Propagation of positive discharges in an air bubble having an embedded water droplet

Abstract

Low temperature plasmas generated inside gas bubbles immersed in water is an effective method of rapidly transferring plasma generated reactive species to the water for applications in biomedicine, agriculture and environment. Reactive species are generally produced in the gas phase plasma and then solvate into the liquid. The large surface-to-volume ratio (SVR) of the bubble accelerates this process. In generating bubbles in water, aerosols and droplets are also contained within the bubble. These droplets also have a large SVR and so can be rapidly plasma activated. However, the presence of the droplets can also impact the propagation of the plasma in the bubble. In this paper, results are discussed from computational and experimental investigations of the formation and evolution of discharges in an air bubble immersed in water with an embedded water droplet. The computations were performed with a two-dimensional plasma hydrodynamics model. Experiments were performed with a quasi-2D bubble apparatus. In bubbles having a droplet, a plasma filament typically bridges from the powered electrode to the droplet, and then from the droplet to the bubble surface. A surface-hugging streamer also occurs on the inner bubble surface and on the surface of the droplet. Both surface streamers result in part from surface charge accumulation and can dominate the formation of reactive species that transport into the droplet. Increasing droplet conductivity suppresses propagation of the surface discharge and leads to a lower density of aqueous reactive species. Increasing conductivity of the surrounding water does not change the overall structure of the discharge but does slightly elevate the discharge intensity. The size and shape of the embedded droplet can significantly affect the formation and propagation of the streamer.

A review on plasma‐activated water and its application in the meat industry

“…This is the discharge of plasma in gas bubbles that are immersed in water. This is a promising plasma configuration to minimize the loss of reactive species due to mass transfer limitations at the gas–water interface (Man et al., 2022; Ning et al., 2021). The gas composition, bubble formation, and bubble size influence the discharge pattern inside the bubble (Meropoulis & Aggelopoulos, 2023; Ning et al., 2021).…”

Streamer dynamics and charge self‐erasing of two counter‐propagating plasmas in repetitively pulsed surface dielectric barrier discharge

“…It is difficult to completely understand the underlying mechanism of discharge plasma only by experimental measurement due to the limitation of diagnostic techniques. Numerical simulation provides a very meaningful and alternative choice to reveal the puzzles of the visual physical phenomenon [30,31]. For example, a two-dimensional (2D) fluid model is implemented to reveal the physical mechanism of two distinct streamer phases in pulsed pin-to-plane discharge, and find that the secondary streamer generates more active species compared to the primary streamer [32].…”

Global model of plasma‐activated water over long time scale: Pulsed discharge and afterglow

“…Tian et al investigated DBD discharge in wound treatment by a 2D simulation model [26]. Ning et al studied a two-dimensional quasi-steady bubble cavity containing liquid droplets in an electric field through experiments and 2D model [27]. Generally, a two dimensional model contains both temporal and spatial information, which is computationally intensive and is suitable for short-time (up to a few microseconds) analysis.…”