A majority of the energy consumed by the average household is used for space heating and cooling. Typically, these buildings are equipped with fiberglass and polystyrene foam insulation. In order to reduce energy consumption, vacuum insulation panels (VIP) were developed. Although VIPs provide high performance heat insulation, they are much more expensive relative to traditional insulation mainly due to the use of fumed silica as the core material. Hence, the goal of this research is to devise a low cost core material, which would allow widespread implementation of VIPs. Diatomaceous earth and glass bubbles were studied for their potential as VIP core materials. The pore size distribution and structure of these materials were examined by mercury porosimetry, nitrogen sorption, and scanning and transmission electron microscopy. Composites fumed silica with the addition of these materials were made by dry pressing. Our results showed the possibility of fabricating low cost composites that have comparable performance with pure fumed silica. Through measuring the thermal conductivity of granular materials of different compositions, a trend was observed between the intrinsic solid thermal conductivity and effective thermal conductivity of the granular solid. We demonstrate a method of calculating the intrinsic solid thermal conductivity from effective thermal conductivity, which is measured experimentally. The calculated results were found to be in good agreement with values reported in the literature. This method provides a practical alternative for the determination of thermal conductivity of solid materials, which are difficult or costly to prepare for direct measurements.
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