title: Interacting bubble clouds and their sonochemical production.
abstract: An acoustically driven air pocket trapped in a pit etched on a surface can emit a bubble cluster. When several pits are present, the resulting bubble clusters interact in a nontrivial way. Fernández Rivas et al. [Angew. Chem. Int. Ed. 49, 9699-9701 (2010)] observed three different behaviors at increasing driving power: clusters close to their "mother" pits, clusters attracting each other but still well separated, and merging clusters. The last is highly undesirable for technological purposes as it is associated with a reduction of the radical production and an enhancement of the erosion of the reactor walls. In this paper, the conditions for merging to occur are quantified in the case of two clusters, as a function of the following control parameters: driving pressure, distance between the two pits, cluster radius, and number of bubbles within each cluster. The underlying mechanism, governed by the secondary Bjerknes forces, is 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 understanding the experimental observation that, above a certain power threshold, any further increase of the driving does not improve the sonochemical efficiency.
authors: Physics of Fluids Group, Faculty of Science and Technology, Impact and Mesa+ Institutes & Burgers Center for Fluid Dynamics, University of Twente, 7500AE Enschede, The Netherlands. l.stricker@utwente.nl
authors: Laura
authors: L
authors: Stricker
authors: Benjamin
authors: B
authors: Dollet
authors: David
authors: D
authors: Fernández  Rivas
authors: Detlef
authors: D
authors: Lohse
mesh_terms: D000388:Air; D005609:Free Radicals / Q000737:chemistry; D016014:Linear Models; D045423:Microbubbles; D008956:Models, Chemical; D017711:Nonlinear Dynamics; D009991:Oscillometry; D010316:Particle Size; D011312:Pressure; D012825:Silicon / Q000737:chemistry*; D013016:Sound; D013499:Surface Properties; D014465:Ultrasonics; D014867:Water / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D014867:Water; D012825:Silicon