Effective thermal conductivity of various filling materials for vacuum insulation panels

Abstract

Three thermal transport mechanisms of various filling materials for Vacuum Insulation Panels (VIPs) are theoretically investigated with special emphasis on the solid conduction. As the first, the solid conductivities of porous materials such as powder, foam, fiber and staggered beam subject to external atmospheric compression are derived using simplified elementary cell models. The results show that the solid conductivities of the fiber and staggered beam insulation are lower than those of the powder and foam due to the relatively long thermal path. The second mechanism, i.e., gaseous conductivity shows the lowest for the fine powder among the considered materials due to its smallest pore size. The radiative conductivity as the last is calculated using the diffusion approximation. If radiation shields are installed for the staggered beam, the radiation effect can be lowered to a negligible order of magnitude. The predicted total effective conductivities suggest that the fiber and staggered beam structures are promisingly proper filling materials for VIPs. (C) 2009 Elsevier Ltd. All rights reserved.