| Flux density distribution of parabolic though collector tube,the optimization of reflector and thermal performance of collector were theory analyzed,simulated and experimental studied based on the climatic characteristics of the alpine region to solve the problem of flux density distribution by the mirror focusing of parabolic trough collector system,the heat loss of high temperature was large,and the efficiency was low.Aiming at the problem of the shield of collector tube,the complete type parabolic shape and non-intact type parabolic collector system was simulated,and the geometric parameters were optimized.The results showed that when the cutting width was less than the outer diameter of the glass tube,the cutting width had little effect on flux density distribution of metal tube surface.The maximum of flux density increased with the geometric concentration ratio increasing,the edge angle decreasing,the opening width increasing,the focal length increasing,the diameter of the metal tube decreasing.According to the orthogonal optimization design,the optimal structure parameters of system was: the opening width of 2.25 m,the focal length of 1 m,the metal pipe diameter of 0.04 m,the concentrator center cutting width of 0.25 m.Through the establishment of trough collector simulation model,influence factors of thermal efficiency and energy efficiency of collector was simulated and analyzed.And the heat transfer enhancement factor and enhancement coefficient was introducted to reflect the heat transfer efficiency of nanofluids heat transfer medium.The results showed that thermal efficiency and energy efficiency of the optimized trough collector was greater than the original equipment and complete parabolic concentrator system.Enhancement coefficient of heat transfer medium increased with the increase of mass fraction and the fluid inlet temperature.Particle size of 10 nm,20nm and 30 nm nanofluids heat transfer enhancement factor maximum were 1.110,1.109 and 1.103,the enhancement coefficient maximum were 1.220,1.217 and 1.214,respectively.Flux density measurement system of parabolic trough solar collector was built in this paper,and flux density distribution of collector tube was experimental studied by using target and CCD camera of indirect measurement method.Flux density distribution of collector tube was analyzed when the sun and clouds cover The results showed that flux density of collector tube surface increased with the increase of direct solar irradiance when the sun.The distribution of flux density along the tube diameter was the same,and two peaks appeared.The radiation was shielded by the bracket and the equipment connection which leaded to the flux value of the collector tube surface smaller,and with the decrease of the incident angle of the sun,the sheltered position gradually moved to the east side of the tube.Flux density of collector tube surface was decreased leaded by clouds.Parabolic trough collector system was built in this paper,the collector performance of system was studied by the experiment in the cold region.The thermal efficiency and energy efficiency of the original non-complete type concentrating collector system were analyzed.And instantaneous efficiency normalized temperature difference equations of parabolic trough collector was obtained.The results showed that the change trend of thermal efficiency and energy efficiency of parabolic trough collector was the same as direct solar irradiance.When the fluid inlet temperature was equal to the ambient temperature,under the condition of no heat loss,the instantaneous thermal efficiency of parabolic trough collector was 69.81%,the simulation value was 73.16%.The higher the fluid inlet temperature and the lower the ambient temperature,the greater the heat loss,thermal efficiency of the parabolic trough collector was smaller.This work provided the theoretical and experimental basis for further study of thermal performance of collector in the cold region. |
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