Understanding cavity dynamics near deformable oil drop via numerical simulations

Abstract

Cavitation is increasingly being used for producing liquid–liquid emulsions. Cavity collapse generates microscale high-speed jets, which play a crucial role in cavitation-driven emulsification. It is thus essential to investigate the interaction of cavity and droplet to improve the understanding of the cavitation-driven emulsification process. In this study, we have numerically investigated the interaction of a single cavity-droplet pair dispersed in a water medium mimicking the scenario occurring inside a hydrodynamic cavitation-based fluidic device. A direct numerical simulation utilizing the multi-fluid, volume of fluid (VOF) method has been used for simulating different scenarios of cavity droplet interactions. The effect of the droplet-cavity size ratio ($\beta$) and the stand-off parameter ($\gamma )$ on cavity-droplet dynamics have been investigated. The influence of these parameters on cavity jet velocity $\left(U_{\max }\right)$ and energy dissipation rate $\left(\epsilon \right)$ was evaluated. Cavity jet velocity ($U_{\max }$) increases at first, then decreases with the stand-off parameter whereas it increases and becomes almost constant for the size ratio. The maximum cavity jet velocity in the present work is obtained for the case $\beta =2.5(\gamma =0.7)$ and $\beta =5(\gamma =1.2)$. The energy dissipation rate for cavity-oil droplet interaction is of the order ${10}^8$ m²/s³, irrespective of the stand-off parameter and size ratio for a given driving force. The results presented in this work improve the current fundamental understanding of cavity–drop interactions and provide a useful basis for developing cavitation-induced droplet breakage models for predicting droplet size distributions, enabling enhanced applications of cavitation for emulsification in the chemical industries.