Harmonic spraying of conducting liquids employing AC-DC electric fields

This paper reports the results of the work carried out to investigate the breakup process of charged conducting liquid jet under the influence of an AC field superimposed onto a DC field. The main aim of this paper is to optimize the spraying parameters and to generate uniform droplets of highly conducting liquid in a controlled fashion by varying the strength and the frequency of the applied AC field. The electric field at the tip of a blunt needle facing a ground electrode was examined using a finite-element modeling technique. Three types of ground electrode configurations were investigated. A mathematical model for the electrostatic force on the leading edge of the droplet as a function of the liquid flowrate, the applied voltage, and distance between the capillary tip and the ground electrode has been developed. The breakup and droplet formation processes were investigated using a telemicroscopic lens and charge-coupled device (CCD) camera. The video data was processed using frame grabber software installed on a PC. The digital images were then analyzed utilizing image analysis software to give information on the breakup process and the size of droplets. A frequency range was identified where the formation of the droplets was synchronized with the applied AC field frequency. The effects of liquid flowrate on the synchronous bands were examined. The experimental results showed the dependency of the droplets size and the emission frequency on the applied AC frequency.