Anode spots of low current gliding arc plasmatron

Abstract

In this work a gliding arc plasmatron consisting of a filamentary discharge rotating in a nitrogen vortex flow at low DC current (I = 100 mA) is investigated. The gas flow swirl of the plasmatron is produced by six tangential gas inlets. The Reynolds number of the nitrogen flow through these tubes at the flow rate of Q = 10 slm amounts to about 2400, which is in the intermediate range. Under these conditions, the formation of micro-vortices can be caused by small gas flow disturbances like e.g. a tube edge. The operation of the GA plasmatron at these conditions is accompanied by the production of plasma spots at the anode surface, namely near the gas inlets. Melted and solidified metal is found in erosion traces left by plasma spots at the anode surface. It is established that melting of stainless steel cannot be caused by an axial current of I = 100 mA of plasma spots and an helical current is supposed. This assumption is confirmed by microscope images of eroded traces with toroidal melting areas. These experimental results corroborate a hypothesis of previous studies, concerning the gliding arc physics, about the formation of plasma objects with an axial magnetic field by the interaction of micro-vortices with the plasma channel.

Formation and behaviour of plasma spots on the surface of titanium film

“…Recently obtained experimental results by different groups studying gliding arc (GA) properties, confirm the existence of this effect, specifically the formation of plasma objects with an axial magnetic field caused by the interaction of microvortices with a filamentary discharge, like a GA [16][17][18][19]. A formation of plasma objects, named 'arc lump', has been established by the interaction of micro-vortices with an AC GA channel [16].…”

“…Based on previous studies on plasma spot core formation [7,10,14,16,19], it was assumed that a cold plasma contracts by an interaction with micro-vortices. This idea is tested in the presented study by treating a titanium film with an N-APPJ operated in argon and krypton flow.…”

“…Moreover, positive ions detected spectroscopically inside of the plasma plume possess considerably higher kinetic energy than expected under the established plasma conditions. Furthermore, a toroidal erosion of the plasmatron anode, caused by toroidal heating of anode spots, was observed in [19]. It is believed that the toroidal current of anode spots is caused by an interaction of micro-vortices produced at the tangential gas inlets of the plasmatron with the GA channel.…”

“…Summarizing, an axial magnetic field is the most feasible interpretation to the observed physical effects. These effects include the spatial alignment of an arc lump [16], a large helical current, high kinetic energies of ions and neutrals (high gas temperature) of the plasma plume [16] and a toroidal heating of the anode spot in the GA plasmatron [19].…”

Systematic Simulation Strategy of Plasma Methane Pyrolysis for CO2‐Free H2

“…The streamlines are smoother with the larger inlet diameter, while with the smaller diameter gives rise to more eddies at the location where the arc is supposed to ignite. The simulations can thus be used to justify increase of the inlet diameter 34.…”