Study On Rupture Mechanism Of Water Droplet In Oil Under DC Electric Field

In petrochemical industry,high electric field can promote the coalescence of droplets in oil,leading to demulsification of stable emulsion.When the applied electric field intensity is too high,the droplets will rupture into small droplets.Water droplets coalescence or rupture behavior is mainly affected by electric field parameters and physical properties.Based on microscopic experiments and theoretical analysis,this paper systematically studied the droplet fracture behavior under DC electric field and dynamics mechanism of droplet,which is of great significance for electrostatic coalescence theory and industrial application.The main research contents and conclusions are as follows:The evolution process of droplet fracture under DC electric field was studied.The critical capillary number of droplet rupture is experimentally proved to be 0.2.There are three consecutive processes in the fracture response process(namely,stretch process,necking process and rupture process).Based on different characteristics of droplet rupture,three deformation forms are observed in the stretch process(namely,conical deformation,ellipsoidal deformation and cylindrical deformation)and three rupture forms in the rupture process as well(namely,conical jet,lob&conical jet and filamentous rupture.)This paper systematically studied the effect of electric capillary number,viscosity ratio,conductivity ratio and surfactant concentration on droplet rupture behavior.Four kinds of typical rupture forms were captured in the experiment,that is,Conical-Conical Rupture,Ellipsoidal-Lob&Conical Rupture,Cylindrical-Filamentous Rupture and Ellipsoidal-Filamentous Rupture.The rupture forms phase diagram indicates that the main factors determining droplet rupture forms are electric capillary number and the surfactant concentration.What's more,this paper analyzes the relationships of the rupture forms and capillary number,as well as rupture forms and surfactant concentration.The evolution law of dynamic response parameters(tensile speed and stretch time etc)in different rupture forms was studied.The speed of long axis endpoints differs with rupture forms.From high to low,there are Cylindrical-Filamentous Rupture,Ellipsoidal-Filamentous Rupture,Ellipsoidal-Lob&Conical Rupture and Conical-Conical Rupture.The main factors of droplet stretch time are electric capillary number and the surfactant concentration.Within the scope of the experiment,the minimum of water droplet stretch time is about 10 ms.Pulse electric field that hinders the droplet rupture behavior is preliminarily designed based on the minimum required time for droplet rupture.Based on the stress-strain theory this paper explains the dynamics mechanism of droplet rupture under DC electric field.The droplet fracture forms were quantitatively classified by employing the characteristic parameter k.The droplet rupture form is Conical-Conical when k<300 N/m~2.The droplet rupture form is Ellipsoidal-Lob&Conical when 300 N/m~2<k<1500N/m~2 and Ca<0.35.The droplet rupture form is Ellipsoidal-Filamentous when 300N/m~2<k<1500 N/m~2 and Ca>0.35.The droplet rupture form is Cylindrical-Filamentous when k>1500 N/m~2.