LAUSR

Abstract The electrocoalescence of aqueous drops in an insulating oil is the fundamental process in the dehydration of emulsions of water in insulating oils, such as crude oils. The great difference in the conductivity of the aqueous droplets and the oil used as the suspending medium suggests that the conductivity of the oil medium should not affect the coalescence process. In this work, contrary to this expectation, we show a very strong dependence of the conductivity of the insulating oil on the mode of droplet coalescence. Experiments are reported using silicone oils, vegetable oils, and hydrocarbons, in the anchored drop setup that also facilitates the use of low viscosity oils. Our study indicates that the droplet undergoes cone-cone mode of interaction at low conductivities of the oil medium. On the other hand, when the conductivity of the oil is increased, the cone-dimple mode of coalescence is observed when the viscosity of the oil phase is higher, while a cone-spray-dimple mode is observed when oils of low viscosity are used.