Flow And Heat Transfer Performance Study Of Liquid Immersion Cooling System For Linear CPV

Concentration photovoltaic (CPV) systems have high sunlight to electricityefficient, and has been considered as an effective way to reduce the cost ofphotovoltaic systems, so more and more attention has been paid to CPV technology inrecent years. However, effectively cooling of CPV solar cells is one important issuewhen designing CPV systems. Aiming at eliminating the shortages of conventionalCPV cooling method, a direct liquid-immersion cooling method was proposed forlinear CPV systems. In the present thesis, experimental and numerical simlationworks on performance study of liquid-immersion cooling for linear CPV systemswere carried out as follows.1. Effect of silicon oil thickness on solar cell electricity performance wasinvestigated experimentally. The results show that the electrical characteristics of bothconcentrator silicon solar cells and concentrating triple-junction (CTJ) GaAs solarcells are improved compared with solar cells without liquid immersion. However, theelectrical characteristics of both concentrator silicon solar cells and CTJ GaAs solarcells are decreased with increasing silicon oil thickness when immersed by liquid.This indicates that the thickness of immersion liquid on front surface of solar cellshould be as thin as possible.2. A linear flat mirror concentrator system was designed, and according to resultsdeduced from the geometric relation, it can be seen that the minimum distancebetween two adjacent mirrors without shadow increases with mirror location angleand sunlight incident angle. When the mirror location angle and sunlight incidentangle is equal to45o, the minimum distance between two adjacent mirrors is equal to1.414times of mirror width. According experimental test result, the concentrationratio of the concentrator prototype is12.90X.3. A narrow rectangular channel receiver was designed and its performance wasinvestigated experimentally. The results show that the cell temperature can becontrolled in the range of20-31°C at a DNI of920W/m2, silicon oil inlet temperatureof15°C and Reynolds numbers of receiver solar cell region variation from8359to1671, and the correspondging convective heat transfer coefficient was280-1000W/(m2K). Electrical performance of the cells immersed in the silicon oil is stable andno obvious efficiency degradation was observed after immersed for270days. 4. Computational fluid dynamics models of narrow rectangular channel receiverswere established and the simulation results show that the optimum installationposition of solar cells is in the middle along the channel height direction. The lengthof the channel inlet and outlet region has minor effect on cell temperature. Smallerchannel makes for better heat transfer performance, however, receivers with lowerchannel heigth means larger flow resistance. The channel height is optimized as10mm. By regression analysis, general correlations of convective heat transfercoefficient and friciton coefficient were obtained.5.Liquid-liquid direct contact and phase change heat transfer experiment ofdimethyl silicon oil-methanol system was designed for cooing of immersion liquid.Experimental results show that lift tube temperature on axial direction is increasedfirstly and then tends to be stable. The volumemetric heat transfer coefficient canreach22-34kW/(m3K); The range of average gas holdup of lift tube is0.05-0.5, andunder this average gas holdup range, the dimethyl silicon oil Reynolds numbers ofreceiver solar cell region in the optimized rectangular channel receiver can reach1500-7500when only using methanol steam lift as driving force.