Study of the electrospraying of water in combination with atmospheric pressure corona discharge

This thesis explores the effect of electrospraying of water in combination with atmospheric positive DC corona discharge in air. The electrospraying effect of liquids has been a subject of research since the beginning of the last century and found importance in many diverse fields. Recently, one of the potential uses of water electrospray, especially large flow rate modes, has become a decontamination of water from organic and microbial pollutants. The presence of an electrical discharge generating non-thermal plasma in the spraying zone allows for very efficient mass transfer of plasma-generated species into water. We used a point-to-plane geometry of electrodes with a various types of hollow syringe needle anodes opposite to the metal mesh cathode. We employed the iCCD and high-speed (HS) camera visualization techniques, oscilloscopic discharge current measurements, total average current measurements, and optical emission spectroscopy (OES). These were used in order to visualize the formation of water jets (filaments) in various electrospraying modes and to investigate the corona discharge behavior during this process. The following modes of electrospraying typical for water were observed: dripping mode and spindle modes for low and medium flow rates, and simple jet modes for high flow rates. The geometry of the HV stressed electrodes had a significant influence on the electrospraying process. A nozzle was more suitable for stable electrospray generation and a needle for intense discharge generation. We observed different electrospraying and corona discharge behavior in dependence on the water flow rate and water conductivity. Generally, pointy, elongated, and fast spreading water filaments were observed for lower water conductivity; in contrast to rounder, broader, and shorter quickly disintegrating filaments for higher conductivity. In addition, with increasing conductivity, the breakdown voltage for corona-to-spark transition was decreasing. For a limited range of voltages, the frequency of intermittent water filament generation in spindle modes agreed well with the frequency of the measured streamer current pulses. After each streamer, a positive glow corona discharge was established on the water filament tip and it propagated from the stressed electrode along with the water filament elongation. These results show a reciprocal character of the intermittent electrospraying of water and the presence of corona discharge, where both the electrospray and the discharge affect each other. (author)