Study On Electrohydrodynamic Atomization Process And Atomization Characteristics With Capillary

Electrohydrodynamic atomization can obtain uniform micro-droplets,and different spray modes and droplets with different particle diameters can be obtained under different operating parameters.Therefore,electrohydrodynamic atomization was widely used in inkjet printing,spraying,space propellers and other fields.In the process of electrohydrodynamic atomization,the force state of droplets/jets was complex,and there was a difficult relationship between the various forces.And it was currently difficult to obtain a specific physical model to describe.In this paper,the capillary electrohydrodynamic atomization process and atomization characteristics were studied in detail using experimental methods.The force and periodic characteristics of the droplets under different spray modes and the droplet/jet characteristics of the electrohydrodynamic atomization in the micro-dripping/spindle mode were discussed.The details are as follows:Firstly,a capillary electrohydrodynamic atomization experimental device was designed and built.Using the high-speed digital camera technology,the anhydrous ethanol single capillary electrohydrodynamic atomization processes were recorded.Typical spray modes such as dripping,micro-dripping,spindle,multi-spindle,cone-jet,precession-jet and multi-jet were obtained.The force of droplets of single capillary ethanol under different spray modes was analyzed.The relationship between the droplet trajectories and the force of droplets were also discussed.The research results show that in the process of electrohydrodynamic atomization,the droplets were mainly subjected to various force fields such as gravity,Coulomb force,surface tension,electric field force and deformation force.When the voltage was low,gravity and surface tension play a leading role in the electrohydrodynamic atomization process,with the increase of the voltage,the electric field force gradually becomes the dominant factor affecting the atomization process.This mutual conversion between the multiple force fields results in different trajectories of the jets（droplets）and ultimately presents different modes of electrohydrodynamic atomization.Secondly,using high-speed digital camera technology,the electrohydrodynamic atomization process of single ethanol and deionized water with single and double capillary tubes were recorded and the corresponding atomization mode were obtained.The periodic characteristics of droplets during the electrohydrodynamic atomization of anhydrous ethanol and deionized water were investigated.Electric Bond number B_E and dimensionless flowQ₀Qwere used as characteristic parameters of the electrohydrodynamic atomization mode.The distribution pattern of anhydrous ethanol single capillary spray mode was obtained.The results showed that the droplets were mainly subjected to gravity and surface tension in the initial stage of atomization.As the voltage increases,the electric field force gradually becomes the dominant factor affecting the separation of the droplets,within the entire atomization range,with the increase of the electric Bond number B_E,the periodic frequency of the double-capillaries droplets showed an increasing trend,and there was a period of sudden increase of the periodic frequency in the respective atomized regions.In the sudden increase stage,the periodic frequency increased fast.Afterwards,with the increase of the electric Bond number B_E,the periodic frequency growth slowed down again.Third,the Electric Bond number B_E and the dimensionless flow q were used to study the characteristics of droplet cycle characteristics in the dripping/spindle mode,the ratio of the long/short axis of the droplet to the outer diameter of the capillary in the spindle mode,and the droplet equivalent diameter conversion characteristics in the spindle mode.The results show that there was an area where the flow has no effect on the periodic frequency during the sudden increase in the periodic frequency.The values of D_S/D and L_S/D show a linear relationship with the increase of dimensionless flow q,and under the same dimensionless flow q,the change trend of the electric Bond number B_E was exactly the opposite in D_S/D and L_S/D.In the equivalent diameter transformation characteristic,the equivalent diameter d_d exhibits a certain linear relationship with the dimensionless flow q.