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

This work numerically studies densities and mechanisms of OH species generated in atmospheric-pressure air dielectric barrier discharges with the model validated by experiments. The power consumption is measured, and the number of microdischarges (MDs) generated within a half period is captured by an intensified CCD camera. The OH densities of cases with various H2O concentrations are measured using ultraviolet absorption spectroscopy. The numerical model integrating the 1.5D discharge fluid model and 3D background gas model (BGM) is adopted to predict the MD behavior and the generation of species related to OH generation. The simulated OH densities cover the range of 1.1×10^19 and 1.6×10^19 m-3 in the cases studied, agreeing with those measured. The simulated results show that most OH radicals are generated in MDs, while the reactive section contributes around 2% of the total OH generation. The detailed analysis shows that atomic oxygen (O(1D) and O) and O3 contribute most of the OH generation in the MDs. In contrast, the self-association reactions (i.e., 2OH + M → H2O2 + M and 2OH → O + H2O) and NOx species consume more than 64% of OH radicals generated in MDs. In the BGM, it is interesting to find that reactive species NOx play significant roles in both the OH generation and depletion in the reactive section. The distributions of species related to the OH species obtained by the BGM are presented to elucidate the detailed chemistry of OH species in the reactive section.