Control of reactive species in plasma and dynamics of the interface under plasma-liquid interaction

Abstract

For the optimization of atmospheric pressure plasma in various applications, it is essential to understand the generation mechanism of active species and the interaction between plasma and liquid. In this study, we investigated the expansion of the liquid cavity caused by a helium plasma jet and its influence on liquid properties and methods to control important reactive species such as OH, N$O_x$, and $O_3$, through computational simulations and experiments. As a result, we discovered that the electric wind caused by plasma expand the liquid cavity at the plasma-liquid interface and increase the transport of reactive species in the gas phase. Additionally, in the case of liquids with different surface tension and conductivity, we found that the decrease in surface tension deepened the liquid cavity, while the increase in electrical conductivity suppressed the expansion of the liquid cavity. Furthermore, we established conditions under which major reactive species can be selectively generated and maintained by investigating the effects of UV irradiation, gas temperature, oxygen concentration, and flow rate. Through this research, we revealed that the electric wind is an important phenomenon that increases the transport of reactive species and identified the influence of liquid characteristics on plasma and plasma-liquid interface. Moreover, we obtained operating conditions for controlling major reactive species using the developed plasma computational model. This study is expected to enhance the understanding of plasma-liquid interactions, provide control strategies for reactive species, and serve as a fundamental research outcome to enhance the utility of plasma.