Numerical investigation of electrostatically enhanced coalescence of two drops in a flow field

When an electric field is applied to an emulsion where a conductive fluid is dispersed in an insulating fluid, attractive forces will arise between the drops due to polarization. The drops then tend to coalesce more readily than when no electric field is applied. This phenomenon, often denoted electrocoalescence, is employed for instance to enhance the separation of water from oil extracted from offshore wells. In this work, we employ detailed numerical simulations to study the influence of external flow and electric field on the head-on collision between two drops. The incompressible Navier-Stokes equations are solved in both the oil and water phase using the finite-difference method. The droplet interface is captured using the level-set method. This allows for incorporating interfacial forces due to interfacial tension and electric field in a consistent manner. The discontinuities in physical properties and other quantities across the interface are handled using the ghost-fluid method. In this method, the discretization stencils are modified near the interface to take into account the physical jump conditions. To enlighten the physical processes occurring in a separation vessel, we simulate two drops approaching each other in an externally imposed flow field. The influence of fluid properties and the electric field on the coalescence time is investigated.