Numerical predictions of thermal conductivities for the silica aerogel and its composites

Abstract

In the present paper, two kinds of microstructures are reconstructed for silica aerogels by diffusion-limited cluster-cluster aggregation (DLCA) method and open-cell structure generation method. The discrete ordinate method is adopted to solve radiative transfer equation, and the lattice Boltzmann method (LBM) is adopted to solve the conduction-radiation equation to predict the effective thermal conductivity considering the combined contribution of conduction and radiation. The partial bounce back scheme for thermal LBM is extended to consider the thermal contact resistance between two contact components with different thermal conductivity in aerogels. To validate the accuracy of the present model, some corresponding experimental measurements based on Hot Disk method are conducted. The results show that: the open-cell structure is more suitable for the real aerogel microstructure than DLCA structure; the effective thermal conductivity of the pure aerogel increases rapidly with temperature and is greatly suppressed if additives are doped; the Rosseland equation will over-predict the effective thermal conductivity of pure aerogels, especially at high temperature, but it can be applied for aerogel composites if the optical thickness assumption is satisfied; the thermal contact resistance in aerogels has a significant influence on their effective thermal conductivity, and a larger thermal contact resistance leads to a smaller effective thermal conductivity.