Investigation of the role of viscosity on electrocoalescence of water droplets in oil

The sedimentation velocity of water droplets in oil increases proportionally to the square of the droplets diameter. It is therefore beneficial for the separation of water from oil to increase the droplet size by enhancing the coalescence process. Electric fields are used for this purpose in order to separate stable water-in-oil emulsion. Field-induced charges on the water droplets will cause adjacent droplets to align with the field, attract each other and ultimately coalesce. The efficiency of electrically induced coalescence is strongly dependent on the oil characteristics. In the present study experiments are performed to observe the behavior of a droplet falling onto a stationary one at different oil viscosity. The droplet is exposed to an electric field of different magnitude parallel to the direction of the droplet motion. Experimental observations are compared with numerical prediction of the droplet kinematics, and the contribution of the forces acting on the droplets and their dependency on viscosity is discussed in detail.