| In order to solve the contradiction between output power and working efficiency of Fresnel lens,the orientated light transmitting Fresnel lens solar concentrator(LTF-SC)has been designed,and the medium-high temperature solar collector system composed of the Fresnel concentrators and center receiver(SCS-FCCR),whose the concentrator field module is LTF-SC,was proposed.Due to the use of fixed orientation light-transmitting technology and modular design idea,LTF-SCs in SCS-FCCR can transmit concentrated sunlight to a fixed direction independently.Through the research method of theoretical derivation,numerical simulation and experimental verification,an experimental platform of LTF-SC was established to test thermal performance and its optical model was built to validate by ray tracing.The main research contents and results were summarized as follows:(1)Full explanation of how the LTF-SC and SCS-FCCR works and design was presented.The practice experiment of thermal performance of LTF-SC has been completed.The results show that collector efficiency of LTF-SC under steady state decrease first,and then increase over time,while the minimum value was found at true solar time 12:00.Average temperature difference between inlet and outlet and collector efficiency of coil collector are 0.754℃ and 32.72%respectively.(2)According to the proposed design method and parameters,the optical model of LTFSC has been completed in the SolidWorks,then been simulated in the TracePro.The simulation results indicative that when collector’s thermal loss coefficient is 0.65,the simulation results agree well with experimental results,which prove that the optical model is reliable.(3)The sun was tracked so as to obtain the daily and yearly change rule of the optical efficiency of LTF-SC,which locate at north and south sides of center receiver in SCS-FCCR.The simulation results show that the optical efficiency of LTF-SC on south side decrease first,and then increase throughout the day,while the minimum value were found at true solar time 12:00,but it appears the opposite rule on the summer solstice.The optical efficiency of LTFSC on north side has no clear change in a day.During the year,the average optical efficiency of LTF-SC both on north and south sides is 53.04%and 52.00%respectively.There is a direct correlation between the daily and yearly change rule of the optical efficiency of LTF-SC and the loss of light,and suggested reasons for its includes dimensionless variables κi and κ2,which indicate the reflected light in concentrated sunlight percentage and the collimating light in reflected light percentage.(4)By studying influencing mechanism of pitch angle tracking error,rotation angle tracking error and installation error in the optical efficiency of LTF-SC,conclusion is drawn:the error of pitching motor and rotating motor should be controlled within±0.1° and±0.5°separately,and both are not allowed more than±0.1°.The deviation value of the focus of Fresnel lens from the focus of parabolic reflector of the orientated deflector is not recommended for more than 0.1.(5)Using orthogonal experimental design,the main structural parameters affecting the thermal efficiency of annual average optical efficiency of LTF-SC are analyzed and researched.The result shows that the main structural parameters decreasing order which affects annual average optical efficiency of LTF-SC on north side significantly are light transmission distance L,geometric concentration ratio C,semi-focal chord p,interaction between p and L,which on south side are light transmission distance L,geometric concentration ratio C,interaction between p and L,semi-focal chord p,the reflectivity of parabolic reflector of the orientated deflector,the absorptivity of collector receiving surface.When the main structural parameters all choose the best condition,annual average optical efficiency of LTF-SC on north and south sides is 81.31%and 62.26%respectively. |
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