Aerogels for Thermal Insulation
The characteristic feature of aerogels which makes them suitable as efficient thermal insulations is their microporosity. Pore diameters within the aerogel structure in the range of 50 to 100 nm limit the mean free path of air molecules. Even at ambient air pressure the gaseous thermal conductivity within the aerogels is thus considerably lower than the conductivity of free air (0.026 W/mK). Fig. 1 depicts the variation of the thermal conductivity of a monolithic silica aerogel with the internal gas pressure  in comparison with an aerogel powder. The thermal conductivity of the monolithic aerogel is around 0.018 W/mK at ambient pressure (1 bar). When the sample is evacuated to pressures below 10 mbar, the gaseous conductivity is 0.007 W/mK.
KeywordsEffective Thermal Conductivity Silica Aerogel Carbon Aerogel Heat Transfer Mode Gaseous Thermal Conductivity
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