Apparent thermal conductivity of silica aerogels, which are the best candidate of transparent insulating materials, was measured by the newly developed thermal conductivity equipment using guarded hot plate absolute method. The measurements were carried out as a function of the temperature and the boundary emissivity. Radiative heat transfer through the aerogel samples is calculated with a simple model using the spectral transmission data. Calulated results well explained the measured variations of the apparent thermal conductivity with the temperature and the boundary emissivity.
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