Researches On The Performance Optimization Of Porous Thermal Insulation Materials

The effective thermal conductivity of porous materials is determined by pore shape? pore volume content?connectivity?distribution and thermal conductivity of gases and solids.Recent works were mainly focused on gas volume content and thermal conductivity of two-component.Previous works did not systematically study the synergistic effects of pore shape and connectivity.This paper focuses on the synergistic effect of pore shape and pore connectivity as well as the influence of the anisotropy and distribution.The research results can guide the optimal design of porous insulation materials.The results show that the thermal conductivity of the porous thermal insulation material decreases with the increase of the pore volume content for all the pores.In the two-dimensional model,the thermal insulation performance of materials with various shaped pores is followed: I shaped > T shaped > triangular > square > spherical > rhombic > elliptical > rectangular.In the three-dimensional model,the thermal insulation performance of materials with various shaped pores is followed: I shaped > T shaped > rhombic > cube > spherical > cylindrical pore.Therefore,I shaped and T shaped pores are the best pore in decreasing thermal conductivity of porous materials.The longer the lengths of the pore perpendicular to the direction of heat flow,the better the thermal insulation performance of the pore.The length of the pore perpendicular to the direction of heat flow is a key factor in decreasing the thermal conductivity of porous materials,while the length of the pore in the direction of heat flow has little influence on the thermal insulation performance of the material.The specific rule of influence is: when the pores overlap in the direction perpendicular to the heat flow,the length of the pores in the direction perpendicular to the heat flow is increased,and the connection of the pores enhances the insulation performance of the material;when the pores overlap in the direction of the heat flow,the pores are reduced in the direction perpendicular to the heat flow the length in the heat flow direction and the connection of the pores reduce the insulation performance of the material.For anisotropic pores,when the heat flow enters perpendicular to the long axis of the pore,the material has the best insulation performance;when the heat flow enters along the long axis of the pore,the material has the worst insulation performance.In addition,the thermal insulation of porous material decreases with the increase of the thermal conductivity of gas.When the gas thermal conductivity is low,reducing the gas thermal conductivity can effectively enhance the thermal insulation performance of porous materials,while when the gas thermal conductivity is high,changing the gas thermal conductivity has little effect on the performance of porous materials.