Abstract
Packed bed plasma reactors (PBPRs) inherently have complex geometries where the volume between the electrodes is filled with dielectric/catalytic pellets to form a large array of voids. While the dimension of the plasma region can be several centimeters, the size of a single void at the edges and pores of dielectrics/pellets can reach micrometer dimensions. The understanding of plasma propagation on these diverse length scales is essential for optimizing and controlling plasma processes performed in such discharges. It is known that plasmas are generated in PBPRs as multiple pulses due to cathode-directed positive streamers in the volume, surface ionization waves, or surface streamers over the dielectric surface and stationary microdischarges at the contact points of adjacent dielectrics. In this work, we have investigated the discharge formation and propagation as a function of applied voltage in simplified PBPRs with a single layer of hexagonally arranged hemispherical pellets, operated in helium, using phase and space resolved optical emission spectroscopy. Despite similar discharge conditions at multiple positions, the emission intensity during each pulse spreads like a wave from the center to the edges in the whole discharge cell. The emission due to surface ionization waves is significantly reduced compared to earlier works. These observations could be explained by possible interactions between adjacent microdischarges, already known in other arrays of microdischarges or adjacent streamers. Higher resolution images of the contact points show that the discharge has fine structures with stronger emission at the edges of the contact points; this effect is enhanced as a function of the driving voltage amplitude. This is possibly the consequence of non-uniform electric field distribution at the contact points due to the polarization of dielectrics.
Highlights
Non-thermal plasmas, such as dielectric barrier discharges (DBDs), are widely investigated for multiple environmental and biomedical applications.[1,2] Packed bed plasma reactors (PBPRs), in particular, are an attractive option for gas reprocessing applications, such as gaseous pollutant removal[3] and greenhouse gas valorization.[4]
A PBPR is a dielectric barrier discharge (DBD) in which the volume between the electrodes is filled with catalyst scitation.org/journal/adv respectively
Despite similar discharge conditions at all dielectric pellets positions, the emission intensity during each pulse spreads as a wave from the center to the edges of the whole reactor
Summary
Non-thermal plasmas, such as dielectric barrier discharges (DBDs), are widely investigated for multiple environmental and biomedical applications.[1,2] Packed bed plasma reactors (PBPRs), in particular, are an attractive option for gas reprocessing applications, such as gaseous pollutant removal[3] and greenhouse gas valorization.[4]. The combination of a plasma and a catalyst has been reported to work in a synergetic manner.[5] this results in a complex layout of the plasma source with a multitude of design and operational conditions and catalytic parameters that are difficult to understand, predict, and control.[6] There have been significant efforts in understanding the discharge formation in a single filament[7] or over the surface of a single pellet.[8] The multiple dielectric pellets and microdischarges in PBPRs are expected to change the electric field distribution and interact with the adjacent microdischarges, scitation.org/journal/adv respectively. These aspects could not be studied in a single filament or pellet and require investigation of a large array of dielectric pellets
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