Investigation of gas heating effect and induced pressure waves of a single microdischarge in atmospheric pressure dielectric barrier discharges

Abstract

This work investigates the gas heating process of a single microdischarge (MD) and the evolution of flow dynamics due to the induced pressure waves by using the transient 3D gas flow model of a single MD (GFM-MD) with the calculated heating sources validated. The heating sources of different heating mechanisms are calculated by the 1.5D plasma fluid model with the framework of air chemistry and provided as the source term of the energy equation solved in the steady-state 3D GFM-Reactor for obtaining the temperature distribution of the reactor to validate the overall heating source by comparing with experimental measurements. The validated heating sources in different temporal phases are provided as the volumetric heating sources in the sheath and bulk regions in the transient 3D GFM-MD to model the gas heating process and evolution of flow dynamics. The simulated power consumption of a single MD is around 0.068 W which is close to the average measured power consumption of a single MD as around 0.053 W. The average gas temperature in the central region of the reactive zone is around 440 K which agrees with the rotational temperature determined as 460 K. The maximum simulated surface temperature reaches 414 K which is in good agreement with that measured by the IR thermal imager as 435 K. The spatial average heating source increases dramatically to the level of 1011 W m−3 in a few ns during the breakdown (BD) phase from the low heating source of 107 W m−3 in the pre-BD. Detailed analysis shows that the kinetics and ionic Joule heating are dominant heating sources with comparable contributions. The heating source of the kinetics reaches the level of 1011 W m−3 across the gap with a moderate increase near the sheath region, while the heating source of the ionic Joule heating remains at a low level across the gap with a dramatic increase to the level of 1013 W m−3 in the sheath region in the BD phase, resulting in the rapid increase of gas temperature from 390 K to 550 K in the sheath region in a few ns. The dramatic increase of the ionic Joule heating in the sheath region in the BD phase results in the rapid increase of pressure to the level of around 1060 torr. An induced high-pressure wave is formed and moves from the sheath region to ambient air with the wave speed estimated as 410 m s−1 which is close to the speed of sound as observed experimentally. The high-pressure region results in a significant pressure gradient between the sheath region and ambient air in the gap, leading to an increase of the flow velocity. As air moves rapidly outward from the sheath region, the density in the sheath region decreases. The low-density zone in the sheath region results in the formation of a low-pressure wave after the induced high-pressure wave. The pressure waves move outward continuously, leading to the evolution of flow dynamics.