Mode Transition of Filaments in Packed-Bed Dielectric Barrier Discharges

Abstract

Abstract:We investigated the mode transition from volume to surface discharge in a packed bed dielectric barrier discharge reactor by a two-dimensional particle-in-cell/Monte Carlo collision method. The calculations are performed at atmospheric pressure for various driving voltages and for gas mixtures with different N 2 and O 2 compositions. Our results reveal that both a change of the driving voltage and gas mixture can induce mode transition. Upon increasing voltage, a mode transition from hybrid (volume+surface) discharge to pure surface discharge occurs, because the charged species can escape much more easily to the beads and charge the bead surface due to the strong electric field at high driving voltage. This significant surface charging will further enhance the tangential component of the electric field along the dielectric bead surface, yielding surface ionization waves (SIWs). The SIWs will give rise to a high concentration of reactive species on the surface, and thus possibly enhance the surface activity of the beads, which might be of interest for plasma catalysis. Indeed, electron impact excitation and ionization mainly take place near the bead surface. In addition, the propagation speed of SIWs becomes faster with increasing N 2 content in the gas mixture, and slower with increasing O 2 content, due to the loss of electrons by attachment to O 2 molecules. Indeed, the negative O − 2 ion density produced by electron impact attachment is much higher than the electron and positive O + 2 ion density. The different ionization rates between N 2 and O 2 gases will create different amounts of electrons and ions on the dielectric bead surface, which might also have effects in plasma catalysis.

Discharge Enhancement Phenomenon and Streamer Control in Dielectric Barrier Discharge with Many Pores

“…The pore size increases from 0 × 0 mm to 0.08 × 0.16 mm, surface discharge becomes dominant, and the maximum value of the O + 2 density is 1.3 × 10 23 m −3 , all of which agree with the predictions in Ref. [60]. These high-density ions could be used for improving the efficiency of the plasma catalysis process.…”

“…. The pore size increases from 0 × 0 mm to 0.08 × 0.16 mm, surface discharge becomes dominant, and the maximum value of the O + 2 density is 1.3 × 10 23 m −3 , all of which agree with the predictions in Ref [60]…”

Spatially and temporally non-uniform plasmas: microdischarges from the perspective of molecules in a packed bed plasma reactor

“…We acknowledge that we do not capture the actual physics of a microdischarge, and we do not consider an actual plasma, which could influence charged particles, especially in the microdischarges due to the presence of strong electric fields. Indeed, self-consistent modelling of a filamentary plasma is a difficult task, requiring e.g., particle-in-cell Monte Carlo methods [19]. As we consider millions of random microdischarges instead of individual microdischarges, a fully self-consistent filamentary plasma model is not feasible.…”

Plasma-enhanced catalysis for the upgrading of methane: a review of modelling and simulation methods

“…The PIC-MCC approach has also been used to simulate a surface discharge on dielectric beads by Gao et al, however for an air plasma. 152 Although not modelling a methane plasma, the work merits mention due to its direct relevance to plasma-catalysis, investigating mode transitions of filamentary discharges in packed bed DBD reactors. The ionisation and excitation rates obtained for nitrogen and oxygen are presented in Figure 12, where they are shown to be more pronounced on the surface of the dielectric beads.…”