Performance Analysis And Experimental Research On The Parabolic Trough Solar Collectors

Solar energy could satisfy the need of today’s environment and social development as a renewable energy.The parabolic trough collector has been widely used in the solar energy filed because of its high commercial value and wide range of application,but the optical and thermal losses generated during the operation process will produce some restrictions on its promotion and application.This paper takes the optical characteristics of the parabolic trough collector as the breakthrough point to analyze the heat flux distribution of the heat pipe by using the theoretical and experimental method.The main works includes the following aspects:First of all,based on the motion law of the sun,this paper explored the related calculation of the sun angle and the calculation model of solar constants,and deduced the formula of solar radiation on inclined surface and sunshine time.This paper analyzed the optimal angle of the collector and the optimum method for calculating the azimuth angle throughout all the year round.Secondly,this paper analyzed the optimal relative spacing of the collector array.By solar collectors in Yanshan as an example,the result showed when the width of parabolic mirror was 2.55m,the relative spacing should be between 2 and 3.According to the sun angle calculation model and the parabolic trough collector tracking model,the parabolic trough collector optical computing software was written in VB language,which was used to calculate the relevant angle,incident angle,cosine loss,end loss rate and other optical loss of the parabolic trough collector parameters of different latitude regions at any time throughout the year.The geometrical deduction and numerical calculation of the optical concentration ratio of the outer tube wall of the heat pipe was made and the defocusing phenomenon was analyzed quantitatively by using Matlab software.The influence of the collector’s parameters and on the average end loss coefficient of the endothermic tube was investigated.The influence of the geometrical concentration ratio and the edge angle on the optical condenser ratio Cr of the outer tube wall of the absorber tube was discussed under nonideal conditions,and it showed the sun cone angle had the effect of cutting and filling the heat flux density distribution of the outer wall of the heat pipe.The simulation showed that the thermal efficiency of heat tube could be promoted by properly increasing the inlet heat transfer temperature.Finally,the experimental platform of parabolic trough solar collector system was developed for testing the affecting factors of the collector thermal performance,including the instantaneous thermal efficiency of the collector,the energy loss during the nighttime of the system,and the heat loss of the volumetric heat exchanger.The experimental results showed that during the bright sunny weather the instantaneous efficiency was changed between 0.35 and 0.65,and the heat loss coefficient of heat exchanger was under1 W/(m~2·℃).The inlet oil temperature had a larger influence on the collection efficiency while the direct solar radiation values had less impact on the instantaneous thermal efficiency.Under the dusty operating condition,the collector instantaneous thermal efficiency was concentrated between 0.2 and 0.3,which reduced by nearly 45%as compared to clean condition.