Unsteady flow dynamics of a microwave plasma reactor

Microwave plasma reactors typically employ a swirling flow to shield the plasma from reactor walls. Gas heating from the microwave plasma affects the flow which affects heat transport and resulting temperature profiles. High-fidelity modelling of the flow can reveal mechanisms typically ignored in plasma fluid models.

Our 3D simulations of a typical MW plasma reactor were performed in PeleLMeX, an exascale-ready low-Mach computational fluid dynamics code, adapted to include the local field approximation and charge species transport. Microwave power is imposed via a constant applied field, defined so the resulting gas temperature matches measured temperature profiles. An N₂-O₂ kinetic scheme validated for microwave plasma is employed.

The deposited power heats up the gas at the center of the reactor, affecting the divergence of the velocity field. This also creates a backflow upstream of the power deposition and affects the axial velocity downstream. A quench gas, injected via perpendicular jets, is shown to not efficiently mix into the hot region. Adjusting the reactor geometry allows control over the temperature and residence times, improving yields of relevant species.