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A plug-flow reactor model accurately calculates atomic-oxygen number densities at the exit of Ar-O2 dielectric-barrier discharges, revealing that wall-loss frequencies of O atoms deviate by orders of magnitude from existing literature data. Novelty: ClaimNovelty.METHODOLOGICAL. Consensus alignment: ConsensusAlignment.CHALLENGES_CONSENSUS.

November 17, 2022Open Access

Atomic-Oxygen Number Densities in Ar-O2 DBDs and Post-discharges with Small Initial O2 Fractions: Plug-Flow Model and Experiments

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Abstract

Abstract Number densities of oxygen atoms, n O, in Ar-O 2 mixtures with small initial O 2 fractions, x₎₂ x O 2 x O 2 = 100 ppm. For such low O 2 fractions, the time-dependence of n O in the DBD and the early PD can be calculated by a closed equation. Calculations are compared with optical emission spectroscopic (OES) results, utilizing the proportionality of O-atom emission intensity at 777. 4 nm to n O. O-atom densities in the PD are made accessible to OES using a tandem setup with a second DBD as sensing discharge. Model testing by experiment is based on the functional dependence of n O on DBD-residence time and PD-delay time, respectively. Wall losses of O atoms in asymmetrical DBD reactors are calculated by an alternative to Chantry’s equation. The agreement between O-atom densities attained at the DBD exit and experimental results is generally good while the speed of rise of n O in the discharge is overestimated, due to the assumption of a constant wall-loss frequency, k W. Compared with literature data, k W is orders of magnitude higher in the DBD and at least one order of magnitude lower in the PD.

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