Droplet charge-to-mass ratio measurement in an EHD liquid-liquid extraction system

An experimental investigation has been carried out in a rectangular lucite cell equipped with parallel electrode plates along the two sides of the cell. The droplets are formed at a grounded hollow electrode. Distilled water is used as the droplet phase and a viscous mineral oil is used as the continuous phase. Experiments have been conducted at various flow rates of the dispersed phase with quiescent continuous phase; the applied DC voltage is from 0 to 15 kV. Charge acquired on droplets both at the hollow electrode and downstream near the bottom of the cell was observed from hollow electrode current waveforms and by a Faraday-cup through direct sampling, respectively. The results reported from the present investigation, extending from the single discrete droplet regime (at low applied voltage) to the dispersed multidroplet regime (at high applied voltage), indicate that the modified Rayleigh instability model and the Vonnegut and Neubauer model can predict the maximum droplet charge acquired in liquid-liquid systems. The modified Vonnegut model can predict most of the experimental results when the applied electric field is high enough and EHD (electrohydrodynamic) forces become dominant.<>