Forces and movement of water droplets in oil caused by applied electric field

Abstract

The effect of applying an electric field to an emulsion of water and oil is to induce attractive forces and enhance the coalescence of adjacent water droplets. In the oil industry, it is common to utilize this process, called electrocoalescense, to enhance oil-water separation by enlarging the water droplets. The work presented here describes the forces influencing the kinematics of droplets, with radius around 0.5 mm, exposed to an electric field when falling in stagnant oil. Different mathematical simulation models are tested and the results are compared with experiments made with two falling droplets exposed to an electric field perpendicular to the direction of their motion. The trajectory of the water droplets has been optically determined using a high speed digital camera. The results show that when the droplets are more than one droplet radius apart, the electric forces can be accurately determined using the dipole approximation. At smaller distances, numerical field calculation techniques and the effect of film thinning need to be considered.