Studies on Thermal Conductivity Measurement of Granular Materials in System of Solid-Fluid Mixture

Abstract

The hot wire method has been used to measure thermal conductivity of massive solid materials. In order to find out a suitable way to measure thermal conductivity of granular solid materials, Ks, by hot wire method, the authors have examined the thermal conductivity measurement about the system of dispersed granular solid materials into a solid dispersion medium like silicon rubber. However, there were some limitations in the method that silicon rubber didn't work well at higher temperatures than 300°C and the rubber penetrated into the pore of granular solid materials in some cases. In this research, the authors tried to use some fluids to be applicable at higher temperatures and not to react with granular solid materials, and developed a method to be able to calculate Ks from gross thermal conductivity of granular solid-fluid mixture, K, and that of Kf.For the calculation of Ks from K and Kf, de Vries'equation was reasonably applied to both spherical and irregular-shaped particles. The shape factors Gi included in de Vries'equation were found to vary with the surface area of the granular solid materials in the case of spherical particles, but was almost constant in the irregular shaped particles.They wereG1=G2=5.34×10-4S+0.0374 G3=-1.07×10-3S+0.925} for spherical particle, G1=G2=0.05, G3=0.90 for irregular shaped particle, where S is surface area (cm2/cm3)The reliability of the results obtained by the application of de Vries' equation increased with the use of fluid having higher thermal conductivity. For example, when helium gas with thermal conductivity of 3.65×10-4cal/cm⋅sec⋅°C was used, the error of the obtained values Ks of 3.25×10-3 and 1.4×10-2cal/cm⋅sec⋅°C were about 4% and 8%, respectively.In view of the fact that the error increased with increasing thermal conductivity of granular solid materials to be measured, this method can be applied to the solid materials having thermal conductivity of smaller than about 1.5×10-2cal/cm⋅sec⋅°C, if the error of ±10% is allowable.