TiNx Ag 0.80 0.034 veloped which has a new selective nanosurface. Solar re- AlOx TiNx Ag 0.94 0.170 ceiver consists of cylindric pipe with D/d=132/128 mm
HfNx Ag 0.76 0.027 diameter and 1400 mm length. Beforehand high smooth ZrC Ag 0.81 0.075 surface on the pipe was obtained by the polishing machine. Then in the special oven it stays at 60-80 temperatures for ZrO N 2 Ag 0.93 0.071 x y a while (30-50 sec) for thermal processing and it is cooled. ZrCxNy Ag 0.88 0.040 By the specific equipment (SC-400 Precise℃ Coat) the selec- ZrCxNy Al 0.85 0.074 tive layer is covered on the pipe surface in dusting regim. 3 ZrCxNy Al 0.93 0.071 The content of the selective cover consists of Cu+Ni+SiO2+Ni+SiO2 and Cu+Ni+ZnS, its thickness is AlOx ZrCxNy Ag 0.91 0.048 0,013-0,058 nm. ZrO ZrC N Ag 0.64 0.014 x x y Hereupon, solar receiver is put into the clear glass. Inter- ZrCxOyNz Ag 0.66 0.020 stice between metal pipe and glass pipe is vacuumized 4 −4 ZrAl3 Ag 0.97 0.290 (P〈⋅ 5 10 mm.mercury column) . On the vacuum layer the 1 Numerical integration from normal reflectance data, AM2, high temperature forming on the solar receiver surface can’t 2 Sputtered Zr film “oxidized in hot air, 3 lose. Maximal limit of the temperature on the receiver sur- Ultra-fine dendritic aluminum, 2 4 “Raney” face was 422 at 1005 W/m solar radiation.
℃ 141 International Journal of Energy Engineering 2012, 2(4): 138-144
η 1,1
0,9
0,7
0,5
1 2 3 4 5 0,3
0,1 0 0 100 200 300 400 т, C 500
Figure 3. Dependence of the efficiency on the temperature of solar re- 2 Figure 2. Scanning Electron Microscope photomicrograph of selective ceiver selective nanocover for different solar radiations (1-200 Wt/m ; 2 2 2 2 nano surface texture 2-400 W/m ; 3-600 W/m ; 4-800 W/m ; 5-1000 W/m ) In comparison with the simple solar receiver, effective usage quantity of the ideal solar receiver is determined like 6. Calculation of Concentrator and Solar that:
Receiver System Efficiency ()η − ψ = ptc reac (8) ef ()η For solar receiver having parabolic trough concentrator ptc− reac ideal and selective nanocover efficiency is calculated like that: ∞ αλ(T )(⋅ r λ Td ) λ ∫ s sns s 7. Thermal-Energy Calculation of Solar ηη= 0 − ptc− reac R ∞ Receiver λλ ∫ r() Tds 0 For determining the efficiency of solar receiver having (6) ∞ new selective surface heat balance equations are looked ελ()()T⋅ rT λ d λ T ∫ sns sns through. At stationary regime for solar receiver heat balance −n()sns 4 0 equation will be so: T ∞ s λλ qqq= + (9) ∫ rT()sns d ab eff loss 0 Here,
Efficiency of solar receiver having ideal selective nano- qab =⋅ KKglass ⋅⋅ A s E g 2 cover will be so: - solar radiation W/m adsorbed by solar receiver; qeff - λ opt effective heat W/m2 absorbed by the heat carrier circling in r()λλ Tds 2 ∫ the internal pipe; qloss - the entire heat loss W/m from the ()ηη= 0 − pk− reac ideal R ∞ surface of solar receiver; K - concentration coefficient of r()λλ Td ∫ s solar energy; K glass - integral ray transmission coefficient of 0 (7) glass pipe wall; As - integral ray absorption of solar receiver; λopt 2 rT()λλ d Eg - solar radiation W/m falling on solar receiver surface. T ∫ sns −n()sns 4 0 If heat loss from solar receiver surface equals to the heat T ∞ s λλ loss from the glass pipe surface to the environment, then ∫ rT()sns d 0 complete heat loss can be determined: qq= += qq + q (10) Here, n - depletion coefficient of sun rays’ density on the loss irr. loss con irr .. glass con glass or definite points of the selective nano surface; Tsns - tempera- 44 ture of selective nano surface receiving sun rays; Ts aver- qloss=ες r0 () TT reac −+ glass age temperature of solar surface; rT()λ s - spectral quantity of λglass radiant flux density at Ts temperature of selective nanocover +()TTreac −= glass (11) dglass of the solar receiver; rT()λ sns spectral quantity of radiant rreac ln flux density at Tsns temperature of selective nanocover of the dr 44 solar receiver; αλs()T sns and ελ()Tsns - spectral adsorp- =εςglass ⋅0.(T glass −+ T a )( α glass a TT glass − a ) tion-irradiant ability mark of solar receiver selective nano- Here, q - heat losses W/m2 happened on solar receiver cover. irr. loss The efficiency indexes calculated by this method was surface by irradiance; qcon - possible convective heat loss 2 given at Figure 3. W/m between solar receiver and glass pipe; qirr. glass and
Fuad Mammadov: Study of Selective Surface of Solar Heat Receiver 142
qcon. glass irradiation from the glass pipe surface to the envi- these solar receiver effectiveness can be determined. ronment and heat losses W/m2 by convection; т, 0C 1 ε = 500 reac 11d 1 +−r ( 1) εεrd glass glass 400
- blackness rate of selective nanocover on the solar re- 2 300 ceiver. ε şüş - blackness rate of glass pipe. α glass. a - heat transfer coefficient W/m2 from glass pipe surface to the 2 4 200 environment (air); ς 0 - Stefan-Bolsman constant, W/m K ;
TTreac,, glass T a - temperatures of glass pipe and air and solar 100 receiver. dr and dglass - diameter of solar receiver and glass pipe. 0 2 0 200 400 600 800 1000 W/m 1200 q, W/m2 160 Figure 5. Dependence of solar receiver selective nanocover temperature 5 on solar radiation (1- by vacuum isolation, 2- by without vacuum isolation) 140 Table 2. Natural tests results of solar receiver having selective na- 120 no-covered surface (July-August, 2011) 4
100 Direct Average Average selective solar air wind nano-covered 3 Date Efficiency % 80 radiation, tempera speed, surface tem- W/m2 -ture, m/sec perature, 60 2 July 2011 ℃ ℃ 40 1 1 853 36 2,1 381 0,82 5 879 38 2,8 386 0,84 20 10 897 38,1 3,5 389 0,84 0 15 934 39 2,0 392 0,85 0 100 200 300 400 500 т, 0C 600 20 955 39 1,2 399 0,86 Figure 4. Dependence of heat losses from solar receiver surface on tem- 25 968 41 1,1 401 0,87 perature for several solar radiations (1-200 W/m2; 2-400 W/m2; 3-600 W/m2; 4-800 W/m2; 5-1000 W/m2) 30 913 40,4 1,5 390 0,85 August 2011 As seen from figure 4 by increasing the temperature on 1 889 39,6 1,4 388 0,84 solar receiver surface heat losses become greater. These 5 888 39,5 2,0 388 0,84 losses are usually great at high temperatures. The existence 10 835 39 1,8 380 0,82 of vacuum layer around solar receiver these losses happen by 15 802 38,6 2,4 378 0,81 irradiance. 20 754 36 3,3 375 0,79 By using equations for heat balance and heat losses of 25 721 35,8 3,8 372 0,79 solar receiver thermal efficiency can be determined: 30 695 33,7 3,5 369 0,77 q qq η =eff = ab− loss (12) t As seen from figure 5 vacuums isolation influences posi- KEgg KE tive on solar receiver effectiveness. Beginning from marks Using q and q for (9) and (11) formulas, the in- ab loss after 1000 W/m2 of solar radiation temperature stability dexes are out in the places: appears. At the same condition in the temperature curves on 44 εςr0 ()TT reac−+ glass solar receiver surface being studied at the expense of vacuum 2 isolation 105 (1100 W/m ) temperature difference has 1 λglass ηt=KA glass s − +−()TT (13) happened. kE d reac glass g glass At table 2 the℃ experiments; results carried out in 2011, on rreac ln dr July-August months have been given. Here on each month in For (13) using (11) formula: different days direct solar radiation, average air temperature, 44 average wind speed and temperature of selective nanocover 1 εςglass0 ()TT glass−+ a η =KA − (14) on solar receiver surface were measured and noticed. Due to t glass s kE +−α g glass. a()TT glass a the obtained results efficiency of solar receiver was calcu- The calculation of thermal efficiency depends on work lated. regime, work condition, contructive anf optic parameters of At figure 6 acccording to the natural climatic condition of solar receiver and glass pipe. Taking into consideration all Absheron peninsula dependence of average temperature of
143 International Journal of Energy Engineering 2012, 2(4): 138-144
selective nanocover on day hours was given during the ex- Scotland. pp. 452-455. periments realized on seasons. [3] F.F. Mammadov. Use of solar energy in Azerbaijan and modern solar energy plants, Progress, Baku, 2011, p.204. t, 0C 450 [4] R. B. Pettit, C. J. Brinker, and C. S. Ashley, “Sol-gel 400 double-layer antireflection coatings for silicon solar cells,” 350 Solar Cells, 15, 267 (1985). 300 250 [5] A. F. Pereev and N. P. Frolova, “Antireflecting coatings for 200 light-absorbing materials for the 0.4-5 μm spectral region,” 150 Sov. J. Opt. Technol., 41, 8, 453 (1974). 1 2 100 3 4 [6] C. Seiffert, T. Eisenhammer, M. Lazarov, R. Sizmann, and R. 50 Blessing, “Test facility for solar selective materials,” ISES 0 Solar World Congress, 2, 321 (1993). 7 9 11 13 15 17 19 hours 21 Figure 6. Dependence of solar receiver selective nanocover temperature [7] A. Brunotte, M. Lazarov, and R. Sizmann, “Calorimetric change on day hours due to the seasons. Here on the seasons 1- summer, measurements of the total hemispherical emittance of 2-autumn, 3-spring, 4- winter curves were given selective surfaces at high temperatures,” A. Hugot-Le Goff, C. G. Granqvist, C. M. Lampert, eds., SPIE, 1727, 149 (1992). As seen from the figure selective nanocover temperature [8] R. B. Pettit, “Total hemispherical emittance measurement begining from the morning hours of the day increases till the apparatus for solar selective coatings,” SAND-75-0079, 00 day time. At 14 reaches to peak rate, then the temperature Albuquerque, NM: Sandia National Laboratory, 1975. gradually decreases. These curves on each season during [9] S. Brunold, U. Frei, B. Carlsson, K. Möller, and,M. Köhl, 91/70-80 days have been determined by the experiment. “Accelerated life testing of solar absorber coatings: testing procedure and results,” Solar Energy, 68, 4, 313 (2000). [10] W. S. Duff and L. Hamasaki, “Experimental evaluation of 8. Discussion selective surfaces evacuated solar collectors,” R. Campbell-Howe, T. Cortez, and B. Wilkins-Crowder, eds., The technical parameters of the new selective nanocover: Proceedings of American Solar Energy Conference, ● High absorption of solar thermal energy α - 96>98% (American Solar Energy Society, Boulder, CO, 1998) p.345. typical 94% [11] R. Blickensderfer, “Metal oxycabonitride solar absorbers,” ● Low emittance of infra-red radiation ε = 4>10% typical Proc. DOE/DS7 Thermal Power Systems Workshop on 7% Selective absorber coatings, P. Call, ed,. SERI TP-31-061, ● Coefficient of thermal expansion 12.5 x 10-6 C Golden, CO: Solar Energy Research Institute, 1977, p. 371; R. These conclusions show that the developed solar receiver Blickensderfer, D. K. Deardorff, and R. L. Lincoln, “Spectral reflectance of TiN and ZrN films as selective solar absor- having selective nanocover has high effectiveness. So, ray x x bers,” Solar Energy, 19, 429 (1977); R. Blickensderfer, U.S. absorption ability is high, heat losses are scanty. Patent No. 4,098,956, 4 July 1978. [12] K. D. Masterson and B. O Seraphin, “Investigation of high temperature performance of thin film, solar-thermal energy 9. Conclusions converters,” Arizona Univ. Optical Science Center, Tuscon, While summarizing the final conclusion such decision AZ, (1976). was obtained that the developed solar receiver having selec- [13] D. M. Mattox and R. R. Sowell, “A survey of selective solar tive nanocover can be used at the following energy plants absorbers and their limitations,” Journal de Physique, C1, n1, absorbers: 42, (1981). ● Flat plate solar collectors for both hot water and hot air [14] H. Ihara, S. Ebiswa, and A. Itoh, “Solar-selective surface of type. zirconium carbide film,” Proc. 7th Int. Vac. Cong. and 3rd Int. ● Parabolic trough and parabolic type collectors. Conf. on Solid Surfaces, R. Dobrozensky, F. Ruderman, F. P. Viehbock, and A. Breth, eds., (1977) p. 1813. ● Vacuum tube type collectors. ● Passive heating systems. [15] Y. Noguchi, K. Naka, A. Isao, K. Nakumura, S. Sawada, T. ● A ‘Black’ body requiring low infra-red emittance. Tani, and S. Gonda, “Fabrication of ZrCx/Zr and Cr-CrOx films for practical solar selective absorption systems,” SPIE, 324, 124 (1982). [16] M. P. Lazarov and I. V. Mayer, U.S. Patent No. 5,670,248, 23 September 1997; M. P. Lazarov and I.V. Mayer, U S. Patent REFERENCES No. 5,776,556, 7 July 1998. [17] A. H. Lettington and C. Smith, U.S. Patent No. 5,723,207, 3 [1] J.A. Duffie, W.A. Beckman. Solar Energy Thermal Process. March 1998. Wiley, New York. 2006, p.928. [18] 197.C. Z. Deng, K. C. Tsai, and D. Ghantous, U.S. Patent No. [2] Mammadov F.F. Solar energy application for purification and 5,980, 977, 9 November 1999. treatment of oily waste in oil fields / Tenth World Renewable Energy Congress and Exhibition 2008, 19-25 July, Glasgow, [19] J. A. Thornton and J. A. Lamb, “Evaluation of cermet selec-
Fuad Mammadov: Study of Selective Surface of Solar Heat Receiver 144
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