Bubbling characteristics of sound-assisted fluidized beds

Abstract

Low frequency sound has been used to promote fluidization of fine cohesive powders in a 0.15-m I.D. column. The bed was fluidized with air at conditions both near and above minimum bubbling. Experiments were performed with powders of density ranging from 1.1 g/cm 3 to 3.95 g/cm 3 and particle size ranging from 11 to 80 μm. A loudspeaker positioned at the top of the column generated the acoustic field. The sound pressure at the distributor plate was used to characterize the pressure distribution throughout the bed. It was found that high intensity sound disrupted the cohesive nature of the powders, permitting both homogeneous and bubbling fluidization. The sound expanded the bed up to the onset of bubbling. The data show the minimum bubbling velocity is affected by the sound pressure level, particle density and particle size. In addition, the data show the sound pressure level also affects bubble size. The bubble frequency depends most strongly on the excess gas velocity and the basic bubbling mechanism remains similar to that of larger particles without sound.