ISSN Online: 2377-424X
ISBN Print: 1-56032-797-9
International Heat Transfer Conference 11
ANISOTROPIC THERMAL CONDUCTANCE IN THIN LAYERS OF DISORDERED PACKED SPHERES
Resumo
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.