Mass transfer of acoustic cavitation bubbles in multi-bubble environment

The mass transfer around acoustic cavitation in a multi-bubble environment was numerically studied. To model the multi-bubble environment, several bubbles were placed at the vertices of the polyhedron, and one bubble was placed at the center, and then an ultrasonic pressure wave with a frequency of 20 kHz was imposed along the simulation boundary box. In this study, the mass transfer of chemical species that were initially present only in the bubbles was investigated. The numerical simulation revealed that the mass transfer to the outside bubble was enhanced by the bubble translational motion caused by the secondary Bjerknes force, whereas the mass transfer to the outside bubble increased during the bubble compression period, and the mass transfer to the inside bubble increased during the bubble expansion period. In addition, the mass transfer to the outside bubble was enhanced, particularly for the nonspherical bubble motion during the bubble compression period. The mass transfer to the outside bubble increases with a denser bubble arrangement, which can be explained in terms of the cover ratio, which is defined as the ratio of the projected area of the surrounding bubbles to the central bubble.