Effluent nozzles in reverse-vortex-stabilized microwave CO2 plasmas for improved energy efficiency

Energy efficiency and conversion in a reverse-vortex microwave CO 2 plasma are enhanced by optimizing the thermal trajectories using a converging diverging nozzle in subsonic flows. The nozzle mixes cold, unconverted gas at the edge of the flow with hot, active gas in the middle of the flow. Temperature measurements are taken of the quartz tube as well as just above the nozzle inlet and directly after the nozzle and presented to elucidate differences in performance. Measurements show significant improvements in conversion and energy efficiency, especially at pressures close to atmospheric pressure (500 – 900 mbar). In addition an improvement in plasma stability when adding a converging diverging nozzle. Thermal measurements also point towards a shift in energy loss mechanisms when changing flow configurations. • High energy efficiencies (up to 48 %) in CO 2 microwave plasma are achieved in subsonic flows. • Addition of a mixing nozzle increases plasma confinement. • Changes in energy loss channels when switching flow configuration are identified. • Radiative losses through the resonator are reduced by >90 % by changing flow configuration. • Cooling rates as high as 5.0×10 6 K/s are achieved by use of a mixing nozzle.