Study On Behavior Of Dispersed Phase Droplets Under The Influnence Of An Electric Field

In the oil-field industries, petroleum demulsification is an extremely important process. Among many demulsification methods, electrical demulsification helps tiny droplets coalesce into larger ones and then settle out. From the viewpoints of energy efficiency and non-pollution, electrical demulsification is the best method to separate water droplets from water-in-oil emulsion and widely used in oil-field industries. However, due to the complexities of the hydrodynamics and electrostatics interaction in the droplets coalescence process, most of pioneering works focus on the coalescence mechanism at a macro level, the present literatures are lack of systematic investigation on the fundamental study of the droplets coalescence from the micro-perspective. Therefore, in order to increase the understanding the knowledge of coalescence mechanism at a microscopic level, in this paper through coupling with hydrodynamics and electrostatics, a phase method has been adopted to predict the deformation, break-up and coalescence behavior of dispersed water droplets under the influence of an electric field.The phase field method was used to predict deformation, breakup and coalescence behavior of dispersed phase droplets under the influence of a uniform electric field. The distribution of charge density and electric field force on the droplet surface, as well as the distribution of electric field and flow field were studied from the micro-perspective, and the micro-droplet deformation, breakup and coalescence mechanism was established. The deformation and coalescence behavior of droplets is affected by many factors: the simulation results showed that increasing electric field intensity, droplet diameter, initial surface charge density, while decreasing oil viscity and interfacial tension could cause larger degree of droplet deformation. The simulation results also revealed that increasing the electric field strength, initial velocity, initial surface charge density, interfacial tension or droplet diameter accelerates coalescence rate, while increasing droplet distance or oil viscosity prolongs coalescence time.The phase field method was adopted for predicting deformation and coalescence behavior of charged droplets under the influence of a uniform electric field. Due to the influence of initial surface charge density, the charged droplet occured obvious electrophoresis. When a neutral droplet and a charged droplet occured coalescence under the influence of a uniform electric field, the charged droplet moved faster than the neutral one. In addition, increasing initial surface charge density could cause larger velocity difference of the neutral droplet and the charged one.The phase field method was also used to predict deformation and coalescence behavior of dispersed phase droplets under the influence of an alternating electric field. In the presence of the applied electric field, the deformation of droplet was periodic, and the frequency of droplet deformation was twice of alternating electric field frequency. The periodic oscillating deformation of droplet is affected by many factors:the simulation results showed that increasing electric field intensity and droplet diameter, while decreasing electric field frequency, oil viscity and interfacial tension could cause larger degree and oscillating amplitude of droplet deformation. In the presence of the alternating electric field, the electric field frequency played a significant role in the droplets coalescence, decreasing electric field frequency could cause larger degree and oscillating amplitude of droplet deformation, which could accelerate coalescence rate of two droplets, and the cause less coalescence time.In this paper, the behavior of dispersed water droplets under the influence of an electric field were investigated from the micro-perspective, and some theories have been obtained. The above study will provide a theoretical foundation for the electric demulsification application.