NUMERICAL STUDY AND THERMAL PERFORMANCE OF THE FLAT PLATE SOLAR AIR HEATERS WITH AND WITHOUT THERMAL STORAGE

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1 ARPN Journal of Engineering and Alied Sienes 6-1 Asian Resear Publising Network (ARPN). All rigts reserved. NUMERICAL STUDY AND THERMAL PERFORMANCE OF THE FLAT PLATE SOLAR AIR HEATERS WITH AND WITHOUT THERMAL STORAGE P. T. Saravanakumar 1, K. Mayilsamy and M. Moanraj 3 1 Deartment of Meanial Engineering, Dr. Maalingam College of Engineering and Tenology, Pollai, Tamil Nadu, India Deartment of Meanial Engineering, Institute of Road and Transort Tenology, Erode, Tamil Nadu, India 3 Deartment of Meanial Engineering, Info Institute of Engineering, Coimbatore, India tsfd@gmail.om ABSTRACT Te eat transfer arateristi and erformane of te flat late air eater wit and witout termal storages are studied exerimentally. Te matematial models desribed tat te eat transfer of te late solar air eater are derived from te energy equation. Te imliit metod of finite differene seme is emloyed to solve tese models. Te effet of te termal ondutivity of te termal storage on te eat transfer arateristi and erformane is onsidered. Te results obtained from te model are validated by omarison wit exerimental data. Tere is a reasonable agreement between te resent model and exerimental data. Keywords: flat late solar air eater, termal storage, erformane. 1. INTRODUCTION To obtain maximum amount of solar energy of minimum ost te flat late solar air eaters wit termal storage ave been develoed. Solar air eater is tye of solar olletor wi is extensively used in many aliations su as residential industrial and agriultural fields. Te eat transfer arateristis of solar air eater ave been widely studied. Ve and lin [1] teoretially and exerimentally studied te effet of olletor aset ratio of te olletor on tat late uward baffled solar air eaters. Fat [] studied te erformane of te simle design solar air eater. Te onventional flat late absorber is resented by a set of tubes filled wit a termal energy average material org [3] redited te termal erformane of four ommon tyes of single ass solar air eater. Yadav et al., [4] analyzed te arametri studied of a susended flat late solar air eater. Aonad et al., [5] investigated a aked bed solar air eater. Te effet of tese arameters on te termal erformane as been investigated and te results ave been omared wit tose flat late olletors. Al Kamil and Al - Garab [6] exerimentally and teoretially studied te effet of various arameters su as temerature, solar intensity and air flow rate on te erformane of a flat late solar air eater. Ekeukwu and Norton [7] reviewed te various design and te erformane evaluation teniques of flat late solar energy air eating olletor for low temerature solar energy ro drying aliations. Gao et al., [8] numerially studied in natural onvetion inside te annel between te flat late solar over and te sine wave absorber in a ross orrugated solar air eater. Reently Naon and Kongtragoel [9] alied te matematial model for rediting te eat transfer arateristi and erformane of te various onfiguration of flat late solar air eater. P. N. Sarsavadia [1] as develoed a solar assisted drier and evaluation of energy requirement for te drying of onion. V. Sanmugam and E. Natarajan [11] onduted exerimental of regenerative desiant integrated solar drier wit and wit out refletive mirror, Bukola et al., [1] ave been studied evaluation of mixed mode solar drier. G. N. tiwari [13] analyzed te design arameter of a sallow bed solar ro drier wit refletor. N. S. Takur [14] as been studied eat transfer and funtion fator orrelation for aked bed solar air eater. T. W. Ceng [15] ave been studied influenes of reyle on erformane of baffled double - ass flat late solar air eater wit internal fins affeted A. Zamorodian et al., [16] ave been otimized a semi ontinuous solar drier for ereals. Sared Kumar and R. P. Saini onduted CFD based erformane analysis of a solar air eater [17] dut rovided wit artifiial reougness. Hikmut Esen et al., [18] ave been develoed ANN and WNN aroaes for modeling of a solar air eater. Wenferng Gao et al., [19] onduted analytial and exerimental studies on te termal erformane of ross orrugated and flat late solar air eaters. S. Kumar and A. Augustus Leon [] ave been develoed matematial modeling and termal erformane analysis of unglazed transired solar olletors. As desribed above, tere are many studies on te eat transfer arateristis and erformane of te solar air eater wit different termal storage one still limited. Te objetive of tis aer is to study teoretially and exerimentally on te eat transfer arateristis and erformane of solar air eater wit and witout termal storage materials.. MATHEMATICAL MODELING Te basi ysial equations used to desribe te eat transfer arateristis are develoed onservation of energy. Te metod is based on tat of Naon and Kongtragool [1] wit te following assumtions. flow of air study. inside and outside orretive eat transfer oeffiient is onstant along te lengt of solar air eater. 467

2 ARPN Journal of Engineering and Alied Sienes 6-1 Asian Resear Publising Network (ARPN). All rigts reserved. termal ondutivity of te storage material is onstant along te lengt of solar air eater. For to glass over Iα = at ( Ta) + fl ( T Tf1) + rct, ( T) + rat, ( Ta) (1) Were I is te solar intensity, α is te absortivity of te glass over, a is te eat transfer oeffiient between te ambient and te glass, T is te glass over temerature, T is te absorber late temerature, Ta is te ambient temerature, T f is te fluid temerature in a annel and r, C and r,a are te relative eat transfer oeffiient between te glass over and te absorber late, te glass. Cover and ambient follows: r1,, a r1 σ[ T = [ T + T ][ T + T] = [1/ ε + 1/ ε 1]. For air stream + T a (1/ ε 1) ][ T + T a] (a) Witout termal storage materials m dt f 1. f 1 f 1 1 f 1 dx () (3) = ( T T ) + f ( T T ) (4) (b) Wit termal storage materials m dtf 1 d Tf1 = kt 1 ( 1) 1 ( ) f T Tf + f T Tf (5) dx dx. 1 Were m is te mass flow rate of fluid er unit widt, C is te seifi eat transfer oeffiient te glass over and working fluid and f1 is te eat transfer oeffiient between te glass over and working fluid and f1 is te eat transfer oeffiient between te absorber late and working fluid..3 For absorber late Iα. τ = ( T T ) +, ( T T ) +, ( T T ) (6). f1 f1 r r b b Were α te absortivity of te absorber late, τ is te transmitivity of te glass over. Figure-1. Solar air eater (A) witout (B) wit termal storage..4 For bottom late o = ( T T 1) + ( T T ) + v ( T T ) (7) f 1b b f rb b a b a Were v a is te overall eat transfer oeffiient, T b is bottom late temerature, K is te termal ondutivity of te termal storage material. 3. CALCULATION METHOD Te eat transfer arateristi of solar air eater for te model is desribed by equation (1) to (6). Te solar air an be divided into number setions as Figure-. Te alulation is erformed setion by setion along solar air eater lengt. In order to solve te model te onvetive eat transfer oeffiient for air flowing over te outside surfae of te to glass over and inside eat transfer oeffiient are needed. Te onvetive eat transfer oeffiient for air flowing over te outside surfae of te glass over is roosed by M dams follows: a = v (8) Were a is te onvetive eat transfer oeffiient and V is te wind veloity. Niles et al., [3] roosed onvetive eat transfer oeffiient in te annel as follows: N D = k =.333 Re Pr i e u (9) Were N u is Nusselt number, R e is te reynold number, P r is randtl number, D e is equivalene diameter of annel as follows: 4W. H D e (W + H ) = (1) Were W is te widt of solar air eater, H is te eigt of te annel. 468

3 ARPN Journal of Engineering and Alied Sienes 6-1 Asian Resear Publising Network (ARPN). All rigts reserved. absorber late temerature T, bottom late temerature Tb. Te eat transfer rate Q is alulated. Te alulation of working fluid temerature at te outlet of annel is omared wit te inlet working fluid temerature. If te differene wit in 1-6, te alulation is ended and not, omutations are reeated until onvergene is obtained. Figure-. Simulation aroa. In addition te solar air eater onfiguration and roerties of working fluid, as well as oerating onditions are also needed. Te imliit metod of finite seme is emloyed to solve tese models. Iteration roess is desribed as follows: Te outlet working fluid temerature is assumed. Equation (1) to (6) are solved simultaneously to obtain te glass temerature T, working temerature Tf, 4. RESULTS AND DISCUSSIONS In te following setions, results of eat transfer arateristi of te solar air eater wit and witout termal storage are resented, in order to validate te limited available exerimental date. Numerial alulations are earned out by emloying te values of te relevant arameters also taken into aount are as follows: w α =.95, ε =.8, τ =.94, α =.5, ε =.94, v= 1, andv= 3m/ s m k Figures 3 and 4 sow te variation of termal effiieny of solar air eater wit and witout termal storage. Witout Termal Stroage Materials Witout Termal Storage S ola r Inte ns ity Colletor Effiieny Colletor Ef f iien (a) (b) Temerature Outlet Witout Termal Storage () Temerature Otlt Figure-3. (a) Solar intensity, (b) Colletor effiieny and () Temerature outlet varying wit reset to time for solar air eater witout termal storage materials. 469

4 ARPN Journal of Engineering and Alied Sienes 6-1 Asian Resear Publising Network (ARPN). All rigts reserved Wit Termal Stroage Materials Gravel wit Iron Sras (a) Colletor Effiieny Wit Termal Storage Gravel wit Iron Sras (b) Colletor Effiieny Wit Termal Storage Gravel wit Iron Sras Temerature at olletor outlet Temerature outlet () Figure-4. (a) Solar intensity, (b) Colletor effiieny and () Temerature outlet varying wit reset to time for solar air eater witout termal storage materials. 5. CONCLUSIONS Tis study resents te matematial model for rediting te eat transfer arateristi and erformane of te air eater wit te termal storage material. Te solar air eater wit te termal storage material gives 5-1% iger olletor effiieny tan tat of witout termal storage material. Te termal ondutivity of termal storage material as signifiant effet o termal erformane of te solar air eater. Te model is validated by omaring wit exerimental data. Nomenlature A = area of solar air eater (m ) D e = equivalene diameter (m) a = eat transfer oeffiient between ambient and glass f = eat transfer oeffiient between fluid and glass f = eat transfer oeffiient between fluid and glass i = inside eat transfer oeffiient r, = radiative eat transfer oeffiient between glass and absorber r,a = radiative eat transfer oeffiient between glass and ambient I = solar intensity (W/m ) L = lengt of solar air eater (m) N u = Nusselt number TS = termal storage material R e = Reynold s number T b = bottom late temerature (K) T f = fluid temerature (K) U a = overall eat transfer oeffiient V= wind veloity (m/s) = olletor effiieny C = seifi eat of fluid (kj/kg K) H = eigt of annel (m) K ts = termal ondutivity of termal storage materials m = mass flow rate (kg/s) P r = Prandtl Number Q = eat transfer rate (W) T a = ambient temerature (K) T = glass temerature T = absorber late temerature W = widt of solar air eater (m) Greek symbols α = absortivity of glass τ = transmitivit of glass ε = emissivity of glass 47

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