Electrocoalescence dynamics of two unequal-sized droplets

The present study investigates the electrocoalescence dynamics of two unequal-sized water droplets surrounded by a different fluid (typically considered oil). Finite element method-based level-set formalism has been adopted to solve the governing transport equations for a two-dimensional framework, and the accuracy of the solver is ascertained by validating with previously reported experimental results. The study extensively explores the characteristics of the droplet-to-droplet coalescence phenomenon, which is governed by key determinants like electric field strength , diameter ratio of the coalescing droplets, and viscosity of the fluids. It reveals that the electric field application shifts the coalescence regime from complete to partial beyond a limiting field strength for a corresponding diameter ratio. For a larger diameter ratio, the electric field strength required to get partial coalescence is relatively smaller than that needed for a smaller diameter ratio. In the context of partial coalescence, increasing electric field generates larger satellite droplets. With significantly higher electric field strength application, the satellite droplet goes under the second stage pinch-off phenomenon without coalescence. The partial coalescence gets suppressed with the increase in viscosity of the surrounding fluid; however, with the application of a larger voltage, partial coalescence can be achieved even for higher viscous fluid, and the same becomes more susceptible at a higher diameter ratio of the droplets. Finally, it is also established with an extensive comparison of how the present work is fundamentally remarkable and holds the utmost significance in the community of droplet dynamics research.

Automated summary

The present study investigates the electrocoalescence dynamics of two unequal-sized water droplets surrounded by oil. The study uses the finite element method-based level-set formalism to solve the governing transport equations and validates the solver accuracy with experimental results. The key determinants of droplet-to-droplet coalescence phenomenon are electric field strength, diameter ratio of the droplets, and viscosity of the fluids. The study reveals that higher electric field strength leads to partial coalescence and the required field strength is smaller for larger diameter ratios. Higher viscosity suppresses partial coalescence, but with larger voltage, partial coalescence can be achieved even for higher viscous fluid.