Electrohydrodynamic breakup of a leaky dielectric drop in pressure-driven flow

We numerically investigate the breakup dynamics of a leaky dielectric droplet migrating through a confined microchannel under the combined influence of Poiseuille flow and a transverse electric field. The multiphase flow problem has been modeled using a coupled Navier–Stokes equation and phase-field method. Deformation and breakup behavior of the drop have been studied extensively for wide ranges of electrical capillary number (Cae), capillary number (Ca), electrical conductivity ratio (R), and electrical permittivity ratio (S). Five distinct breakup modes are observed: equatorial breakup (EB), equatorial polar breakup (EPB), polar breakup (PB), oblate fish breakup (OFB), and oblate breakup unstable (OBU). The novel EB regime is characterized by the bending of the prolate-deforming droplet (R > S) and its subsequent disintegration into identical twins exactly at the channel centerline as a collective consequence of higher viscous force (high Ca) and strong electric field (high Cae). The EPB mode demonstrates characteristics of both EB and PB regimes at high R and moderate to low S. For an oblate deforming droplet (S > R), at large Cae, we identify an intriguing OFB mode, marked by a wavy interfacial morphology mimicking fish motion, which eventually breaks from crest and trough locations. Further increase in Cae accelerates this breakup process to such an extent that it transforms to an entirely unstable disintegration mode (OBU). Finally, the regime diagram predicted by our study reveals how the interplay of pertinent forces and electrical properties governs droplet breakup, offering insight and useful design criteria for microfluidic applications.