Thermal Performance Analysis And Experimental Study Of Parabolic Trough Collector

Solar energy, as one of the inexhaustible, clean and renewable energy, attracts moreand more attention by industry and science community. Solar power generation,including photovoltaic and solar thermal power generation, is an important way of solarenergy utilization. Photovoltaic power generation has been widely used, although thereare still limitations of efficiency and cost. Solar thermal power generation is promisingtechnology in the future due to its advantages in large-scale dispatchable electricitygeneration. According to the ways of heat collecting, there are three types of solarthermal generation system, namely parabolic trough, solar tower and dish-stirling.Among them, parabolic trough system is a quite mature technology, which has beenoperation commercially in US and some European countries.Parabolic trough collector is one of the main components of parabolic trough solarthermal power generation system, which is used to convert solar energy into heat. Theperformance of parabolic trough collector affected directly the efficiency and cost ofsolar thermal power plant. In such thermal collector, heat conduction, convection andradiation happen simultaneously and the heat transfer process has significantnon-uniform characteristics in space and time.In this paper, a heat transfer model is established by analyzing the working processof trough collectors. Then the thermal efficiency of the parabolic trough solar receiverand the outlet temperature of heat-transfer fluid are calculated under the conditions ofdifferent solar radiation intensity, fluid flow rates and inlet temperatures. Throughnonlinear fitting of the calculated data, an empirical correlation of collectors’ efficiencyand heat-transfer fluid outlet temperature is obtained.Considering the non-uniform surface heat flux of the parabolic trough receiver, anew heat transfer model of trough collector is established. Based on that, the variationof the collector performance with the relevant parameters is also analyzed. The resultsshow that the collector efficiency degrades with the increase of the wind speed andheat-transfer fluid inlet temperature. And collector efficiency improves with the increaseof solar radiation intensity, flow rate and ambient temperature. The wind speed andambient temperature have less impact on the collector performance. Solar irradiation,heat-transfer fluid inlet temperature and flow rate are the three main factors that affectthe collector performance. Steady state equilibrium tests of parabolic trough receiver are performed in the wayof electric heating simulation. The heat loss characteristics under different walltemperatures and vacuum conditions are obtained. Experimental results show that theheat loss of the tested receiver is917.5W at the wall temperature of about400℃. Whilethe receiver is heated and cooled many times, all the components of the receiver workwell and there is no crack in the seal between the glass envelope and metal heading. Thetest results also show that the high-temperature selective absorption coating has noobvious performance degradation.