Comparison of the Transportation of Reactive Species from He and Ar Atmospheric-Pressure Plasma Jets to Aqueous Solutions

In this study, the transportation of reactive species from argon (Ar) and helium (He) atmospheric-pressure plasma jets (APPJs) to water is comparatively investigated using two-dimensional (2D) fluid models. For the same gas flow rate and reactive species concentration at the jet orifice, the transportation efficiency of the Ar APPJ is found to be higher than that of the He APPJ by 3.7 times. This is primarily attributed to the difference in the gas flow between the Ar and He APPJs. Ar has a higher molecular weight than air, which allows the reactive species in the Ar gas flow to sufficiently contact the water surface. He is much lighter than air, and consequently, the He gas flow floats upwards and inhibits transportation. Increasing the gas flow rate can reduce the floating of He and enhance the transportation of all reactive species in the He APPJ, but can only improve the transportation of short-lived species in the Ar APPJ. The use of shielding air gas reduces the floating of He and promotes the production of reactive species in the plasma plume, thus, the normalised concentration of the reactive species in the He APPJ-treated water increases drastically by 30.3 times. The numerical results conform to the trends observed in the available experimental data, which explains the reason why the Ar APPJ has stronger sterilization and anticancer effects than the He APPJ. The findings also serve as a reference for improving the He APPJ for biomedical applications.