Electro-coalescence of droplets in time-periodic electric fields: A numerical investigation

The electro-coalescence, which is a phenomenon of coalescence in the presence of electric field of two equal-sized droplets with constant surface tension at the droplet and medium interface, has been investigated based on the phase-field model to track the evolution of the droplet interfaces. The coalescence efficiency has been quantified by analyzing the growth rate of the bridge radius after the droplet tips merge, as well as the total coalescence time, defined as the sum of the approach and fusion times. The results demonstrate that the coalescence efficiency highly depends on the type of electric field applied. In this study, the behavior of coalescence under direct current (DC) and alternating current (AC) fields for high capillary numbers has been explored. Furthermore, the restoration of the spherical droplet shape under AC and DC fields at high capillary numbers has been examined. The coalescence characteristics of various waveforms with the same root-mean-square electric field strength, including AC, half-cosine, and DC square waves, at both low and high frequencies have been compared. Special emphasis has been placed on analyzing how the frequency affects electro-coalescence and the sensitivity of the coalescence happens time to frequency variations for time-periodic electric fields.