Effect of Radiation on Heat Transfer in Open-Cell Foams at High Temperature

There are a variety of foams that can be used in thermal protection and/or thermal insulation systems. At high temperature (> 1000 K) thermal radiation may be important or dominate heat transfer in the foam; however, studies based on more detailed thermal radiation analysis are limited. In this paper foams are considered to be semitransparent, because radiation can penetrate through the pore (or void) space and/or foam skeleton (solid matrix), depending on the materials from which the foams are made. Of particular interest of this study is to understand how the properties such as foam material its density, porosity, etc. affect thermal and radiant energy transfer. Physical and mathematical models are developed to account for conduction and radiation (absorption, emission and scattering) in the porous material. The spectral extinction coefficients of SiC foams are measured experimentally in the laboratory at room temperature, and the radiative transfer equation is solved using the spherical harmonics P₁ and the Rosseland diffusion approximations. Parametric calculations have been carried out, and the results are reported in the paper for a range of parameters characterizing heat transfer in SiC foams of different porosities to identify desirable conditions for effectively reducing heat transfer in potential thermal protection concepts.