Shear flow of an emulsion of drops less conductive than the suspending fluid immersed in an electric field by numerical simulation

The application of an electric field modifies the microstructure and properties of an emulsion. Under shear, the response of the system is dictated by the competition between electrical and hydrodynamic forces. Direct numerical simulation is used to examine the response for an emulsion composed of drops less conductive than the suspending fluid. The presence of an electric field results in an attractive force between the drops in the direction parallel to the electric field. If no shear is present, the drops aggregate in chains parallel to the electric field and the microstructure becomes highly anisotropic. The immersion of the emulsion in a simple shear leads to the tilting and break-up of the chains of drops. The effective viscosity exhibits shear-thinning properties associated with the changes in the microstructure. The variation in the viscosity of the drops also impacts the properties of these systems: an increase in the drop viscosity results in an increase in the emulsion effective viscosity. The electric field also enhances the elastic properties, which depend on the deformation of the drops and any difference in the viscosity between the fluids. The variation in the viscosity ratio translates into a modulation of the normal stress differences. At low shear rates, the deformation of the drops is mostly dictated by the electric stresses. An increase in the viscosity ratio results in the enhancement of the drop deformation, which causes an increase in the first normal stress difference. At high shear rates, the deformation of the drops depends more on the viscous forces and less on the electric field. In this regime, an increase in the drop viscosity results in more rigid drops, which decreases the first normal stress difference.