Numerical Simulation And Study On Mechanism Of Droplet Coalescence Under Electrostatic Fields

Electro-hydro Dynamics is an interdiscipline between Fluid mechanics and Electrodynamics,which studies the interaction of charged fluid and polarized fluid with electric field.In recent years,with the promotion and application of electric fluid dynamics,it has been widely studied and developed in all walks of life,which includes nanotechnology,biotechnology,MEMS,extraction and microgravity research.There are complex flow,heat and mass transfer phenomena in electric fluid mechanics,the study of interface characteristics and internal flow can help to reveal the mass,momentum and energy transfer process between dispersed droplets and continuous phase under electric field.In this paper,the coalescence process of dispersed droplets in continuous liquid is studied by leakage dielectric model,and the important factors affecting the process and efficiency of droplet coalescence are revealed,which provides some basic research data for the application of electrostatic dehydration or demulsification of crude oil.In this paper,the electric force was added the dynamic equation as the source term by the UDF module in the fluent software,and VOF method is used to track the fluid interface.The numerical simulation of the drop coalescence under the coupling of electric field and flow field is carried out based on the PISO algorithm.Firstly,the numerical analysis of the deformation and internal flow of dispersed droplets in another immiscible liquid under the electric field is studied.which includes the effect of electric field intensity on deformation rate of dispersed droplets?Breakup mode of droplet ? the relationship between breakup limit of droplet and weber number?the tensile direction of droplet and the internal circulation direction of droplet.And then the mechanism of the formation of various phenomena of dispersed droplets under electric field is discussed.Secondly,the coalescence process of double droplets are studied by numerical calculation method.based on the deformation principle of single droplet under the electric field.Factors that affecting coalescence include electric field strength,surfacespacing of dispersed phase droplets,particle size ratio of droplet and relative angle of dispersed droplets.At the same time,The force between two droplets is analyzed by theoretical method,and the main factors influencing the coalescence are discussed.Finally,The characteristic length of the droplets(major and minor axis and liquid bridge)were chosen to characterize the coalescence of droplets.The characteric parameters(major and minor axis and liquid bridge)were acquired by image method under different initial distance of droplet,and the influence of operation parameters on the characteristic quantity is analyzed.