Optimization And Study Of Mirror Field For Linear Fresnel Concentrating System

Today,the global demand for clean energy is increasing every year.As a kind of renewable energy,solar energy has become the focus of research by scholars and experts because of its clean,non-polluting,abundant reserves and other advantages.Solar radiation is widely distributed in China and even the world,and solar energy can be fully utilized for energy generation.Solar power is divided into photovoltaic generation and solar thermal generation.At present,photovoltaic generation industry upgrade development is more mature,while photovoltaic generation technology started late,and relatively backward compared to solar thermal generation technology.The bottleneck of commercial application is high power generation cost and poor system stability.Solar power is divided into Parabolic Trough Collector,Parabolic Dish Collector,Solar Tower Collector and Linear Fresnel Reflector(LFR)according to the difference of concentrated form.Among them,LFR has attracted the interest of researchers because of its advantages of high land use,low wind load and simple structure.As the energy input device of the whole system in the LFR,the key to improve the optical efficiency of the system is to analyze and study its focusing performance.Hence,optimization and study of photothermal performance of the research system is of great significance for improving the efficiency of the LFR.First,the principle and algorithm flow of Monte Carlo ray-tracing are analyzed,and the optical model of the system is established based on the Monte Carlo ray-tracing method.The flow is divided into five modules: creation of the mirror field coordinate,the initialization of photons,the tracking of the primary mirror,the shadow and block effect,the reflection of photons on the mirror and the absorption on the absorber.Then based on the design principle and structural formula of Compound Parabolic Concentrator(CPC),a mathematical model of parabolic CPC and circular CPC are established in Matlab,and the design principle and concentrating principle of are analyzed.Based on the design parameters of the mirror field,Soltrace presents the optical process in the system.In Matlab,the light process in the mirror field is simulated at four angles of 45°,60°,75°,and 90°.Based on the design parameters in Matlab and Soltrace respectively,the distribution of the Local Concentration Ratio(LCR)in the absorber is simulated to verify the accuracy of the model.Secondly,the optical process of the incident light at the four incident angles of 45°,60°,75°,and 90° in the two CPCs is analyzed based on the optical model and geometric model,and the relationship between concentration rate and maximum acceptance half-angle,opening width and maximum acceptance half-angle in Matlab.It is analyzed the parameters that cause the optical loss and then propose an optimization method to reduce the loss.The effects of the intercept ratio,incident angle and acceptance half-angle on the optical performance of the two CPCs are compared and analyzed.It can be obtained that when the intercept ratio is 0.3,the concentration rate and optical efficiency of the two CPCs both reach the maximum.The change trend of the concentration ratio of the two CPCs is roughly the same at the same incident angle,and the LCR trends of the two CPCs show different changes with the angle of incidence.When the acceptance half-angle is 45°,the flux distribution of circular CPC is more uniform and the concentration is higher;when the acceptance half-angle is 50°,the flux distribution of parabolic CPC is more uniform and the concentration is higher.Finally,the analysis and prediction of the characteristics of the flux distribution on the surface of the absorber,the two-dimensional and three-dimensional flux density distribution diagrams are presented in Soltrace,the study analyzed the causes of uneven flux density distribution,introduced the principle and algorithm flow of particle swarm algorithm,and proposed a multi-objective optimization method of aiming lines based on particle swarm algorithm to improve the flux distribution in the upper half of the absorber by dispersing the aiming lines at the center of each column of the CPC main mirror field in the opening plane of the CPC.The optimization results show that the radiation originally located in the lower half of the absorber is dispersed to the upper half of the absorber by the dispersion aiming line,resulting in a flux distribution of 38.8% in the upper half of the absorber,and the circumferential radiation flux of the entire absorber is also relatively uniform.In this way,local overheating of the absorber wall is avoided,the local concentration ratio is improved,and the optical efficiency is improved.