Thermal radiation effect on the effective thermal conductivity of porous material by pore level numerical simulation

Porous materials have been used in many thermal related applications, owing to its salient thermal properties. The heat transfer characteristics of porous materials are usually described through effective thermal conductivity (ETC) based on the continuum approach. Thermal radiation contribution to the ETC at high temperature will be very important. At present, only very few works on pore level simulation of the ETC take thermal radiation into consideration. In this work, ETC of porous materials is calculated based on a developed pore level simulation method that takes into account the coupled conduction and radiation heat transfer. Effects of thermal conductivity of skeleton material, emissivity of skeleton material and temperature on the ETC are also analyzed, among which thermal radiation effects on the ETC are discussed. Results show that the ETC increases non-linearly with the increase of temperature, thermal conductivity and emissivity of skeleton for closed cell porous material due to thermal radiation contribution. For open cell porous material, the skeleton acts as a barrier of thermal radiation, which results in decrease of ETC with the increase of emissivity of skeleton. A third order polynomial type temperature dependence relation is proposed and demonstrated to well describe the nonlinear behavior of the ETC. This work brings new insight and helps the understanding of thermal radiation effect on heat transfer in porous materials.