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Experimental determination of thermal conductivity of silica aerogel and two composite nano-porous insulation materials with the THS method
Gaosheng Wei, Yusong Liu, Xinxin Zhang, Fan Yu and Xiaoze Du
This paper dedicates to the experimental determination of thermal conductivities of silica aerogel, xonotlite-silica aerogel composite nano-porous insulation (X-SACNI) material and ceramic fibre-silica aerogel composite nano-porous insulation (CF-SACNI) material with the transient hot-strip (THS) method in different temperatures and pressures. The samples of silica aerogel, X-SACNI and CF-SACNI materials are firstly prepared. Two appropriative surroundings i.e. an elevated temperature surrounding from ambient temperature to 1450 K and a vacuum surrounding from atmosphere pressure to 10-3 Pa are designed for the THS method. Thermal conductivities of the prepared samples with different densities from ambient temperature to 723 K and 2 Pa to atmospheric pressure are then measured. The results show that both the thermal conductivity of silica aerogel and the two composite nano-porous insulation materials decreases significantly with the drop of pressure when p > 104 Pa, and almost reaches to a constant when p < 104 Pa. Both the thermal conductivity of silica aerogel and the two composite nano-porous insulation materials increase cubic with the rise of temperature. The thermal conductivity of silica aerogel has a minimum value when the density is about 145 kg/m3. The effective thermal conductivity of xonotlite-type calcium silicate and ceramic fibre can be lowered greatly by composite with silica aerogel. The thermal conductivity measurement uncertainty is estimated less than 3 percent at ambient temperature.
Keywords: Aerogel; insulation material; porous media; thermal conductivity; transient hot-strip method; xonotlite.