A NONSTEADY METHOD FOR DETERMINATION OF THERMAL-DIFFUSIVITY AND THERMAL-CONDUCTIVITY OF POORLY CONDUCTIVE SOLIDS

It is proposed in this work, to evaluate experimentally: thermal diffusivity, a, and thermal conductivity, k, of poorly conductive materials. The method selected is based on transient heat conduction in solid media and seeks to determine the conditions under which the power series solution characterizing the transient heat equation can be simplified and approximated, with a great degree of accuracy, by the first term of the series. It is then possible, by obtaining the temperature history (profile) of a single arbitrary point in the solid media, to compute the values of a and k. The experimental procedure requires relatively low cost apparatus and measurement equipment easy to use. In addition, from a theoretical standpoint, the procedure is independent of the initial boundary condition (Temperature at t = 0) and of the temperature sensor location (length). Most important, a prior knowledge of density and heat capacity is not required for the determination of the thermal conductivity. Three different solid geometries (Cylindrical, spherical and cubic) and five materials (PMMA, HMWPE, POLYAMIDE 66, POM and PTFE) were selected for the measurements. The results compare favorably with actual reported steady state values, within 5 per cent or less. © 1991, Taylor & Francis Group, LLC. All rights reserved.