Bubbling characteristics of sound-assisted fluidized beds

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 conditi ons both near and above minimum bubbling. Experiments were performed with p owders of density ranging from 1.1 g/cm(3) to 3.95 g/cm(3) and particle siz e ranging from 11 to 80 mum. A loudspeaker positioned at the top of the col umn generated the acoustic field. The sound pressure at the distributor plate was used to characterize the pr essure distribution throughout the bed. It was found that high intensity so und disrupted the cohesive nature of the powders, permitting both homogeneo us 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 s ound pressure level, particle density and particle size. In addition, the d ata show the sound pressure level also affects bubble size. The bubble freq uency depends most strongly on the excess gas velocity and the basic bubbli ng mechanism remains similar to that of larger particles without sound. (C) 2001 Elsevier Science B.V. All rights reserved.