THERMAL CONDUCTIVITY OF POROUS SYSTEMS

Predicted formulae are given for the determination of the effective thermal conductivity of powdered and solid porous materials in a wide temperature range and various gas media. The calculated values of the effective thermal conductivities of about 100 various materials are compared with the experimental values of different authors including the authors of the paper. The methods for calculating the effective thermal conductivity of powdered mixtures, in particular of Al2O3 and powdered plexiglass mixture, are set forth. It is shown that mixing different powdered materials can change the effective thermal conductivity of fillings over wide ranges for various gases. This is mostly essential for powdered materials at low temperatures when thermal conductivity of particles becomes close to that of gases in the pores. This also refers to contact thermal conductivity of vacuum-powder thermal insulation at low temperatures where the contact thermal conductivity on external mechanical load, the elasticity of the material and the state of the material surface, appear as a dominating factor. Experimental and calculated data on thermal properties of solid porous systems (chamotte ceramics) are given for a wide temperature range and various gas media. © 1968.