Numerical Study on Jet and Stretch Behaviors of an Impingement Leaky-Dielectric Droplet Under Electric Field

Abstract

The droplet breakup and ejection after impact under electric fields has attracted increasing attention in industrial applications, such as spray cooling, 3D printing, anti-icing of powerlines, etc. We numerically investigated the leaky-dielectric droplet impact on the hydrophilic surface in perfect dielectric surrounding under vertical electric field with OpenFOAM. The coupled volume of fluid (VOF) and leaky dielectric model have been used to solve two-phase electrohydrodynamic (EHD) problems. Impact behaviors are most strongly influenced by the electric capillary number, dielectric permittivity and electrical conductivity. Four impact modes were registered: no-stretch-no-jet, single-droplet split, stretch-no-jet and stretch-jet. The mechanism of the four impingement modes is explained through the relationship between normal electric stress, tangential electric stress and charge relaxation. The stronger distribution of normal electric stress near the cylindrical tip of the droplet leads to a stretching behavior. Then, the stretched filament must be sustained by tangential electric stresses. The surface charge distribution influences the electric stresses, which depend on charge relaxation, charge convection and tip curvature. Furthermore, the relationship between the electric capillary number, dielectric permittivity, electrical conductivity and the breakup modes was obtained. These findings could facilitate the design of electrospray cooling, deicing for power transmission lines, and 3D printing.

Keywords: Breakup, ejection, electrohydrodynamic effects, drops