Visualization and analysis of coupling between plasmas self-organization and plasma-induced fluid circulation in 1 atm DC glows with liquid anode

Abstract

In plasma–liquid interactions, the phenomenon of induced liquid flow that originates at the plasma–liquid contact point is important in that it influences mass, charge, and heat transport from the source to the surrounding bulk fluid. Such stimulated flows have been observed in 1 atm glows with a liquid anode. Because the plasma contact point in such discharges is patterned, a natural question is what is the relationship between the observed self-organized patterns and the induced flow field? It is, therefore, of great interest to investigate the coupling mechanism between the self-organization patterns in an atmospheric pressure dc helium glow discharge with a liquid anode and the induced flow circulation. Particle imaging velocimetry is used to probe the flow fields in the plane normal and parallel to the plasma–liquid interface. A strong ascending flow with maximum speed up to 1.5 cm/s and circulation vortices nearby are observed in the plane normal to the interface centered at the plasma attachment. The experiment results suggested that the ascending flow is caused by water evaporation and the vortices are formed by viscous stress. With a self-organization pattern formed, the flow structures become non-static and the circulation vortices are observed to periodically form and decay. In the plane parallel to the interface, a strong swirl flow was found to exist only when the plasma attachment is self-organized. The analysis revealed that the driving mechanism could be the electrohydrodynamics force. Averaged flow velocity over time in the field of view was found to scale linearly with increasing input power and increasing liquid conductivity.

Low-temperature plasmas in contact with liquids—a review of recent progress and challenges

“…The conclusion is in line with Stancampiano et al who found that the origin of the vortex formation in the liquid is a consequence of EHD forces and gas flow tangential components [150]. Yang et al compared the plasma-induced liquid flow observed under DC discharge with that observed in plasma jets, which do not have significant heat transport [156]. Using the technique of PIV, in the case of DC glow discharge, they recorded upward liquid flow toward the point of plasma-liquid interaction and a circle of vortices nearby, with velocities in the range of cm s −1 .…”

“…The authors also studied formed self-organization patterns and its influence on the liquid flow structures. With the formation of the patterns, flow structures become nonstatic and the circulation vortices are observed to periodically form and decay [156].…”

Self-organized patterns at the plasma–liquid anode interface in a helium glow discharge: temporal development and mechanisms

“…Kovach et al [11] report that upon increasing the discharge current, the pattern formation transitions from a nitrogen-dominated emission regime to an OH-dominated emission regime, suggesting that evaporation might be important for pattern formation. Yang et al [12] have observed a strong swirl flow in a plane parallel to the plasma-liquid interface only for cases for which the patterns are observed which could be caused by electrohydrodynamic forces due to surface charging. Chen et al [13] suggest that the gas temperature in the bulk of the discharge along with the temperature of both the electrodes, the metallic cathode and the solution anode, can enhance pattern formation.…”

Various concentric-ring patterns formed in a water-anode glow discharge operated at atmospheric pressure

“…The plasma attachment to a water electrode is apt to be uniform, presenting a disk shape in the interface between the glow plasma and the water electrode [15]. Other than the uniform disk, some discrete spots can also be formed above a water electrode [16]. Under proper conditions, some self-organized patterns appear, especially above a water anode [17,18].…”