11th East Asia Joint Symposium on Plasma and Electrostatic Technologies for Environmental Application (EAPETEA-11)

In this work, a three-dimensional computational fluid dynamics model is developed for a vortex-stabilized microwave CO₂ plasma reactor operating over the pressure range of 100- 400 mbar. The model combines experimentally constrained, emission-based plasma sizes and volumetric heat-source distributions with thermally dominated finite-rate heavy-particle chemistry for a multi-component mixture. Turbulent flow and transport are described using the SST k-ω model.  The model reproduces the measured radial gas-temperature profiles in the plasma core and the non-monotonic pressure dependence of CO₂ conversion, including a maximum at 150 mbar and a pronounced decrease at 400 mbar. A detailed analysis of the optimal operating condition at 150 mbar reveals that CO₂ dissociation efficiency is governed by a strong synergy between flow dynamics, thermal fields, and reaction kinetics (Fig. 1). A vortex-driven recirculation region redistributes gas upstream. Turbulent mixing and cooling are strongest near the upper reactor boundary, but their contribution decreases as pressure increases. The pressure dependence of conversion is determined by the competition between CO₂ dissociation and CO recombination. CO₂ direct dissociation reaction dominates in the high-temperature plasma core, whereas O-assisted conversion reaction contributes near the plasma edges and in the surrounding hot region. At 150 mbar, enhanced CO₂ dissociation is accompanied by limited CO loss, resulting in the highest conversion. With pressure increasing to 400 mbar, slower cooling and more frequent three-body collisions promote CO recombination in the afterglow, causing more than 60% of the CO formed near the plasma to be lost downstream. Moreover, additional CO loss occurs in the upper region of the reactor at higher pressures because of the reduced cooling rate.
 

CFD,CO2 dissociation,Microwave plasma,CO2 dissociation,pressure-dependence