Investigation On The Coalescence Of Droplet-Droplets And Droplet-Interface In W/O Emulsion Under High Voltage Electric Field

As an environmental and highly efficient separation technology,Electrostatic dehydration is widely used for oil-water separation in W/O emulsion.The principle is that the droplets coalescence under the high voltage electric field,gravity settlement,and separated from the crude oil.On the micro level,electrostatic coalescence mainly includes droplet polarization deformation,droplet-droplet coalescence and droplet-interfacial coalescence.To study the microcosmic mechanism of electrostatic coalescence in W/O emulsion,this paper gives investigation on the coalescence of droplet-droplet and droplet-interface in W/O emulsion by numerical simulation software COMSOL,which summarized the influence of factors,and could provide a theoretical basis for the investigation on the mechanism of electrostatic dehydration.A simulation model in two immiscible fluids is established with the phase field method,which is used to investigate the law of droplet deformation as well as distribution of flow field,electric field force and interfacial tension under AC electric field.The results show that the droplet deformation curve and electric field force of droplet endpoint curve are similar to that of the electrical waveforms.And the higher the root mean square（RMS）value of the electric field,the larger the deforming extent of the droplet.With increasing electric field intensity and droplet diameter,decreasing interfacial tension and continuous phase viscosity,the droplet deformation increases under half-sinusodial waveform.In addition,the influence of the electric field frequency on the droplet deformation varies with the electric field waveform.In order to investigate the droplet-droplet coalescence behavior,the simulation model in two immiscible fluids is established with the phase field method.The results show that the higher the electric field intensity,the shorter the coalescence time.In contrast,the shorter the intersection angle between droplets,interfacial tension and continuous phase viscosity,the shorter the coalescence time.When the electric field frequency is 20Hz,center distance between droplets is 1.8mm,and the ratio of the center distance to the droplet diameter is 1.505,the droplets coalescence speed faster.Meanwhile,the coalescence effect will be better under DC pulse and half-sinusoidal electric field.Based on the level set method,the simulation model of droplet-interfacial coalescence is established.The results show that with increasing electric field intensity,decreasing interfacial tension and continuous phase viscosity,the volume ratio of second droplet to the initial droplet（V_r）increases under the same simulation condition.With increasing conductivity,V_r increases first and then decreases,and the peak value is 5.49×10^-4S·m^-1.The relevant achievements of this paper provide theoretical basis for further research on the mechanism of W/O emulsion during electrostatic coalescence process,and provide theoretical principle for further development of effective and compact electrostatic coalescence equipment.