Lattice Boltzmann Method Simulation Of The Aerogel Nano Thermal Insulation Composites Heat Conduction

As a kind of"super insulation material",the microscopic structural characteristics of aerogel make its heat insulation efficiency much higher than that of traditional materials,and it can be widely used in industrial buildings and military aerospace fields.The understanding of the microscopic heat transfer mechanism of aerogel and its composites is of great significance to the field of thermal insulation design and its own development and utilization.In this paper,the Lattice Boltzmann method（LBM）is used to numerically simulate aerogel and its composites under microscopic conditions.The thermal conductivity of aerogel on a two-dimensional plane was modeled to explore the boundary temperature jump caused by the change of characteristic scaleL_x in the mirror bounce format.The variation of aerogel temperature distribution with characteristic scaleL_x was investigated in the diffuse rebound format.The influence of bounce ratio coefficient_br on the temperature distribution and thermal conductivity of aerogel in mixed bounce format was discussed,and the difference of thermal conductivity in mirror bounce format and diffuse bounce format was compared and analyzed.The structure of aerogel porous media was obtained by random four-parameter generation method,and the influence of porosity D and pore size on the temperature distribution and thermal conductivity of porous media was explored by LBM.The thermal conductivity model of fiber-aerogel composite was constructed and equivalent treatment was carried out to investigate the temperature distribution and thermal conductivity variation of the composite under different fiber proportions.Verify the feasibility of the local mesh encryption model based on the theory of region splitting in the calculation of thermal conductivity of composite materials,and use the region splitting model combined with LBM to conduct numerical simulation of equivalent composite materials,explore the influence of different material regional scale,so as to obtain the temperature distribution characteristics of composite materials and the change law of thermal conductivity.The results of this paper show that the temperature distribution varies with the characteristic scaleL_x under different boundary conditions for the simulation of thermal conductivity of aerogel.The temperature changes linearly in the specular reflection format,while the temperature changes in the diffuse emission boundary format,and the step change occurs in the temperature transfer process,and the step phenomenon gradually disappears with the decrease of the bounce ratio coefficient r_b.The difference of internal structure also affects the thermal conductivity of aerogel:the temperature distribution of aerogel gradually tends to the temperature distribution of uniform medium with the increase of porosity D or the decrease of pore size.When simulating the thermal conductivity of fiber-aerogel composite,the higher the fiber contentφ_f in the composite,the more uneven the temperature distribution and the higher the thermal conductivity.The local mesh encryption model can reduce the number of gridsψand improve the computational efficiency when dealing with composite materials.When the region splitting method is used for simulation,the boundary of the aerogel region will appear obvious temperature jump,and the temperature jump phenomenon of the fiber region gradually decreases to disappear with the increase of its own scaleL_x,f.The temperature distribution in the aerogel region and the temperature at the material junction increased with the increase of the fiber scaleL_x,f,while the temperature jump（35）T at the junction decreased with the increase of the fiber scale.The thermal conductivity of the composites showed different scale effects with the change of the scale of the two materials.