The thermal conductivity of ceramic powder packed beds was measured at temperatures below 100 °C for various powder sizes and compositions and under different gas atmospheres. Measurements at low pressures (down to 10 Pa) combined with a theoretical model allowed the elucidation of geometrical and thermal resistance parameters for the contact points between granules. The gap thickness and contact point size were found to be well correlated with the mean particle size. The thermal conductivities of all powders at low pressure were found to differ at most by a factor of two, whereas the solid‐phase conductivities of the powder materials differed by more than one order of magnitude. A theoretical model accounting for the size‐dependence of contact point conductivity is incorporated to rationalize this trend.
Vibrational motion and dynamics of two-dimensional layers composed of identical inelastic solid disks are investigated experimentally and characterized in terms of the dimensionless acceleration. Several vibrational regimes with different degrees of vibrofluidization are studied by means of the layers' videorecordings and tracking the motion of one larger disk immersed into each bed of smaller particles. It is shown that depending on the vibrational acceleration, the larger disk either ultimately rises on top of the layer or vigorously moves throughout it, thereby indicating possibilities for efficient mixing. In a certain narrow range of the vibrational acceleration the layer is observed to repack and move as a single block. This acceleration range is well described by the model of an absolutely plastic body moving above a vibrated plate. Small deviations from this acceleration range lead to a significant layer expansion and distortion of its upper surface due to transverse waves. The vibrofluidization regimes are also characterized by measuring the force acting on the vessel's bottom and the time of its contact with the layer. The propagation speed of the compression-expansion waves is estimated and found consistent with the predictions of our earlier semiempirical and analytical models.
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