Study On Dynamic Characteristics Of Toroidal Droplets On A Solid Substrate Under An Electric Field

The toroidal structure has a wide range of application values in food processing,industrial manufacturing,biomedicine,3D printing technology and other fields.However,due to Rayleigh-Plateau instability,the shape of the toroidal structure becomes difficult to maintain,which affects the engineering application of this toroidal structure.This subject is based on the key scientific problems of 3D printing toroidal structure technology on a solid substrate under the external electric field force,and studies the flow stability and nonlinear evolution of toroidal droplets deposited on a solid substrate under the electric field force from the physical mechanism.It has important scientific research value in revealing the ringforming mechanism of the toroidal droplets,the breaking mechanism under the external electric field force.In terms of theoretical analysis,the correlation between the formation time and breaking time of the toroidal droplets on a solid substrate was derived,and the relationship between the volume of the toroidal droplets,the aspect ratio,and the contact angle was analyzed.When the width a0 and aspect ratio R0/a0 of the toroidal droplet are determined,the volume of the toroidal droplets increases with the increase of θ.Under certain a0 and θ,the volume of the toroidal droplets is proportional to the aspect ratio,and the larger the contact angle,the greater the slope.The fracture mechanism of the toroidal droplets under an electric field was analyzed from the perspective of the force acting on the toroidal droplets.The toroidal droplets are subjected to electrical stress,gravity,shear stress,friction,etc.When the electrical stress reaches a certain value,the toroidal droplets will expand.In terms of numerical simulations,the fluid flow module in COMSOL Multiphysics is used to simulate the experiment.The Level-set method is used to capture the interface between the fluid and air,and a three-dimensional transient model is used to study the evolution process of droplets on a solid substrate.Numerical simulations of the effects of aspect ratio,surface tension,viscosity,and final contact angle between liquid and solid substrate on the evolution of the toroidal droplets.The numerical results indicate that the above parameters will change the time from the initial state to the final state,and surface tension play a promoting role in the evolution of the toroidal droplets,while viscosity plays a restraining role.In the experimental research,a set of devices that can make toroidal droplets on a solid substrate and apply an electric field was built.Using different mass fractions of PVA,NaCl,and Tween 20 for experiments.Analyzing the toroidal droplets with different initial aspect ratios subjected to voltage values of 0 V,3000 V,and 6000 V.The aspect ratio corresponding to the mode with the largest growth rate is fitted with a positive proportion function,respectively.The larger the voltage,the greater the slope.The effects of different conductivity,surface tension and viscosity of the toroidal droplets under 4000 V voltage and the same aspect ratio were discussed.The influence of voltage value on toroidal droplets at the same aspect ratio was studied.The experimental results show that the conductivity and surface tension promote the split of the toroidal droplets,while the viscosity inhibits the split of the toroidal droplets.The greater the electric field force,the more obvious the expansion,and the more spherical droplets tend to break.