Influence Of Heat Absorber Material And Porosity On Thermal Performance Of Solar Cavity Heat Absorber

Cavity heat absorber is an important component installed at the focal point of condenser and converts solar energy into heat energy.Its photo-thermal effect has an important impact on the performance of solar energy heat utilization system.The overall structure of heat absorber,the characteristics of heat exchange materials and the porosity of heat absorber are important factors that affect the energy-heat conversion process and conversion efficiency of heat absorber.Therefore,it is of great significance to compare and study the heat transfer characteristics of different endothermic materials and different porosity parameters.In this paper,volumetric solar heat absorber is taken as the research object,different heat absorber materials are selected and the energy-heat conversion characteristics under different structural parameters are studied.The work done can provide theoretical reference for improving the efficiency of solar photo-thermal utilization system.The specific research contents of this paper are as follows:Firstly,the research status of solar heat absorber at home and abroad is analyzed,the research methods of heat transfer characteristics of porous media at home and abroad are discussed,the theoretical analysis of internal flow and heat transfer characteristics of porous media is carried out,the radiation-convection coupling heat transfer calculation equation,internal flow control equation of porous media and physical model of cylindrical hole cluster cavity heat absorber are established for the structure of volumetric solar heat absorber,the grid system model is built based on Solid Works,and the photo-thermal conversion process of heat absorber is discussed.Secondly,based on the assumption of non-local heat balance and heat transfer in the Fluent software platform,the numerical calculation of the temperature distribution of the heat absorber is carried out,and the influence of five porous media heat absorbing materials such as alumina and zirconium dioxide on the energy flow conversion efficiency of the inner wall of the heat absorber is discussed.The results show that the energy flow conversion efficiency of silicon carbide porous media materials is up to 58.3%,and the rest are alumina,nickel alloy,copper oxide and zirconium dioxide,which are 36.6%,29.6%,16.3% and 4.6% respectively.Then,the energy flow conversion efficiency of alumina,copper oxide,nickel alloy,silicon carbide,zirconium oxide and other five porous media heat absorbing materials under different porosities was studied.The results show that under the same porosity,the energy flow conversion efficiency of the above materials will not change from high to low.Under different porosity conditions,the higher the porosity,the higher the energy flow conversion efficiency of the absorber.Finally,a photo-thermal conversion test bench for the dish-shaped solar heat absorber is established,and the focal plane energy flow input power of the dish-shaped parabolic concentrator is measured.The experimental results show the correctness of the theoretical analysis conclusion on the temperature,distribution and heat exchange efficiency of the heat absorber by different porous media materials.At the same time,the test results show that the large porosity structure of the same alumina material has higher heat exchange efficiency under different porosity conditions.However,under the same structure,when silicon carbide and alumina porous dielectric materials are used as heat sinks,the light-heat conversion efficiency of the silicon carbide porous dielectric materials is higher.