SOUND-ASSISTED AERATION OF BEDS OF COHESIVE SOLIDS

Five cohesive solids have been aerated in beds activated by an acoustic field of 150 dB and 120 Hz. The solids included a catalyst, an ash, a talc and two titanium oxide pigments. Sauter particle diameters were 11, 8, 5, 0.3 and 0.16 mum for catalyst, ash, talc, TR-92 Tioxide and A-Hr Tioxide, respectively. The solids showed different particle surface geometries when observed under a scanning or a transmission electron microscope. Sound-assisted aeration gave rise to bubble-free fluidization only in the case of catalyst, ash and talc. Under these conditions, fluidization curves and bed expansion correlations were obtained. Experimental results have been explained on the basis of a cluster-subcluster model which assumes that large clusters of particles break up into fluidizable subclusters when external (drag plus inertial) forces induced by acoustic waves overcome internal cohesive (van der Waals) forces at contact points between particles.