A study on rigid foam/evacuated powder composite panels for thermal insulation

Abstract

The present study investigates the feasibility of a composite panel: a series of individually evacuated panels incapsulated in a rigid closed cell foam matrix. The panels were encapsulated in a thin glass sheet barrier to preserve the vacuum. Glass has been chosen as the barrier material because it has a relatively low thermal conductivity and it is effectively impermeable to all gases. Low cost perlite powder has also been used, because its thermal conductivity is very similar to the thermal conductivity of other finer and more expensive powders, such as silica provided that low pressures are maintained within the panel by using a glass gas permeation barrier. The individual plastic-enclosed evacuated powder panels encapsulated in a thin glass barrier, have been put together in a matrix structure so that even if one individual panel is punctured or damaged, the insulating performance of the entire matrix is not significantly affected. Individual powder panels were produced and tested in this study. The thermal conductivity of the individual panel was found to be 0.0062 W/m·K. The composite foam block with embedded vacuum panels achieved an overall thermal conductivity of 0.01656 W/m·K for a 4.2 cm thick composite block. The polyurethane foam used above foam block had a thermal conductivity of 0.024 W/m·K. Numerical analysis has indicated that by using low conductivity foam and more optimal vacuum panel geometries, much lower overall conductivities can be achieved.