Experimental Analysis on Thermal Conductivity of Rock

This paper carried out the experimental study on the thermal conductivity of rock in different depth by transient hot-strip method and the analysis on the reliability of the data. The results show that thermal conductivity of pelitic siltstone has been less affected by the varying versus depth of the rock stratum than tuff, but the thermal conductivity of tuff slightly higher than pelitic siltstone.

Gaseous Conductivity Study on Silica Aerogel and Its Composite Insulation Materials

This paper presents a theoretical and experimental study on gaseous conductivity of silica aerogel and composite insulation materials. First, the insulation material samples (including silica aerogel, xonotlite-type calcium silicate, xonotlite-aerogel composite, and ceramic fiber-aerogel composite) were prepared. Next, the gaseous conductivities of the prepared samples were measured from 0.045 Pa to atmospheric pressure using the transient hot-strip (THS) method. The gaseous conductivity expressions obtained based on the kinetic theory were then compared with the experimental results. It is shown that the gaseous conductivity of both xonotlite-type calcium silicate and silica aerogel decreases significantly with decreasing pressure. The gaseous conductivities of xonotlite-type calcium silicate and silica aerogel reach zero at about 100 Pa and 104 Pa, respectively. The theoretical gaseous conductivity expressions match well with the experimental results of xonotlite-type calcium silicate and silica aerogel but not with the experimental results for the composite insulation materials. This mismatch indicates that the aerogel does not totally fill the original interspace of the xonotlite-type calcium silicate and ceramic fiber in the two kinds of composite insulation materials.

Theoretical Study on Transient Hot-Strip Method by Numerical Analysis

This paper presented the effects of finite dimensions of the sample and nonzero heat capacity of the strip on thermal conductivity determination with the transient hot-strip method. Through the numerical analysis of the temperature field within the system composed of the samples and the strip, the temperature transients at the strip surface were obtained to calculate the thermal conductivities of materials, which were compared with the exact values. The effect of heat losses out of the external surfaces of the sample and the heat capacity of the strip on thermal conductivity determination were then analyzed comprehensively. It is shown that the sample finite dimensions have a great effect on thermal conductivity determination, especially on the materials with relatively higher thermal diffusivities, and the measured thermal conductivity is always lower than the exact value due to the lower convective heat transfer coefficient out of the external surfaces of the sample. The measurement error is estimated to be less than 2.1% for the material with thermal diffusivity less than 4.0×10−6 m2/s with the sample dimensions of 120×60 mm2(width×thickness) and the fitting time interval of 20–300 s. The nonzero heat capacity of the strip has a great effect on thermal conductivity determinations of the materials with relatively lower thermal diffusivities. The measurement error is estimated to be less than 5% for the material with thermal diffusivity larger than 0.8×10−7 m2/s with Cr20Ni80 alloy as the strip.

Gaseous Conductivity Study on Silica Aerogel and Its Composite Insulation Materials

This paper presented theoretical and experimental study on gaseous conductivity of silica aerogel and it’s composite insulation materials. The samples of silica aerogel, xonotlite-type calcium silicate, xonotlite-aerogel composite and ceramic fibre-aerogel composite insulation materials were prepared firstly. The gaseous conductivities of the prepared samples were measured from 0.045 Pa to atmospheric pressure with the transient hot-strip (THS) method. The gaseous conductivity expressions based on the kinetic theory were then compared with the experimental results. It is shown that both the gaseous conductivity of xonotlite-type calcium silicate and silica aerogel decreases significantly with the drop of pressure. The gaseous conductivity of xonotlite-type calcium silicate reaches to zero at about 100 Pa and the gaseous conductivity of silica aerogel reaches to zero at about 104 Pa. The theoretical gaseous conductivity expressions match well with the experimental results of xonotlite-type calcium silicate and silica aerogel respectively, but do not match with the experimental results for the composite insulation materials. It indicates that the aerogel does not fill the two kinds of composite insulation materials entirely, and some micro level pores still exist in them.