Numerical prediction of the electrical waveform effect on electrocoalescence kinetic

Abstract

The effect of external electric field characteristics on the binary water droplet coalescence in stagnant oil has been studied using Computational Fluid Dynamics (CFD) simulations. Volume of Fluid (VOF) approach is applied as a multiphase model, in which the hydrodynamic equations consisting of Navier–Stokes and interface tracking equations are solved using finite volume discretization scheme. Dipole-induced-dipole (DID) model is utilized to calculate the electrostatic force on water droplets. Different types of electrical waveforms have been implemented using appropriate potential functions. The studied electrical voltages are sine, triangle, sawtooth, pulsed DC, and bipolar square waveforms. The predicted kinetic for electrocoalescence is in good agreement with the experimental data of the literature. The results demonstrated that a bipolar square wave provided the most efficient waveform, while sine and pulsed DC voltages gave lower efficiencies due to the time variation and off-time intervals, respectively. Triangle and sawtooth waveforms produced the least efficient waveforms. In addition, the effect of frequency has been studied for the aforesaid electrical waveforms in the adopted binary drop system. No significant differences have been proved in the approaching time of the drops from the studied frequencies. The results revealed that the electric fields with higher value of root mean squares (RMS) result in more efficient electrocoalescences. Furthermore, it was manifested that the higher voltage amplitude in every waveform improves this phenomenon.