Investigation On The Transient Response Mechanisms Of Droplet Interface To Electric Field

The droplet deformation and breakup process are of great importance to the electrocoalescence of droplet in the chemical flooding water-in-oil?W/O?emulsion.Therefore,the key to solve the problem is to explore the transient response of droplet interface to the electric field from the aspect of interface dynamics,which is helpful to enhance the droplet electrocoalescence.It is also the key technical problem which needs to be solved in engineering practice.By combining theoretical analysis with micro-scale experiments,the droplet interface motion model under the electric field is established in this paper,the mechanisms of transient response of droplet interface in the process of droplet deformation and before droplet breakup are obtained.Also,the influences of electric field parameters,physicochemical properties of fluids and the interfacial properties on interfacial transient response are discussed in detail.The results are very important to develop the electrocoalescence theory and to the research and design of high-efficiency electrodehydrator.The main research contents and conclusions are as follows:Considering the electric stress,pressure resistance,capillary pressure and additional pressure,the transient response models of the droplet interface to the direct current?DC?electric field and the sinusoidal alternating current?AC?electric field are established,and the calculation results are in agreement with the experimental values.Based on the coupled equations of the interfacial motion model and the interfacial rheological constitutive equation,the theoretical description of the viscoelastic interfacial motion of droplet under the electric field is realized.The establishment of the model lays a theoretical foundation for exploring the dynamic response laws of viscoelastic interface to electric field.The characteristics of transient response of pure interface and viscoelastic interface to DC electric field are studied theoretically and experimentally.Based on the transient response model of droplet interface,the interfacial dynamic response time,interfacial oscillation modes,the amplitude,the oscillatory period and the damping coefficient are explored in detail.The relationship between these characteristics and the electric capillary number Ca,Ohnesorge number Oh,C_m^*,the interfacial elastic coefficient T₁ and the interfacial viscosity coefficient T₂ are interpreted.And the mechanisms of the interfacial motion under the DC electric field is obtained.The interfacial response modes and the corresponding C_m^*-Ca-Oh conditions are found,as well as transition rules between different modes.Furthermore,the influence of the interfacial viscoelasticity on the interface motion is revealed.It is found that through the reasonable control of the Ca number,Oh number and the interfacial properties,the excessive oscillations of droplet interface can be effectively controlled.As a result,the transient response of pure interface to the DC electric field could be optimized.The steady-state oscillation of the interface to the sinusoidal AC electric field is explored by the stress analysis,as well as the the influences of Ca,Oh,C_m^*,the dimensionless electric frequency?^*and interfacial viscoelasticity on the oscillatory amplitude and phase difference.The results show that:since the interface is subjected to the alternating electric pressure in the AC electric field,the synergistic effects of the dimensionless electric frequency?^*,Oh,C_m^*and interfacial viscoelasticity significantly change the inertia force and viscous stress on the droplet interface during its oscillation.Consequently,the phase difference corresponding to the steady-state oscillation of the interface is also changed,which has a significant impact on the amplitude-frequency characteristic of the interfacial oscillation.The transient response of the droplet interface before its breakup is discussed,and the influences of Ca,Oh,the dimensionless electric frequency?^*and interfacial viscoelasticity are also explored.The study found that due to the change of stresses before droplet breakup,the droplet deformation process can be divided into three stages:the rapid increase stage,slow increase stage and rapid increase stage again.The time interval of the second stage plays an important role in the controlling of droplet breakup process.With the decrease of Ca and the increase of Oh,the electric field frequency and the interfacial viscoelasticity,the time interval of the second stage increases,and the overall deformation rate decreases before the droplet breakup.Therefore,the droplet breakup process could be postponed by reducing Ca and increasing Oh and electric field frequency,which can be achieved by the reasonable control of the droplet and the continuous phase properties,the interfacial properties and the electric field parameters.