Bubble modulation using acoustic standing waves in a bubbling system

The behavior of a 6 mm mesobubble in an acoustic standing wave field is examined both experimentally and numerically in this study. The acoustic standing waves at 16 and 20 kHz are generated using two Nickel magnetostrictive transducers located at the top and bottom of the column. Experimental studies of the rise velocity of a mesobubble in the acoustic field indicate an axial wavy rising pattern of the bubble synchronized with that of the standing wave. The bubble rise velocity is significantly lower than that in the absence of an acoustic field. The behavior of bubble volume contraction and expansion can be accounted for by a 3-D direct numerical simulation of the bubble dynamics and flow field based on the compressible N-S equations coupled with the level-set method. The experiments and simulation reveal a consistent value of the ratio of the Bjerknes force to the buoyancy force for a single mesobubble rising in the acoustic field to be at 20-25%.