Optimal Performance for Solar Thermal Power System

Transcription

1 Energy and Power Engineering, 2009, doi: /epe Published Online November 2009 ( Optimal Performance for Solar Thermal Power System Jianfeng LU 1, Jing DING 1, Jianping YANG 2 1 School of Engineering, Sun Yat-Sen University, Guangzhou, China 2 ey Laboratory of Enhanced Heat Transfer and Energy Conservation of the Ministry of Education, South China University of Technology, Guangzhou China liujf 01@mails.tsinghua.edu.cn Abstract: Solar thermal power is currently one of the important trends and research hotspots of solar energy. In present paper, basic physical model is proposed to investigate the solar thermal power, and the operating temperature is optimized to maximize the electricity generating efficiency. When the concentrated energy flux rises, the absorption efficiency of heat receiver will first increase and then decrease, while the increasing of flow velocity can improve the absorption performance. As the working temperature rising, the heat loss of infrared radiation and natural convection increases quickly, so the absorption efficiency obviously decreases, while the Carnot efficiency of the steam turbine cycle will rise. Because of the coupling effects of the heat absorption cycle and turbine cycle, the electricity generating efficiency will reach maximum with the optimal working temperature. eywords: solar energy, heat receiver, operating temperature, electricity generating efficiency [1] Carnot Fujiwara [2] Clausing [3] Dehghan Behnia [4] [5] Steinfeld Schubnell [6] Segal Epstein [7] 1 T f0 T fl /

2 J. F. LU ET AL. 111 T f0 T fl Figure 1. Solar thermal power system r R T(x,0) x L 2. Figure 2. The heat transfer process in the heat receiver [8-9] 2 R I =1- h n I I I h ( T T ) T q (1) 4 n w s w f T s q f f f w f q h T T (2) h f T f [10] k hf Nu (3) D Nu Re Pr (4)

3 112 J. F. LU ET AL. (2)(1) 4 n( w s) w f w f I h T T T h T T (5) R qf 2R cptur2rdr x 0 Tf R T cp ur2rdr c 0 p R x x u av (6) f 2 uav q h f f Tw Tf ab (7) I I L 1 ab L 0 abdx (8) T fl Carnot [11] Tfl Ts c (9) T fl (10) ab R=0.01m L =1m 5Wm c =1.77kgm -3 c p =1006Jkg -1-1 Pr=0.743 k=0.0181wm -1-1 = kgm -1 s -1 Co-Cd-BT [12] =0.96 = T f =473u av =5.0m/s 20kWm kWm % 4 T f =473I=10kWm -2 5 m/s 60% 15 m/s ab I (kwm -2 ) 3. Figure 3. The temperature distributions and absorption efficiency under different energy fluxes

4 J. F. LU ET AL ab u (m/s) 4. Figure 4. The temperature distributions and absorption efficiency under different velocities ab T f x (m) ab T f x (m) 5. Figure 5. The temperature distributions and absorption efficiency under different inlet temperatures T f0 = u av =10.0m/sI=10kWm % 44.4% u av =10.0m/s I=10kWm -2

5 114 J. F. LU ET AL c ab T fl () 6. Carnot Figure 6. The absorption and Carnot efficiencies under different working temperatures T () 7. Figure 7. The electricity generating efficiency under different working temperatures % 44.4% % 59.5% 7 u av =10.0m/sI=10kWm % 3-4 REFERENCES [1] S. A. alogirou, Solar thermal collectors and applications, Progress in Energy and Combustion Science, Vol. 30, pp , [2] M. Fujiwara, T. Sano,. Suzuki, et al., Thermal analysis and fundamental tests heat pipe receiver for solar dynamic space system, Journal of Solar Energy Engineering, Vol. 112, pp , 1990.

6 J. F. LU ET AL. 115 [3] A. Clausing, Analysis of convective losses from cavity solar central receivers, Solar Energy, Vol. 27, pp , [4] A. A. Dehghan and M. Behnia, Combined natural convection conduction and radiation heat transfer in a discretely heated open cavity, ASME Journal of Heat Transfer, Vol. 118, pp , [5] Z. G. Liu, C. P. Zhang, Y. H. Zhao, and D. W. Tang, The design and experiments of a new cavity absorber, Acta Energiae Solaris Sinica, Vol. 26, pp , (in Chinese) [6] A. Steinfeld and M. Schubnell, Optimum aperture size and operating temperature of a solar cavity-receiver, Solar Energy, Vol. 50, pp , [7] A. Segal and M. Epstein, Optimized working temperatures of a solar central receiver, Solar Energy, Vol. 75, pp , [8] C. E. ennedy, Review of mid- to high-temperature solar selective absorber materials, NREL/TP , [9] Y. Sun, Y. Y. Shi, and F. C. Wang, Study on thermal stability of solar selective absorbing surfaces with new material, Acta Energiae Solaris Sinica, Vol. 23, pp , (in Chinese) [10] J. H Lienhard IV and J. H. Lienhard V, A heat transfer textbook, Phlogiston Press, Chambridge, Massachusetts, U.S.A, 2002 [11] R. T. Stephen, Thermodynamics: concepts and applications, Cambridge University Press, New York, 2006 [12] L. Cindrella, The real utility ranges of the solar selective coatings, Solar Energy Materials and Solar Cells, Vol. 23, pp , 2007.