A review on heat transfer in nanoporous silica aerogel insulation materials and its modeling

Silica aerogels are widely used in many fields for thermal insulation, such as building insulation, electric power energy, energy storage systems, and high-temperature thermal protection due to their excellent insulation performance. Therefore, the heat transfer in silica aerogels and its modeling in recent years have attracted much attention and many valuable achievements have been acquired. The heat transfer in nano-porous silica aerogels and its modeling methods are reviewed in this work. This review starts with a brief introduction of heat transfer characteristics in silica aerogels, including the multi-component and multi-mode coupling effect, size effect, and multiscale effect. Then the heat transfer mechanism of each mode, including heat transfer via gas phase, solid phase, and thermal radiation, is reviewed, and the models for predicting the gaseous thermal conductivity in nanoscale pores, gas-contributed thermal conductivity, the apparent thermal conductivity of solid skeleton, and finally the effective thermal conductivity are collected and discussed in details. Besides, modeling of transient heat transfer in silica aerogels is also briefly introduced. Finally, the conclusions and some problems which need to be further investigated in the future are provided.