Polarity effect on the electrohydrodynamic (EHD) spray of water

Abstract

This paper presents the effects of polarity on the electrohydrodynamic (EHD) spray of water (deionized and tap water) in air and pure CO2 environments. Its influence in the interaction of the EHD spray and corona discharges was experimentally measured and analyzed. In contrast to the various spray patterns observed under positive polarity, negative polarity induced only two modes (dripping and spindle) under the typical conditions used in this study. Mapping of electrospray modes is presented in conjunction with current–voltage characteristics, discharge and spray images obtained with ICCD and high-speed camera. We also first report the intermittent multi-jet mode in water in pure CO2. The essential differences in the spindle mode were the shape and elongation direction of the water filaments according to the negative or positive polarity. The different spray patterns in the spindle mode seemed to be associated with the movement of ion species in water. From the combined analysis of the corona discharges, one may conclude that the different properties of the coronas were associated with the spray patterns in both air and pure CO2. Typical onset streamers in air under positive polarity had minimal influence on the spray mode because they were found to be separated in time and space from the water meniscus. In contrast to the stable glow under positive polarity, many current pulses (Trichel pulse) were observed in the negative EHD spray.