Comparative study of a cubic, Kelvin and Weaire-Phelan unit cell for the prediction of the thermal conductivity of low density silica aerogels

Abstract

Super insulating porous materials such as silica aerogels have remarkable thermal insulating properties as demonstrated, experimentally. However, unravelling the underlying heat transfer phenomena is difficult because of the complex multiscale 3D structure of aerogels. For densities higher than 150 kg.m−³, there is a good correlation between experimental and predicted thermal conductivity values based on cubic unit cells. However, below 150 kg.m−³, large discrepancies between measured and predicted thermal conductivity values still exist. This numerical study tackles this issue by predicting thermal conductivities of silica aerogels including solid, gaseous and radiative heat transfers using more representative shaped unit cell types (Kelvin and Weaire – Phelan cells). The effects of the pore size distribution and their shape could then be analyzed. A parametric study was carried out including the skeleton and neck size, the gas void dimension and the contact length between the beads with respect to the density and was benchmarked against available literature. For the investigated range of densities, good agreement was found between the predicted results obtained using these newly applied unit cell geometries and previously measured experimental data.