Thereotical And Experimental Investigation Of Linear Concentrating Solar Collector With Cavity Absorber

Linear concentrating solar collector is a main technique in the area of middle and high temperat. solar thermal utilization. When the heat source temperat. range is between 100?C and 300?C, linear solar collector can keep high thermal efficiency and advantage of cost. At present, the most popular absorbed used in linear solar collector is the metal-glass evacuated tube. Although the evacuated layer between metal tube and glass annular largely reduces the heat loss, it is inevitable that there is vacuum leakage after long time working. But the reliability can be increased effectively and research and producing cost will also be down if the cavity absorbed is chosen. So this thesis is devoted to research on the middle-high temperat. parabolic trough/Fresnel lens solar collector with cavity absorber and its application. The main works are summarized as following:(1)Three dimensions concentrating mathematical models for linear flat Fresnel lens and trough reflector which cutting surface is conic curve are developed. The influences of incidence angle, focus error, tracking error and surface error on concentration ratio and energy distribution in the concentrated light trap have been investigated. Based on the theoretical analysis results, one kind of parabolic trough reflector and one kind of flat plate Fresnel lens are designed and made. Moreover, experimental investigation of concentrating performance and accept angle have been done. The experimental results show that good optical efficiency can be gotten when the apert. width of absorber is 5cm and the accept angle is controlled between -0.4°and +0.4°(2)Four shapes of cavity absorbed which are semi-circular, arc, triangle and square shape are designed and made. Their optical and thermal performances are investigated under both experiment and theory. According to the results, the triangle shape cavity absorbed has better optical performance and the minimum heat loss. Furthermore, triangle cavity and squared cavity with two reflectors are chose and their construction is optimized. The conclusion is that the optimized depth of the former is 4cm and that of the later is 2cm. Based on these results, two kinds of 1m length cavity absorbed is produced.(3)The 0.64m2 flat plate Fresnel lens solar collector and 8m2 parabolic trough solar collector are designed and manufact.d. The developed micro controller for one-axis automatic sun-tracking can track the sunlight accurately. In four kinds of designed linear concentrating solar collectors, the parabolic trough solar collector with triangle cavity absorber appears the best performance. In fine day, the highest temperat. can reach 366°C. According to the thermal efficiency curve, the thermal efficiency of this solar collector is 46% when the flow media temperat. is 150°C and beam solar radiation is 600 W/m2. Moreover, heat transfer model is developed and the effect of struct. and material on thermal performance is analysis. The results show that the performance parabolic trough solar collector with cavity absorber is near that of parabolic trough solar collector with evacuated tube if the concentrator apert. is larger than 2m, the heat conductivity of insulation material is smaller than 0.0035 W/mK and the emissity of selective coating is smaller than 0.1.(4)The geometric models of the arrangement of non-tracking, one-axis tracking and two-axis tracking solar collector array have been developed. These models are useful for guiding how to arrange collector array in engineering practice. At the same time, the optimum distance of the array of three kinds collectors are calculated and fitted in equations, which can be used for reference.(5)Two kinds of systems in which linear concentrating solar collector can be used is supposed. One is the combined geothermal and solar power generation system, the other is combined CCHP system based on helical screw expander. Possibility analysis in Tibet is investigated. For the former system, the assisted heating of solar energy can enhance the power generation 38.6% (maximum). For the later one, both the yearly energy efficiency (40.2%) and exergy efficiency (13.1%) are higher than those of normal solar power generation system in which parabolic trough collector is used.