Field Optimization And Thermal Performance Analysis Of Linear Fresnel Concentrator Based On Seasonal Variation

This paper considers on the features of much wind and sand and high latitude in Hohhot,resulting in serious end loss and dust deposition on the mirror of linear Fresnel collector,and affecting the thermal efficiency of the system.In this paper,a linear Fresnel concentrator experimental system is established.Based on seasonal variation and simulating,analyzing the change of end loss of the receiver are combined.The end loss compensation method is searched,and the decreasing of light collection or thermal efficiency caused by dust deposition is studied.By analyzing the principle of linear Fresnel concentrating light,the maximum lighting half angle and the filling rate of the mirror field are introduced to optimize the structure of the mirror field,and the optical efficiency of the system analyzed.The result shows that when the solar incidence angle is 30 ° and the filling ratio of mirror field is 0.5 and 0.6 respectively,the optical efficiency of the system is the lowest,and the system efficiency increases with the maximum half-angle of lighting decreases.A linear Fresnel system with north-west tracking is established.Based on the seasonal changes in the Hohhot area,the instantaneous thermal efficiency of the linear Fresnel concentrator system is tested and cosine loss of the system caused by seasonal changes is analyzed.The result shows that the ambient temperature is high in June,and the theoretical thermal efficiency is 52%.In December,with the decreasing of the ambient temperature,theoretical thermal efficiency of the system is reduced to 33%.In summer,the cosine loss of the system is less than 5%,and the average cosine loss in spring and autumn is 14%;the average winter cosine loss is 40%.And the decreasing of optical efficiency of the system caused by cosine loss in winter leads to a significant decrease for thermal efficiency of the system.Considering end loss of the linear Fresnel receiver caused by seasonal changes,and this paper analyzes the end-loss in different seasons and proposes an end-loss compensation method to measure the instantaneous thermal efficiency of the system before and after end-loss compensation.The result shows that the end loss of the receiver is maximum at noon and the end of the receiver was minimal in the morning and evening.In the same period of time,the end loss of the receiver is the highest in winter and the lowest in summer,and the same in spring and autumn.After compensating,the end loss of the receiver is minimal at noon,and the end loss of the receiver is the greatest at the end of morning and evening.The thermal efficiency of the system is increased by 40% at noon.Analyzing the influence of the dust accumulation density and the shape of the mirror element on the thermal efficiency of the system which is caused by the dust accumulation period time and the seasonal variation.The results shows that thethermal efficiency of the system is reduced by 14.8%,31.5% and 44.18% respectively,in the case of two days,four days and ten days of dust accumulation without rainfall.The reflectivity of the mirror element decreases with the increase of dust accumulation period time.The influence of rainfall on the dust accumulation density is great.With more rainfall weather,the instantaneous thermal efficiency of the system fluctuated around 40%,which is 12% different from that of the mirror cleaning system.The instantaneous thermal efficiency of the system shows a decreasing trend.The average dust accumulation density of the primary mirror field decreased due to the rainfall,and the change of dust deposition morphology has a significant influence on the thermal efficiency of the system.