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ISSN Online: 2377-424X

ISBN Print: 1-56032-797-9

International Heat Transfer Conference 11
August, 23-28, 1998, Kyongju, Korea

ANISOTROPIC THERMAL CONDUCTANCE IN THIN LAYERS OF DISORDERED PACKED SPHERES

Get access (open in a dialog) DOI: 10.1615/IHTC11.690
pages 33-38

Abstract

The thermal conductance of packed spheres has been extensively investigated in the past, but the effect of packed-layer thickness on thermal conductivity and the physical mechanism of this effect have never been studied before. This work analyzes the effect of thickness on the thermal conductivities of packed-sphere layers based on statistical distributions of unit packing cells of spheres. Percolation and effective-medium approximation approaches are used to calculate the thermal conductivities in the directions perpendicular and parallel to the packed-layers. As in the case of thin solid films, the thin packed-sphere layers exhibit anisotropic thermal conductivity. The effect of packed-layer thickness on the variation of the thermal conductivity, however, has a different trend than that of thin solid films. With a reduction in thickness, the perpendicular thermal conductivity increases while the parallel conductivity decreases. In contrast to the thin solid film case, the packed-sphere thickness effect is due to the random distribution of the packed spheres, not to a limitation of the mean free path of the main heat carriers. The results indicate that the thickness effect becomes appreciable when the packed-layer thickness is less than 10 times the sphere diameter. A dramatic thickness effect is anticipated in disordered composites with very different component conductivities.