Harmonic spraying of conducting liquids employing AC-DC electric fields

This paper reports the results of the work carried out to investigate the break-up process of charged conducting liquid jet under the influence of an AC field superimposed onto a DC. The main aim of this study was to optimise 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 modelling technique. Three types of ground electrode configuration were investigated. A mathematical model for the electrostatic force on the leading edge of the droplet as a function of the liquid flow rate, the applied voltage, and distance between the capillary tip and the ground electrode has been developed. The break-up and droplet formation processes were investigated using a telemicroscopic lens and CCD camera. The video data was processed using frame grabber software installed on a PC. The digital images were then analysed utilising image analysis software to give information on the break up process and the size of droplets. A frequency range was identified where the formation of the droplets was synchronised with the applied AC field frequency. The effects of liquid flow rate on the synchronous bands was examined. The experimental results showed the dependency of the droplets size and the emission frequency on the applied AC frequency