| As an effective way of solar energy utilization,one of the key advantages of concentrating solar power is to solve the discontinuity of power output through large-capacity heat storage technology and realize 24-hour continuous power generation.Linear Fresnel reflectors(LFRs)have a series of advantages of simple construction,low wind loads,low cost and optimal utilization of land area,and is gradually applied in large-scale power plants.In particular,the receiver of a composite parabolic secondary concentrator(CPC)+ vacuum collector can solve the technical problem of the high-temperature dynamic seal of the rotary joint,run a higher temperature heat transfer medium,and make LFRs have more potential in improving power generation efficiency and reducing cost.But at present,there are some problems,such as low optical efficiency,no standard method for optical design,and test.Based on the above analyses,the study object of this thesis is the LFR with the CPC.The research target is to improve optical efficiency.The research contents include analysis of optical performance index,optimization design of the CPC and mirror field,and simulation and performance test of the LFR system.Firstly,after the solar position algorithm,the main optical performance indexes and system efficiency calculation methods related to the design of the mirror field are analyzed in detail,and the performance analysis software of the LFR is compiled.The calculation method of shading and blocking efficiency of the mirror field based on the ray-tracing method is emphatically analyzed,and the results indicate that it has a small amount of computation and high efficiency,and can accurately calculate the shading and blocking efficiency of the mirror field.The method of calculating the concentrator ratio of the LFR with the CPC is discussed.Secondly,taking the CPC for the LFR as an object,the simulation model of the CPC geometric optical efficiency based on Matlab software is established,and the correctness of the model is verified by TracePro software.Based on this model,the effects of the choice of the gap,half-acceptance angle,and truncation ratio on the optical efficiency of the CPC are studied by using the ray-tracing method according to the characteristics of the LFR.The effects of the outer diameter tolerance,position deviation of the absorber tube,and the profile error on the geometrical optics efficiency of the CPC are analyzed.The concentrating characteristic of CPC is studied.The CPC,with 50° half-acceptance and 0.4 truncation ratio,could achieve the average geometric optical efficiency 84.52%.If the incident spot width is adjusted for a specific incident angle,the average geometric optical efficiency of CPC can reach 99.5%.Thirdly,the design method of the mirror field with varying width and equal width of the main reflector is studied.Aiming at the without shading mirror field within the specific incident angle range,the concentrating characteristics of the cylindrical main reflector are analyzed,and the relationship among the receiver height,the mirror field range,and the distance between the main reflectors is deduced.For the without shading mirror field,the CPC with 50° half-acceptance and 0.4 truncation ratio,and 21 cylindrical main mirrors with 500 mm width is used.When the initial angle of without shading is greater than 40 °,the system works in the range of incidence angle without shading but has blocking effect,which is very small and can be ignored;when it is beyond the range of without shading incidence angle,the shading and blocking efficiency decrease rapidly.With the increase of the initial angle without shading,the ground coverage of the center and the mirror field of the same main mirror increases gradually,while the average shading and blocking efficiency decreases gradually.Fourthly,based on the principle of geometric optics,calculation formulas of parameters that are needed for establishing the LFR model in SolTrace software were derived by geometrical optical principles,and a modeling method was given by the example,which demonstrates the correctness of our proposed designing method.The distribution of energy flow density on the surface of the absorber tube is analyzed.For the without shading mirror field of LFR,according to the two upper and lower regions of the surface of the absorber tube,the surface energy flow accounts for 44.31% and 55.69% respectively.The surface of the endothermic tube was divided into four regions,and the surface energy flows accounted for 18.67%,25.12%,27.90%,and 28.30% respectively.Lastly,based on the research results of this thesis,the design scheme of the LFR demonstration project is proposed.The measurement methods of the geometrical optical efficiency of the CPC and the mirror field are studied.The results show that the geometric optical efficiency of CPC based on Matlab calculation and test is very close,the maximum deviation between the two is 4.92%,the average deviation is 3.18%.The geometric optical efficiency of the condenser field is 100%,that is,all the reflected rays can enter the CPC opening.Under the test conditions,the maximum photo-thermal efficiency of the system is 58.77%,and the average photo-thermal efficiency is 38.92%. |
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