Diagnostic of hydroxyl radical concentration in high pulse voltage triggered dielectric barrier discharges

Abstract

Experiments in a simple parallel-plate dielectric-barrier discharge show that the structure of monatomic gases is very differently from molecular gases. Time-resolved images show diffused discharge for monatomic gases and filamentary discharge for molecular gases. In addition, current waveforms also show a marked difference. monatomic gas the discharge is diffused compared to molecular gases. The high ionization coefficient at low reduced field, the high diffusion constant and the high secondary ionization coefficient of monatomic gases can account for these differences. derived which shows good agreement with experimental results for both monatomic and molecular gases. Two-dimensional streamer calculation show that in a Also an empirical relationship for power and voltage is This work was partially supported by funding from NSF 4P24 Diagnostic of hydroxyl radical concentration in high pulse voltage triggered dielectric barrier discharges C. Hibert, I. Gaurand, 0. Motret, M. Nikravech, R. Viladrosa and J. M. Orleans, BP 6759 45007 Orleans Cedex 2, France Pouvesle, University of Diagnostic of hydroxyl radical concentration in high pulse voltage triggered dielectric barrier discharges C. Hibert, I. Gaurand, 0. Motret, M. Nikravech, R. Viladrosa and J.M. Pouvesle. GREMp UMR 6606, University of0rlkun.s BP 6759 -15067 Orle'ans C'edex 2 -France Dielectric barrier discharges (DBDs) are well known to be non-thermal, cold discharges which are used in the treatment of different types of pollutants such as volatile organic compounds (VOCs) or flue gases.The hydroxyl radical ('OH) is a very efficient oxidant species and represents an important agent in the pollutant remediation. An estimation of potentialities of depollution processes involve notably a good kwnoledge of the hydroxyl concentration and its time evolution. Classically the *OH concentration measurements are realized by LIF principally in the earth atmosphere and in flames. This technique seems not to be very well adapted to filamentary DBD plasmas and represents a rather expensive investment.We have developed a diagnostic of absolute concentration measurement based on a time resolved resonant absorption spectroscopy. The probe signal 'OH(AZC+ -X'n, h = 308 tun) is generated in a high pulse voltage triggered DBD probe. The gas mixture (1 atm argon + 200 ppm water vapor) was optimized to adjust lifetime and intensity of the 'OH(A-X) UV fluorescence. This signal is sent through the main DBD plasma. After absorption, the output signal is used to calculate the 'OH(X) concentration in the main discharge. The delay between the onset of the main discharge and the probe pulse can be adjusted in order to probe the fondamental level 'OH(X) during the whole post-discharge. This diagnostic has been tested first in argon + water vapor mixtures. Various effects of discharge parameters like input energy or water vapor concentration on the 'OH(X) density have been clarified. Next more practical gas mixtures like air + water vapor + pollutant (TCE) mixtures have been investigated...

Nonequilibrium Plasma Reforming of Greenhouse Gases to Synthesis Gas

“…The experiments described above indicate that CO 2 and CH 4 conversion is promoted in their mixtures. A similar result was also recently reported in a pulsed DBD reactor . Hydrogen atoms from CH 4 decomposition are generally thought to facilitate CO 2 conversion (CO 2 + H → CO + OH).…”

“…With short high-voltage pulses, DBDs were evaluated for the conversion of CH 4 or CO 2 in pure gases with conversion rates up to 25% or 40%, respectively . DBD processing of CH 4 /CO 2 mixtures can lead to the formation of syngas . In a thermal plasma discharge (GlidArc), syngas production from CH 4 /CO 2 mixtures was reported with high efficiencies at atmospheric pressure .…”