Thermal characterization of a single microdischarge in atmospheric pressure air dielectric barrier discharges

This work investigates the effect and mechanisms of gas heating in atmospheric pressure air dielectric barrier discharges with experimental measurements and numerical models developed. The heating sources of a single microdischarge (MD) are evaluated by the 1.5D plasma fluid model (PFM) with heating mechanisms including elastic collisions, the ionic Joule heating, and kinetics considered. A 3D gas flow model (GFM) simulating the temperature distribution of the reactor with the convective effect of airflow considered is developed to verify heating sources calculated by comparing the simulated gas temperature with the rotational temperature determined from N-2 emission spectra measured. The source term of the energy equation in the 3D GFM is evaluated from the overall heating source calculated by the 1.5D PFM. The experimental average power consumption of the reactor is obtained and compiled statistically as 3.4 W. The average number of MDs in one cycle is compiled statistically as 140 MDs; therefore the average power consumption of a single MD obtained is around 0.024 W. The simulated power consumption of a single MD is around 0.028 W which agrees the average measured power consumption of a single MD. The heating sources of different mechanisms are evaluated by the 1.5D PFM and are provided as the average volumetric source term to the 3D GFM for evaluating the temperature distribution in the reactor. The simulated result shows that around 45% of power consumption is converted to thermal energy. The simulated average gas temperature at the center of the reactive zone is 460 K which agrees the rotational temperature determined as 470 K. Besides, both the simulated highest temperature and the temperature distribution of the reactor surface are close to those measured by the IR thermometer. The analysis of heating source finds that the ionic Joule heating and kinetics contribute to most of the heating source as 47% and 52%, respectively. Among the ionic species considered, O-2(+) the essential role and contributes to around 66% of the ionic Joule heating. Among the kinetics considered, exothermic processes contribute to most of the heating source as around 88%. Further analysis shows that the ozone generation and destruction reactions contribute to remarkable heating sources. The quenching processes of excited atomic oxygen and nitrogen species also contribute to noticeable heating sources and result in fast evolution of species densities. The N-2(v) and O-2(v) contribute to only a small percentage (similar to 10%) of the kinetic heating source under the operating conditions in this work.