An Investigation On The Efficiency Of Hemisphere Cavity Receiver And Thermoelectric Generator

More attention are paied on solar thermal system because of the environmentalpollution and energy shortage,theoretical and experimental research are done on thehemisphere cavity receiver in solar thermal system.The main work is following.Firstly, the study on convection heat loss of receiver is done by Fluent, theinfluence on convection heat loss by angle of inclination of receiver is obtained, theresults shows:(1) stagnation region appears in the receiver, the boundary of region isthe horizontal plane through The top of the receiver apeture, the temperature gradientis high in the boundary.(2) Convection heat loss will decrease when the inclination ofreceiver increase, it decrease faster when inclination angle is between30°and60°than0°~30°and60°~90°, it is close to0on90°.(3) There is almost noinfluence on the flow and temperature of air in the receiver by conduction andradiation.Secondly, the optical analysis is obtained by TRACEPRO, a new model ispresented combined with heat transfer theory, The accuracy of the model with highoperating rate can meet the requirements of engineering. Outdoor experiments withdish solar collector are done to prove the new model. The heat transfer fluid is oil.Finally the investigations on some factors which have influence on the efficiency aredone by the model, the conclusion are follows:(1) The flow rate should be keepedhigher than the minimum to avoid the laminar flow when decrease inlet temperature,it is similar when decrease the flow rate.(2) The efficiency will decrease when theradiation intensity is too high, so the concentration ratio of solar thermal systemshould not be too high.(3) The influence on efficiency is very small when flow rate ishigh, and exergy of the oil decrease with the increase of flow rate, the efficiency andoutlet temperature both increase with the decrease of flow rate when radiation is lowand temperature is high.Again, a solar dish system using heat-transfer oil (Model SYLTHERM800) asheat transfer fluid is established, based on which, variable conditioning experimentsare carried out to investigate the influence of these parameters on the efficiency. Theexperimental system consists of a parabolic concentrator, a hemispherical cavity receiver and the cycling system. The adjustable parameters includes the heat transferfluid mass flow rate (variation range0.03-0.06kg/s) and the heat transfer fluidtemperature at the receiver inlet (variation range110-190℃), and the solar radiationintensity changes within a range of400-900W/m2during the tests. The experimentalresults indicate:(1) When the qualitative difference in temperature(the averagetemperature of the inlet and outlet over the ambient temperature) increases, the totalefficiency decrease, the change is in5%—7%in the experiment.(2) With the increaseof the mass flow rate increases from0.03kg/s to0.06kg/s, the total efficiencyincreases from45%to75%, and its rate of increase is getting larger in the experiment.(3) The larger the solar radiation intensity is, the higher the total efficiency gets.Finally, the experimental study is done based on the upper system combined withthermoelectric generator, the conclusion are follows:(1) The efficiency will stilldecrease when the inlet temperature increase, but it is lower, the generating voltagehas a linear growth when the inlet temperature increase.(2) The generating voltagewill not change when the beam radiation density increases.(3) The generating voltagewill not change when the mass flow rate of water decrease.