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### 133 subhash presentation 1

1. 1. An Analytical Investigation on Thermal and Thermohydraulic Performance of Finned Absorber Solar Air Heater Presented by Dr. Prabha Chand Associate Professor Department of Mechanical Engineering National Institute of Technology, Jamshedpur – 831014 Jharkhand, India
2. 2. INTRODUCTION This paper deals with theoretical parametric analysis of finned absorber solar air heater. Two models of solar air heater one with rectangular fins and other with triangular fins has been developed. The fluid channel is formed by two transversely positioned fins attached on the absorber plate, bottom side thermally insulated and top surface of absorber subjected to uniform heat flux. The expression for collector efficiency factor and collector heat removal factor of such collector has been developed. Effects of mass flow rates on thermal performance have been presented and results are compared with flat plate air heaters.Further, the thermohydraulic performance parameter called “effective efficiency” has been employed and presented to express the net useful
3. 3. Mathematical Analysis Solar air heater with extended surface absorber
4. 4. Cont. Considering a slice of average width W and thickness dx at a distance x from inlet then the energy balance equations for the absorber plate, the bottom plate and the air flowing in between respectively can be written as S. W. dx = Ul W dx (Tp-Ta)+hfpWdx (Tp - Tf)+ 2Df dxηfhff (Tp-Tf)+hrWdx(Tp-Tb) (1) hr W dx (Tp-Tb) = hfb W dx (Tb-Tf)+UbW dx (Tb-Ta) (2) W  m C p dTf =hfp W dx (Tp - Tf)+ 2Df dx ηfhff (Tp- Tf)+ hfb W dx (Tb - Tf) L2 he is the effective heat transfer co-efficient and can be given as   2 D f ηf h ff he= h fp 1 +  W h fp     hr h fb  +  h +h  r fb    (3)
5. 5. Cont. F' is the collector efficiency factor and expressed as  Ul  F = 1 +   he  −1 ' For the heat transfer coefficient, the characteristic dimension used in the definitions of Nu and Re is the equivalent diameter de given by 4 (WL − ∂ f L f ) 4.Cross −sec tion area of a fin channel for de = Wetted perimeter of a fin channel = 2 (W + L ) rectangular fin f = 4 (WL −0.5 ∂ f L f ) 2 (W + ( 0.5 ∂ f ) 2 +( L f ) 2 ) for triangular fin
6. 6. Cont. The temperature distribution along the flow direction and collector heat removal factor can be expressed as S T −T −  F' U A  fo a U l =exp  l c L − S    mC T −T − p   fi a U a F R=  mC p AcU l [ (  1− exp − AcU l F ' / mC p )]
7. 7. Cont. The collector efficiency can be expressed as η=  mCp ( Tfo − Tfi ) I   mCp ∆T  =  I   where I = S (τα)e Here, the solar air heater works on an open cycle so the inlet temperature coincides with the ambient temperature and the above equation becomes η=  mC p ( Tfo − Ta ) I or η = G Cp∆T/I
8. 8. THERMOHYDRAULIC PERFORMANCE Thermohydraulic performance is the performance of the system that includes the consideration of thermal as well as hydraulic characteristics. The pumping performance of the collector in terms of the effective efficiency that taken into account the useful thermal gain and equivalent thermal energy that will be required to provide corresponding mechanical energy for overcoming friction power losses. Effective efficiency, ηe, of a solar air heater is given by, ηe = The useful energy gain is written as Qu = ṁ Cp(Tfo - Tfi) The net energy gain, Qn of the collector can be expressed as the different between the useful thermal energy gain, Qu, and the equivalent thermal energy required for producing the work energy necessary to overcome the pressure energy losses. This net energy can be written as Qn = Qu – Pm/Cf
9. 9. Cont. Cf is the conversion factor representing conversion from thermal energy to compression energy of the fan/blower imparted to air and is given as Cf = ηf .ηm .ηt .ηth where, ηf= Efficiency of fan. ηm = motor efficiency ηt= Efficiency of electrical transmission. ηth = thermal conversion efficiency of power plant. where Cm is the equivalent temperature drop due to friction. Cm = ∆P/Cfρ Cp Cm = equivalent temperature drop due to friction The effective temperature rise is given as; ∆Te = [(To - Ti) - Cm]
10. 10. Results And Discussions Effect of mass flow rate on collector efficiency factor Effect of mass flow rate on collector efficiency Factor
11. 11. Cont. Effect of mass flow rate on heat removal factor. Effect of mass flow rate on heat removal factor .
12. 12. Cont. Effect of mass flow rate on ∆T/I Effect of mass flow rate on ∆T/I
13. 13. Cont. Effect of mass flow rate on instantaneous efficiency efficiency Effect of mass flow rate on instantaneous
14. 14. Cont. Variation of pressure drop with mass flow rate Variation of pressure drop with mass flow rate
15. 15. Cont. Effect of mass flow rate on thermohydraulic and thermal efficiency Effect of mass flow rate on thermohydraulic and thermal efficiency
16. 16. CONCLUSIONS Considerable improvement in air temperature rise parameter (∆T/I) and efficiency of flat-plate solar air heater is obtained by providing rectangular and triangular fins on the absorber plate of solar air heaters. An enhancement of thermal efficiency in triangular finned and rectangular finned absorber is 32% and 34% reported respectively compared with flat-plate absorber solar air heater and this enhancement is a strong function of operating parameter and system parameter. However, any attempt to increase the heat transfer rate hence performance will , by the Reynolds Analogy, also result in an increase in pressure drop leading to an increase in the pumping power and hence there is a need to optimize the system .
17. 17. REFERENCE [1] BAA Yousef, NM Adam,( 2008)“Performance analysis for flat plate collector with and without S porous media” Journal of Energy in Southern Africa , Vol 19 No 4. [2] Hottel, HC., and Woertz, B.B., (1955) "Evaluation of flat plate solar collector performance", Trans. of the Conference on use of Solar Energy, Part I, Arizona, 74-104. [3] air Hüseyin Benli, (2012) “Experimentally derived efficiency and exergy analysis of a new solar heater having different surface shapes” Renewable Energy 50 ,58-67. [4] Duffice, J.A., and Backman, W.A., (1974)"Solar energy thermal processes", Jhon Wiley and Sons, New York. [5] Sukhatme, S.P. (1997), “Solar Energy: Principles of Thermal Collection and Storage “Tata McGraw Hill . [6] Blaine, F. Parker, (1981) "Derivation of efficiency and loss factor for solar air heaters", Solar Energy, 26, 27-32.
18. 18. Cont. [8] Kays, W.M. and London, A.L., "Compact heat exchangers", 2nd Ed., McGraw Hill, New York. [9] Sharma, S.P., Saini. J.S. and Verma, H.K., (1991) "Thermal performance of packed-bed solar air heaters", Solar Energy, Vol. 47, 2, 59-67. [10] Piao, Y., Hauptmann, E.G., and Iqbal, M., (1994) "Forced convective heat transfer in cross-corrugated solar air heaters", J. of Solar Energy Engineering, 116, 212-214. [11] Ho-Ming Yeh, Chii-Dong Ho and Chi-Yen Lin, (1998) "The influence of collector aspect ratio on the collector efficiency of baffled solar air heaters”, Energy, 23, 11-16. [12] Kumari, P., and Sharma, S.P., (2000) "Enhancement of thermal performance of solar air heater with extended surfaces absorber", XVI National Convection of Mechanical Engineers, Sept. 29-30, 2000 Roorkee, pp. 621-627. [13] Kumari, P., and Sharma, S.P., (2000) "An analytical investigation on thermal performance of finned absorber solar air heater", National Renewable Energy Conference 2000, Nov. 30-Dec.
19. 19. Cont. [14] Kumari, P., and Sharma, S.P., (2001) "Thermohydraulic performance of extended surfaces absorber solar air heaters", Third National Conference on Thermal Systems, Organised by Mechanical Engg. Deptt. I.T. B.H.U., Feb. 17-19. [15] Chand,P.and Sharma, S.P., (2010) ”Thermal performance prediction of extended absorber solar air heater” Proc. of the 20thNational and 9thInternational ISHMT-ASME Heat and Mass Transfer Conference, January 4-6, IIT Mumbai, India.