Simulation And Simulation Of The Effective Thermal Conductivity Of Hollow Microsphere Gold Foam At Low Temperature

Hollow microsphere foam metal with both open and closed cell foam characteristics consists of closed pores in the sphere and gaps between sintered spheres.This kind of material has the characteristics of low density and low thermal conductivity,and is widely used in sound insulation,heat insulation,catalysis and electromagnetic shielding.Because of its high atomic number and low density,gold metal foam plays an important role in inertial confinement fusion(ICF)physics experiments:As a cavity material,it can effectively improve the laser-X conversion efficiency and suppress plasma expansion,and obtain a higher black hole radiation temperature.Under the condition of certain refrigeration power,the low temperature thermal conductivity of gold foam will directly determine whether the temperature difference of the inner wall of the cylinder meets the target 's physical design requirements.The experimental measurement of gold foam's effective thermal conductivity at low temperature has to overcome contact heat resistance and weld surface defects.However,because of its low mechanical strength,the hollow microsphere stacked structure gold foam has not been tested for its nondestructive micromanipulation technology.Therefore,it is necessary to study the effective thermal conductivity of low density gold foam by means of mathematical model or finite element simulation.In order to solve the problems of modeling,finite element analysis and simulation results of stacking structure,the following research works have been carried out in this paper:(1)The effective thermal conductivity of hollow microsphere foam structure in two-dimensional plane is derived through the equivalent thermal conductivity method of unit structure model.The relationship between effective thermal conductivity and heat conduction in the sphere,heat conduction outside the sphere and solid phase heat conduction is obtained.The analytical results show that the effective thermal conductivity of the hollow microspheres is only related to the diameter of the sphere,the thickness of the spherical shell and the interleaving angle when the thermal conductivity is kept constant and the random stacking is not considered.(2)Using the Python script interface of Abaqus for the second development,a random stacking model of hollow microsphere structure foam gold was established.Compared with the SEM of hollow microsphere gold foam,it is found that the microstructure is similar,but there are lots of nano-pore structure on the sphere's wall.The modeling problem of the random stacking structure of the opening of the sphere's wall is solved by the method of opening small holes on the shell of sphere.Developed a human-machine interaction interface,which integrates all parameter input,model establishment,boundary conditions and contact conditions.And it greatly improved the efficiency of modeling and computation,and enhanced the universality of the computing process.(3)Through the finite element analysis,the influence conditions of effective thermal conductivity of the hollow microsphere gold foam are obtained,including the inner diameter of the ball,the thickness of the spherical shell,the porosity,the aperture of the hole and the thermal conductivity of the flow phase.It is found that the effective thermal conductivity decreases with the increase of inner diameter and increases with the increase of shell thickness.The porosity increases and the effective thermal conductivity decreases.When the porosity is greater than 98%,the effective thermal conductivity will decrease sharply.Compared with 98%before,the effective thermal conductivity decreases by 4 times.The thermal conductivity of the flow phase has great influence on the effective thermal conductivity of the gold foam.When the flow phase is air,the thermal conductivity increases by 16%,and the thermal conductivity increases 131.2%when the flow phase is water.In vacuum,the small hole on the spherical shell has little effect on the effective thermal conductivity,and the average relative error calculated under different apertures is 0.021,(4)Through a large number of computational structural analysis,it is found that there is a deviation in the calculation of the model under the same geometric parameter.The analysis shows that due to the scale of random models,the location of random balls will affect the calculation results.The results of finite element calculation are fitted by regression models of various regression models in machine learning to reduce the difference of calculation results caused by the difference of the distribution difference of each modeling ball,and a relatively stable calculation result is obtained.