Optimization Research Of The Secondary Reflection Receiver For Linear Fresnel Condenser System

Energy,as an important pillar for the development of modern society,provides an irreplaceable driving force for economic prosperity and social progress.However,with the excessive use of fossil fuels,problems such as environmental pollution and ecological destruction have become increasingly prominent.Finding a balance between economic development and environmental protection is the current reality challenge facing humanity.In order to achieve sustainable development,energy transition is imperative.Solar energy,as a clean and sustainable energy source,has become an important choice for countries around the world in their energy transition paths due to its abundant reserves,green and environmental benefits.Concentrating Solar Power(CSP)technology,as one of the solar power generation technologies,has attracted a great deal of attention from scholars and related enterprises due to its stable power output and strong adjustability.Among the existing CSP technologies,Linear Fresnel Reflector(LFR)concentrating power generation technology has gradually become a hot technology in the field of concentrating solar power generation due to its advantages of simple structure,strong wind resistance,and low installation cost.As a key component of the LFR system that receives solar radiation and realizes optical-thermal conversion,the performance of the secondary reflector directly affects the overall efficiency of the system.This paper focuses on the secondary reflector and conducts research and optimization on the problems of uneven energy flow distribution on the surface of the collector tube and gap losses between the secondary reflector and the collector tube.Firstly,the LFR system model is introduced,and the concentrating principle and mathematical model of the Compound Parabolic Concentrator(CPC)as the secondary reflector are analyzed.Based on the Monte Carlo ray tracing method,the initialization of photons in the LFR system,the reflection and absorption of photons between the system components are introduced,and the shadow and occlusion effects of the LFR system are analyzed.A shadow-free layout of the concentrator field is proposed.The optical model of the system is established using Tonatiuh,and the optical path process of the concentrator field and CPC under different incidence angles is tracked and analyzed.The Local Concentrate Ratio(LCR)under this condition is compared with the model established in Matlab to verify the correctness of the optical model.Secondly,regarding the uneven distribution of energy flow on the surface of the heat-collecting tube in the secondary reflection receiver,this paper constructed a model of the linear Fresnel reflector system based on Tonatiuh optical simulation software.The relationship between the focal length of the cylindrical reflector and the position of the aiming point and the width of the light spot was studied.On this basis,the optical performance and uniformity of energy flow distribution of the linear Fresnel reflector system under different aiming strategies were investigated.The results show that using an aiming strategy with aiming points uniformly distributed within a certain range,the concentration system can maintain high optical efficiency while improving the uniformity of energy flow distribution on the surface of the heat-collecting tube.By adopting the optimized aiming strategy,the optical efficiency of the linear Fresnel reflector system can reach 87.4%,and the standard deviation of energy flow density on the surface of the heat-collecting tube is reduced from45.3% to 30.7%,and the energy flow density at the top of the heat-collecting tube is increased by 10.2%.Finally,to address the issue of gap losses in the secondary reflector,this thesis proposes a small-gap cavity receiver.Through comparison with other different configuration receivers for optical performance,it is found that this type of receiver can effectively reduce gap losses,and the concentration ratio and optical efficiency are increased by 6.4% and 6.6%,respectively,compared with traditional vacuum tube type receivers.Meanwhile,this paper establishes thermal models for both the vacuum tube type receiver and the small-gap cavity receiver,analyzes the energy transfer in each part of the receiver based on the principle of energy conservation,and uses COMSOL Multiphysics simulation software to simulate the established models.The temperature distribution inside the two types of receivers is analyzed,and the thermal radiation losses of the two types of receivers are compared.The research shows that under the constant temperature condition of 500 degrees for the metal heat collection tube,the thermal radiation losses of the small-gap cavity receiver are reduced by4.5% compared with those of the vacuum tube type receiver.This result can provide theoretical support for the optimization design of linear Fresnel concentrator systems.