Understanding cavity dynamics near deformable oil drop via numerical simulations☆

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 (β) and the stand-off parameter (γ) on cavity-droplet dynamics have been investigated. The influence of these parameters on cavity jet velocity (Umax) and energy dissipation rate (ε) was evaluated. Cavity jet velocity (Umax) 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 β = 2.5(γ = 0.7) and β = 5(γ = 1.2). The energy dissipation rate for cavity-oil droplet interaction is of the order 108 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.