Free Surface Enhancement of Droplet Rupture by Cavitation Bubble Collapse

TL;DR

This study investigates how cavitation bubbles cause droplet rupture in confined environments, deriving a scaling law that predicts rupture based on bubble and droplet parameters, with implications for engineering and biomedical applications.

Contribution

The paper introduces a non-dimensional Kelvin impulse-based scaling law that predicts droplet rupture due to cavitation bubble collapse under confinement.

Findings

Identified two regimes: rupture and no-rupture.

Derived a scaling law linking rupture to Weber number and size ratio.

Extended the framework to particle-laden droplets.

Abstract

The interaction between cavitation bubbles and surrounding droplets plays a central role in applications such as surface cleaning, ultrasonic emulsification, and therapeutic delivery. These processes depend on bubble-driven microjets that drive the deformation and breakup of the droplets, which are significantly influenced by geometric confinements. Here, we investigate the hydrodynamic interaction between cavitation bubbles and oil droplets within a thin water layer considering the coupling confinements of a free surface and a rigid wall. We reveal two distinct regimes of droplet response to cavitation bubble collapse: the rupture regime, where oil droplets fragment into smaller droplets, and the no-rupture regime, where the droplet remains intact. By deriving a non-dimensional Kelvin impulse to represent the momentum of the bubble-induced jet, we establish a scaling law that correlates the criterion for droplet rupture to a characteristic Weber number and the bubble-to-droplet size ratio for the first time. This framework delineates the rupture boundary and even extends to predict the rupture of particle-laden droplets driven by cavitation bubbles. Our findings reveal the hydrodynamic principles underlying the cavitation bubble-driven droplet rupture and provide predictive criteria for controlling performance in engineering and biomedical systems involving cavitation bubble dynamics.