Experiment and identification of thermal conductivity and extinction coefficient of silica aerogel composite

Highly porous silica aerogel composites have shown excellent potential as insulation materials for various insulation systems, the knowledge of their conductive and radiative properties is of essential importance. In this study, several experiments were performed to measure the transient heat transfer behavior of silica aerogel composite at temperature between 290 and 1090 K with various gas pressures ranging from 0.01 Pa to 100 kPa. The temperature dependent conductive part of thermal conductivity kc(T), and global extinction coefficient of the silica aerogel composite were simultaneously determined from the experimental temperature data by solving an inverse problem employing the genetic algorithm as optimization method. The retrieved conductive thermal conductivity fell within 0.013-0.032 W/(m·K), increased nonlinear with increasing gas pressure, and showed an approximate linear increasing trend as temperature increases. The global extinction coefficients were independent of gas pressure and showed relatively good agreement with those predicted from Mie theory. These properties could be used to predict the effective thermal conductivity keff(T) for evaluating thermal performance of the insulation systems, and to separate contributions of conductive and radiative heat transfer in silica aerogel composite at various temperatures and gas pressures.