Momentum, heat, and neutral mass transport in convective atmospheric pressure plasma-liquid systems and implications for aqueous targets

Abstract

There is a growing interest in the study of plasma-liquid interactions with\napplication to biomedicine, chemical disinfection, agriculture, and other\nfields. This work models the momentum, heat, and neutral species mass transfer\nbetween gas and aqueous phases in the context of a streamer discharge; the\nqualitative conclusions are generally applicable to plasma-liquid systems. The\nproblem domain is discretized using the finite element method. The most\ninteresting and relevant model result for application purposes is the steep\ngradients in reactive species at the interface. At the center of where the\nreactive gas stream impinges on the water surface, the aqueous concentrations\nof OH and ONOOH decrease by roughly 9 and 4 orders of magnitude respectively\nwithin 50 $\\mu$m of the interface. Recognizing the limited penetration of\nreactive plasma species into the aqueous phase is critical to discussions about\nthe therapeutic mechanisms for direct plasma treatment of biological solutions.\nOther interesting results from this study include the presence of a 10 K\ntemperature drop in the gas boundary layer adjacent to the interface that\narises from convective cooling and water evaporation. Accounting for the\nresulting difference between gas and liquid bulk temperatures has a significant\nimpact on reaction kinetics; factor of two changes in terminal aqueous species\nconcentrations like H$_2$O$_2$, NO$_2^-$, and NO$_3^-$ are observed if the\neffect of evaporative cooling is not included.\n