The influence of the frequency of acoustic waves on sound-assisted fluidization of beds of fine particles

Abstract

Sound-assisted fluidization of nonfluent 0.5–45 μm catalyst particles has been studied with a 145 mm i.d. column. Different amounts of solids of weight W ranging from 1 to 3 kg have been charged in the column. A loudspeaker generated an acoustic field, above the bed, with a sound pressure level SPL (referred to 20 μPa) varying from 110 to 140 dB and a frequency f varying from 30 to 1000 Hz. The improvement of the quality of fluidization obtained with certain combinations of W, SPL and f has been attributed to the breakup of clusters originally forming the bed into subclusters. For given W and SPL, the ranges of frequency within which channel-free homogeneous fluidization could be obtained have been determined, and within these ranges the kinds of curves for sizes of subclusters d s as a function of the frequency have been outlined. The nonmonotonic form of these curves could not be explained by means of the original sound-assisted fluidization model, which assumes a rigid cluster-subcluster structure. The existence of elastic forces between clusters and subclusters, assumed by the cluster/subcluster oscillators model, yields theoretical d s versus f curves with the same trend as those from experiments.