Design Of Non-imaging Solar Concentrator With No Light Escape In The Gap And Research On Its Photothermal Performanc

As a kind of renewable energy,solar energy has the characteristics of wide distribution,huge reserves and environmental friendliness.However,solar energy also has the disadvantages of low energy density and uneven regional distribution.Therefore,it is necessary to concentrate solar energy.In the process of collecting heat in traditional solar vacuum tube concentrator,there is a gap between the inner tube and the outer tube of circular absorber,which will lead to light escaping from the gap between the interlayer.Based on the CPC(Compound Parabolic Concentrator,CPC),used the principle of non-imaging optical edge light and geometrical optical reflection law,the ELE-CPC(Eliminate Light Escape-CPC,ELE-CPC)was designed,which can eliminate the escape of light in the interlayer gap of vacuum tube.The mathematical model of solar energy ELE-CPC of vacuum tube absorber is constructed.The correctness of the heat transfer model and the photothermal conversion performance of ELE-CPC were verified by an outdoor photothermal conversion experimental platform made by ourselves.The main research contents and conclusions are as follows:(1)Based on the geometric light reflection law,the mathematical model and numerical calculation method of circular absorber ELE-CPC are derived by using analytic geometry method.By Monte Carlo ray tracing method,it is verified that the solar rays reaching the surface of the equal-length reflector can be captured by the absorber after being reflected by the reflector.In addition,when the number of equal-length reflectors increases from one pair to six pairs,the length of a single equal-length reflector decreases from 23.50 mm to7.65 mm.Because of the wave-particle duality of light,the length of reflectors should not be too much in practical application.(2)Compared with the S-CPC(standrand CPC,S-CPC),the optical efficiency of the ELE-CPC is improved by about 15.7%,and the energy flux density distribution on t he absorber is improved.In addition,the annual radiation collection capacity of ELE-CPC is evaluated.The results show that the radiation received by ELE-CPC with single pair of equal-length reflectors in the four seasons are increased by 4.8%,4.9%,5.0%and 7.7%respectively compared with the S-CPC.Especially in winter,the energy increase is obvious.(3)According to the principle of energy conservation,the photothermal conversion model of ELE-CPC is constructed,and the theoretical numerical solutio n of the photothermal conversion model of ELE-CPC is obtained.Outdoor experiments show that the average output temperature of ELE-CPC system is 366.4 K,the average efficiency is61.3%,and the maximum relative error of theoretical model calculation value is less than13.2%,which effectively verifies the practicability of the model and the reliability of the experimental platform.(4)The ELE-CPC system has the characteristics of high-efficiency photothermal conversion and heat energy transmission.The av erage conversion utilization rate of the absorber to solar radiation is 89.5%,and the average heat loss is only 17.5 W.In addition,the outlet temperature of vacuum tube in ELE-CPC system decreases with the increase of working medium flow rate.When the flow rate of the working medium is 5m~3/h and 7m~3/h,the maximum outlet temperature of the vacuum tube can reach 374.1K and 354.9K,which can meet the requirements of the outlet temperature in different application scenarios.