Numerical Study On The Light Concentrating Characteristics And Thermal Performance Of CPC Microchannel Solar Collector

The solar rays reflected by the CPC would form nonuniform heat flux distribution on the circumferential direction of the surface of the heat absorber.When the CPC concentration ratio was large,the surface of the heat absorber would generate light spots with high heat intensity.As a result,the temperature distribution difference of the heat absorber was large,which would cause serious consequences such as thermal stress deformation and damage of the absorption coating.Therefore,how to uniformize the heat flux distribution on the surface of the heat absorber and how to make the temperature distribution of the heat absorber more uniform had become a research hotspot of concentrating solar collector.Based on this,a new type of CPC microchannel solar collector was proposed and designed.The scale effect of the microchannel heat absorber could equalize the temperature distribution of the heat absorber.The heat transfer process of collector was analyzed theoretically by heat balance method.The model of plate CPC microchannel solar collector was established.Research were carried out on the light concentration characteristics of CPC microchannel solar collector at different light incidence angles,CPC concentration ratio and truncation ratio.On this basis,the numerical calculation model of the microchannel heat absorber was established to study the temperature distribution rule of the heat absorber under the nonuniform heat flux distribution.The numerical calculation model of the collector was established to study the influence of ambient temperature,inlet water temperature,water flow velocity and the length of the heat sink on the collector performance of the collector.The main contents and conclusions were as follows:?1?The simulation study on the light collecting characteristics of CPC microchannel solar collector with vertical panel showed that the heat flux distribution on the left and right sides of the vertical heat absorber was quite different at different incident angles.The peaks of heat flux on both sides were complementary to each other.When the light incident angle was at less than half angle,the average heat flux on the surface of the heat absorber did not change more than 3.8%.The average heat flux on the surface of the heat absorber was not more than 3.5%.To reduce contact heat transfer,it was recommended to truncate the bottom of CPC.?2?The simulation study on the light collecting characteristics of CPC microchannel solar collector with horizontal panel showed that when the ray incident angle is 0°,the heat flux on the surface of the heat absorber presents a complementary distribution about the axis of the central point of the heat absorber.When the light was incident at a nearly received half angle,the peak value of heat flux on the surface of the heat absorber was the largest,which is 250%of the incident value of 0°.The truncation ratio was set to 0.5 could improve the economy of the system while having less impact on CPC concentrator.?3?The thermal performance of microchannel heat absorber was simulated and the results showed that due to the scale effect of the microchannel,the tube wall homogenized the heat distribution,so that the temperature of the outlet cross section of the heat absorber was uniformly distributed under different incident angles of light,concentration ratio and truncation ratio.And the nonuniform index did not exceed2.15?10^-3,reflecting the advantages of microchannel heat exchangers with strong thermal conductivity.?4?The heat collecting performance and heat loss of the collector unit were simulated and the results showed that when the ambient temperature increased from279K to 308K,the heat collecting efficiency of the whole machine increases by 16%,which indicated the increase of surface ambient temperature could enhance the heat collecting efficiency of the whole machine.The maximum heat collection efficiency under different inlet water temperature was 97%.As the inlet water temperature increased,the heat collection efficiency decreased.The velocity of heat transfer medium and the length of heat sink had little effect on the heat collecting efficiency.The heat loss of the whole machine was mainly caused by heat leakage from the glass cover and the insulation bottom layer,of which the heat leakage from the glass cover was twice as much as that from the insulation bottom layer.