Mode and mechanism of water droplet breakup in oil under high-voltage and high-frequency pulsed electric fields

Abstract

In industrial processes, the application of pulsed electric fields for electrostatic demulsification may cause droplet breakup, reducing demulsification efficiency. In this paper, a comprehensive approach combining microscopic experiment, theoretical derivation, and molecular dynamics simulation, were employed to explore the water droplet breakup in water-in-oil (W/O) under high-voltage and high-frequency pulsed electric fields. The results showed that droplet breakup would occur when the electrostatic tensile stress of the droplet surpassed the additional compressive stress. Three main modes of droplet breakup were observed: breakup at one end, breakup at both ends, and breakup in the middle part. By applying Maxwell stress equation, critical field strengths were derived to predict breakup locations. In the pulsed electric field, the droplets underwent a sequence of stretching, retraction, and eventual breakup. The formation and migration of hydrated ions was of crucial importance in the droplet breakup. A decrease in electrostatic attraction between H2O and an increase in dispersion attraction effect between H2O and C6H14 promoted the droplet breakup. The number of hydrogen bond inside the droplet was reduced, weakening the stability of droplet. The energy of electric field was transformed into the deflection of dipole moment and the velocity of water molecules. The time required for droplet breakup decreased when the pulsed electric field strength increased. The research findings in this paper uncovered the mechanism behind the breakup of water droplets in pulsed electric fields, and offered theoretical guidance for optimizing demulsification processes.