Study on filling materials and vacuum maintenance for vacuum insulation panels

Abstract

This study investigates a new type of Vacuum Insulation Panels (VIPs) as a superior thermal insulator, which is one of the most important components in future energy efficient buildings or refrigerators. The present research mainly focuses on two issues. One is on thermal transport mechanisms of VIPs with various filling materials, and the other is on vacuum deterioration mechanisms in VIPs. Firstly, three thermal transport mechanisms of various filling materials for VIPs are theoretically investigated with special emphasis on the solid conduction. As the first, the solid conductivities of porous materials such as a 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 reduced significantly. The above theoretical results show that the multi-layered staggered beam structure with radiation shields and the glass fiber arranged perpendicular to the heat flow direction are promising as the VIP’s filling material. A prototype of the staggered beam VIP is fabricated to show the practical applicability. Secondly, long-term vacuum maintenance characteristics are investigated for the VIP with an example of polymer staggered beam structure as the filling material. Various gas sources deteriorating the vacuum level in the staggered beam VIP are examined based on theoretical models and experiments. Gas permeation occurring through heat-sealed flanges in the barrier envelope is found to be the larges...