Analysis Of Radiation With Its Coupling Heat Transfer Process Of Solar Optical Window And High Temperature Molten Salt

For the unlimited reserves and cleanliness in utilization,solar energy has become an excellent alternative energy to solve the problems caused by the overuse of fossil fuels,such as energy shortage,environmental pollution and greenhouse effect etc.However,due to the regular limiting factors such as diurnal variation,season changes and latitude differences as well as random limiting factors such as weather changes,there are uneven distribution and unsustainable supply problem in the development of solar energy.It is the key problem in the utilization of solar energy to find an appropriate energy storage method that discontinuous energy can be transformed into stable and continuous energy supply.Therefore,radiation and coupling heat transfer of high temperature molten salt and solar optical window in solar high temperature heat utilization field are studied numerically in this paper.Based on the background of the high temperature utilization of solar energy,with the molten salt and solar optical window taken as the research object,a finite element model of the radiation and coupled heat transfer process was established by MATLAB programming combined with commercial software Fluent.First of all,ignoring the radiative heat transfer,a coupled heat transfer model of conduction and convection for high temperature molten salt was established;the heat transfer process of high temperature molten salt in tubular heat collector was studied;the effect of heat flux distribution,convective heat transfer coefficient and inlet velocity on the temperature field distribution was analyzed.All of these studies provide the necessary basis for the subsequent research of coupled heat transfer process within the radiative heat transfer.Secondly,based on the coupled heat transfer model of heat conduction and convection,considering the radiative heat transfer,a more complex coupled heat transfer model consist of the radiation,conduction and convection for high temperature molten salt was established,where influence of the radiative transfer characteristic parameters(such as the albedo and refractive index)and boundary conditions(such as the heat flux,entrance velocity)was investigated.Then,based on the mathematical description of variation of thermo-physical parameters with temperature,a finite element model of coupled heat transfer consist of radiation,conduction and convection was established,and the influence of radiative heat transfer on temperature field of molten salt was mostly analyzed.Finally,a coupled heat transfer model of radiation-conduction was established to solve the solar optical window;the temperature field distribution of solar optical window was simulated,the effects of radiation,boundary conditions and physical parameters on the coupled radiation-conduction temperature field were investigated.The results show that radiative heat transfer occupies a very large proportion in the process of coupled heat transfer between the solar optical window and high temperature molten salt that cannot be ignored.The calculation result of the temperature field of molten salt when radiative transfer characteristic parameters changes with the temperature shows the maximum temperature deviation reaches 50.7% considering the radiative heat transfer model or not.Considering the radiative heat transfer,the temperature of the solar optical window is effectively reduced,and the maximum temperature deviation reaches 17%.