Effect of Temperature on Fluidization of Geldart's Group A and C Powders: Role of Interparticle Forces

The interest in handling granular materials in a variety of industrial processes carried out at high temperature raises the question of how this variable affects the fluidization quality not only in the case of cohesive particles, belonging to Geldart's C powders, but also of powders classified as A. The aim of this work is, therefore, to study, from both an experimental and phenomenological point of view, the effect of temperature on the fluidization of two different powders belonging to groups A and C of Geldart's classification. In particular, fluidization tests were performed at different temperatures (20-800 °C) and using acoustic fields of different intensities (130-150 dB) and frequencies (50-200 Hz) to highlight the influence of interparticle forces (IPFs) on the fluidization quality with increasing temperature. Pressure drops and bed expansion curves were elaborated to show the influence of temperature on minimum fluidization velocity and size of fluidized particles. Then the validity of different correlations available in literature to predict the minimum fluidization velocity at high temperature was assessed. Finally, the experimental findings were interpreted from a phenomenological point of view on the basis of the cluster/subcluster model, which can account for temperature effects on both hydrodynamic and cohesive forces. In particular, the proposed model made it possible to directly evaluate IPFs, thus explaining the fluidization behavior of the powders on the basis of the intensification of their cohesiveness with increasing temperature.