Formation of mono-dispersed droplets with electric periodic dripping regime in electrohydrodynamic (EHD) atomization

Abstract The formation of controllable size and dripping frequency in ectrohydrodynamic (EHD) atomization with electric periodic dripping regime are of much interest and importance because of significant and wide applications, such as micro-encapsulation and ink-printing. In present study, the experimental and theoretical works were carried out to explore droplets formation in periodic dripping regime in presence of an electric field. The dimensionless electric charge carried by each droplet produced is smaller than the 50 % of critical value of the Rayleigh limit, where charge-to-mass ratio of droplets was obtained through the deflection distance in the presence of an electric field. The droplet in electric periodic dripping regime usually undergoes oscillating deformation, and finally forms a spherical droplet below the tip no more than ten times out diameter of tube. The droplets size tens of microns to one hundreds of microns decreases with an increase in applied potential. In the electric dripping mode, droplets size is independent of flow rate and affected by flow rate due to adsorption of surface active species in micro-dripping. The simplified model to predict droplets size was derived from the balance of electric, surface tension and gravity forces. The droplets size calculated is good agreement with the experiments. Meanwhile, the dripping frequency of droplets with rang of a few to several hundred Hz obtained from time-resolved images is highly dependent of liquid flow rate and electric potential. The largest dripping frequency was predicted and in reasonable agreement with the experimental results. In electric periodic dripping regime drop-on-demand droplets in size and dripping frequency further our understanding on the formation of identical droplets and are beneficial to many practical applications.