In-plane conductive heat tansfer in solid and porous planar structures

Abstract

Methods for determining the in-plane thermal diffusivity in a planar sample geometry were developed. These methods were tested and verified by measuring planar metal samples with known thermal properties. The techniques used were based on heating the sample at one edge and recording the evolution of the temperature field in the sample by a thermographic camera. The temperature fields at different times were processed and then fitted by a solution to a heat equation describing the experimental setup, thermal diffusivity as one of the fitting parameters. In the first experimental setup the sample was placed in a weak constant flow of air, and the situation was improved in the second setup by placing the sample in a vacuum chamber, where convective heat transfer was totally removed. After verification measurements, the latter setup was applied to porous sintered bronze samples, and their effective thermal conductivities were determined. The sintered samples were also imaged by X-ray microtomography so as to obtain a 3D model for their structure. It was shown that the effective thermal conductivity of the samples could be predicted by an analytical expression which involved certain parameters determined from the 3D images. Finally, as another application of the heat equation, propagation of temperature profiles in the form of slow-combustion fronts were studied in sheets of paper. The dynamical properties of these fronts belong to the KPZ universality class, for which theoretical results are available for the height-fluctuation distributions. Height fluctuations for such fronts were determined experimentally, and their distributions were found to be well fitted by corresponding theoretical distributions.