Characterization of OH species in kHz He/H₂O atmospheric pressure dielectric barrier discharges

Abstract

This work investigates experimentally and numerically the chemical kinetics of OH species generated in kHz helium atmospheric-pressure dielectric barrier discharges with different H2O concentrations. The OH densities of cases are determined from measurements of the ultraviolet absorption spectroscopy (UVAS) system with transition parameters evaluated by LIFBASE. The 1D plasma fluid model (PFM) with compiled chemistry including the formation of charged cluster ions to capture the discharge dynamics for analyzing mechanisms of OH species properly. The simulated current densities of cases with 0.8% and 2.0% H2O concentrations increase from 29 to 51 A m-2, agreeing with experimental measurements. The simulated OH density increases from 1.5×10^19 m^-3 to 2.0×10^19 m^-3 as the H2O concentration increases from 0.4% to 2.0%, agreeing with OH densities interpreted from the UVAS system for cases with various H2O concentrations. The simulated results reveal that the electron and H2O+ are essential species for OH production through dissociative reactions (e + H2O -> e + OH + H) and (H2O+ + H2O ->H+(H2O) + OH) contributing to 61% and 23% of OH production, respectively. It is observed that the OH self-recombination reaction (OH + OH + He → H2O2 + He) contributes to 32% of OH consumption as the dominant reaction. Moreover, the stepwise recombination reactions (OH + H2O2 → H2O + HO2 and OH + HO2 → O2 + H2O) contribute to the overall 27% of OH consumption. As the essential species contributing to the OH production and consumption, a detailed analysis of electron and H species is conducted. The high average reaction rates of dissociative attachment reactions consume most of the electrons after the breakdown, which leads to the variation of discharge current density. The saturation of OH species is attributed to the transition of electron chemical kinetics and the recombination reactions of OH species.

Studies on plasma‐activated perilla seed oil: Diagnosis, optimisation, and validation of reactive species

“…After that, the generation and decay of OH reaches a dynamic equilibrium, and the OH density remains constant. As analysed earlier, under the action of a strong electric field, Ar gas discharge will generate a large number of high‐energy particles (excited Ar, N 2 , and e), and OH is mainly generated by the collision of high‐energy particles with surrounding water vapour [43–45]. After the discharge is switched off, the OH density decays exponentially, which is mainly depended by self‐destruction processes and reactions with other species [45, 46].…”

“…As analysed earlier, under the action of a strong electric field, Ar gas discharge will generate a large number of high-energy particles (excited Ar, N 2 , and e), and OH is mainly generated by the collision of high-energy particles with surrounding water vapour [43][44][45]. After the discharge is switched off, the OH density decays exponentially, which is mainly depended by selfdestruction processes and reactions with other species [45,46]. According to Figure 5a, about 50% OH radical quenched at 1 ms after the last pulse, and 75% OH radical quenched at 3 ms.…”

Characterization of OH species in kHz air/H2O atmospheric pressure dielectric barrier discharges

“…This work determines the OH densities by the UVAS developed in [23]. The UV light emitted from the LED (LCS-0310-03-23, Mightex) light source passes through the sidewalls of the reactive section and is then collected by an optical fiber located after the pinhole with a diameter of 1.4 mm to prevent the collection of stray light.…”

A comparative study on the spectral characteristics of nanosecond pulsed discharges in atmospheric He and a He+2.3%H2O mixture

“…to provide reactive species [10,11]. Among these gases, H 2 O in the vapor phase is an important reactive gas that adds to the gas mixture to produce hydroxyl radicals (OH), atomic oxygen and hydrogen, which plays a key role in the physicochemical processes [10,12,13].…”

“…With regard to He-H 2 O gas mixtures, various types of atmospheric-pressure plasma discharges, including dielectric barrier discharges [14], capacitive coupled discharges [7,15], nanosecond pulsed micro-discharges [16] and plasma jets [13,17] driven by power supplies with frequencies ranging from DC up to GHz, were studied via experimental diagnostics and numerical modelling. Among these, nanosecond pulsed micro-discharges in a pin-to-pin electrode configuration are of great interest, and have been studied intensively [10,16,18,19].…”