Interacting bubble clouds and their sonochemical production

TL;DR

This paper investigates how interacting bubble clouds formed by trapped air pockets influence sonochemical production, revealing that nonlinear bubble oscillations and secondary Bjerknes forces significantly affect bubble behavior and radical generation.

Contribution

It demonstrates that nonlinear bubble oscillations and secondary Bjerknes forces govern bubble interactions, impacting sonochemical efficiency and providing insights for optimizing bubble cluster behavior.

Findings

Secondary Bjerknes forces influence bubble cluster dynamics.

Nonlinear oscillations dampen bubble activity and radical production.

Increasing power beyond a threshold does not enhance efficiency.

Abstract

Acoustically driven air pockets trapped in artificial crevices on a sur- face can emit bubbles which organize in (interacting) bubble clusters. With increasing driving power Fernandez Rivas et al. [Angew. Chem. Int. Ed., 2010] observed three different behaviors: clusters close to the very pits out of which they had been created, clusters pointing toward each other, and merging clusters. The latter behavior is highly undesired for technological purposes as it is associated with a reduction of the radical production and an enhancement of the erosion of the reactor walls. The dependence on the control parameters such as the distance of the pits and the conditions for cluster-merging are examined. The underlying mechanism, governed by the secondary Bjerknes forces, turns out to be strongly influenced by the nonlinearity of the bubble oscillations and not directly by the number of nucleated bubbles. The Bjerknes forces are found to dampen the bubble oscillations, thus reducing the radical production. Therefore, the increased number of bubbles at high power could be the key to understand the experimental observation that, after a certain power threshold, any further increase of the driving does not improve the sonochemical efficiency.