Scaling analysis of droplet forces in electrocoalescence: effect of frequency and waveform on dehydration efficiency

Millisecond-scale electric fields and minute-to-hour sedimentation times complicate the direct simulation of electrocoalescence. A scale analysis of the electrocoalescence process was performed, leading to the conclusion that the dielectrophoretic (DEP) force is the primary force involved. Since the dielectrophoretic force does not change direction during electrocoalescence and the electric field timescale is much smaller than droplet sedimentation, an average DEP force is proposed for analyzing the electrocoalescence process. This uncouples the dynamics of the electric field and sedimentation, simplifying the understanding of the process.As the DEP force drives droplets toward the electrodes, droplet-to-electrode coalescence becomes an important mechanism. The frequency effect on electrocoalescence was examined in light of droplet oscillation. A non-dimensional number, similar to the Deborah number, was defined for the electrocoalescence process. It was demonstrated that high frequencies enhance electrocoalescence by protecting large droplets from breaking. The theoretical derivations were successfully applied to interpret batch electrocoalescence data under various waveforms, voltages, and frequencies.