Conduction of heat in powders

Abstract

While regular use is being made in industry of the thermal insulating properties of powders and other fibrous or cellular materials, the physical principles underlying the processes of heat transfer through such bodies have not received much attention. The problem, in regard to powders, has been studied by Smoluchowski in 1911, and later by Aberdeen and Laby. Smoluchowski’s investigation included the effect of such factors as the grain size, the kind, and density of the gas on the conductivity of powders of different materials. The experimental procedure followed in his work is unfortunately open to serious objections, and in consequence the data obtained by Smoluchowski are probably not reliable. Further the method, a cooling one, could not be applied to powders having high conductivities. In this laboratory, Aberdeen and Laby have studied the conductivity of the insulating powder silox filled with several gases, as a function of the gas pressure. The powder was contained between two concentric cylinders and the heat transfer was measured across a central portion where the flow was shown to be strictly radial. Platinum thermometry was used so that reliable data are to be expected. Their experiments, however, were limited to a single powder, and, at the suggestion of Professor Laby, a more extensive investigation using powders of different materials and of various grain sizes has been undertaken.