Study On The Optical And Thermal Performance Of Fixed-focus Linear Fresnel Lens Solar System With Sliding Adjustment

Based on the technical dilemma that the existing reflective line focusing technology can not be extended to civil houses on a large scale,a Fixed-Focus linear Fresnel lens solar system with sliding adjustment（FLFS）is developed in this thesis.The system adopts the Fresnel lens for focusing components,through a series of design,the overall system of portable,compact,It can effectively overcome optical loss such as end loss and cosine effect,and is suitable for roof of ordinary civil house/workshop.In this thesis,the construction idea and design principle of the system are described in detail.Then,the optical model is simulated based on Monte Carlo ray tracing method.Based on the results of optical simulation,the Fixed-Focus linear Fresnel lens solar system and the related test system were built,and the heat collection efficiency of the system was investigated by selecting several sunny days.The influences of direct solar radiation intensity,whether the cavity surface is coated with black paint,whether the cavity surface is covered with transparent cover,and the inlet flow rate of working medium on outlet temperature and heat collection efficiency are gradually explored.The ratio of photothermal loss in each experimental case is analyzed,and the main conclusions are as follows:With the increase of the solar declination angle,the focal line of the linear Fresnel lens moves in both the north-south and vertical directions.When the solar declination angle increases to 23.5°,the focal line of the linear Fresnel lens with the focal length of 650 mm rises98.7mm vertical y and moves 243 mm horizontally.The sliding adjustment designed in this thesis can reduce the optical loss of the system by about 10% per year on average.The relative optical efficiency of the system is significantly affected by the internal surface absorption rate,solar declination angle and solar hour angle.The higher the internal surface absorption rate,the higher the relative optical efficiency.The larger the solar declination angle,the lower the relative optical efficiency,and the larger the solar hour angle,the lower the relative optical efficiency.The optical efficiency of the system is significantly affected by the cavity distance.The optical efficiency of the system decreases with the increase of the lens-cavity distance.When the inner surface absorption rate is 0.85 and the cavity distance is 600 mm,625mm,650 mm,675mm and 700 mm,The average optical efficiency of plate triangular cavity in one year is 81.14%,79.17%,74.97%,69.73% and 62.77%,respectively.The average optical efficiency of the triangle cavity is 75.98%,71.74%,66.50%,60.39% and 54.03%,respectively.The optical efficiency of the triangular cavity constructed by plate is general y higher than that constructed by tube.Direct solar radiation intensity has little effect on the heat collection efficiency,but has a significant effect on the outlet temperature of the cavity,and has a positive correlation.When the surface of the copper tube in the system cavity is coated with black paint and no cover plate,the outlet temperature is 49.6℃ and the heat collection efficiency is 30.4% when the direct radiation intensity is 400 W.When the direct radiation intensity increases to 500 W,the outlet temperature is 53.4℃ and the heat collection efficiency is 29.91%.Black paint has a great influence on the heat collection efficiency.Under the same other conditions,the heat collection efficiency of copper cavity coated with black paint is general y improved.Adding transparent cover plate can improve the heat collection efficiency of smooth copper tube cavity,but will reduce the heat collection efficiency of black copper tube.The flow rate will affect the outlet temperature and heat collection efficiency.For the system with direct solar radiation intensity of 500 W,no transparent cover plate and black painted copper tube cavity,when the flow rate increases from 0.0012kg/s to 0.002kg/s,the average outlet temperature drops from about 55℃ to about 45℃.The heat collection efficiency increased from 30.93% to 32.25%.In this thesis,from the perspective of optical simulation and experiment,the influence of photothermal characteristics and parameters on the Fixed-Focus linear Fresnel lens solar system with sliding adjustment is systematical y studied,which provides a new idea and data support for the design and optimization of the new solar concentrator system.