Main purpose of the present work is to obtain uniform droplets ranging between 30 and 450 microns through electrohydrodynamic atomization. Flow rate and voltage input have been changed for two different nozzle materials (stainless steel (STS), silica) to examine the variation of the drop size distribution. Also the configuration of the liquid pendant and the drop formation mode were studied through visualization, and the variation of the charge-to-mass ratio of droplets was studied. Finally a model predicting the drop size was proposed based on the drop formation mechanism.
A tentative mode-classification map has been constructed through visualization of the drop formation process. The spindle mode turned out to be the most probable way to obtain fine uniform droplets of the water-based liquid ranging between 30 and 450 microns. With the stainless steel nozzle, the SMD decreases down to a minimum and then increases within the voltage range covering the spindle mode. On the other hand, with the silica nozzle, more uniform and smaller droplets could be obtained at the inception voltage of the spindle mode.
It was experimentally confirmed that the charge-to-mass ratio of droplets smaller than 200 microns is about the half of the Rayleigh limit. The drop size distribution appears the most uniform when the electric repulsive force at the surface is just balanced by the surface tension force. The size of the droplets generated from the liquid meniscus could be predicted based on the principle of the minimum energy dissipation proposed by Grigor’ev et al. (1991), but with further introduction of the physical models for the initial velocity and electric charge of the droplets, electric field strength at the nozzle tip and the liquid-cone angle. The predicted drop sizes agree with the measured data within the accuracy range of ±10%.
