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Abstract |
We developed a thermo-chemical 2D axisymmetric model, describing turbulent fluid dynamics, heat transfer, species transport and chemistry, to gain insight into the fundamental mechanisms of CO2 conversion in MW plasmas. We validated our model against experiments for a range of flow rates (10–40 slm) and specific energy inputs (0.4–2.1 eV molecule???? 1) at atmospheric pressure, for straight tube experiments without constriction. We performed spatially dependent reaction analysis to assess the spatial dependence of CO2 conversion within the reactor, showing that net CO production happens at the edge of the plasma. Importantly, in contrast to assumptions in literature, net production and destruction rates do not balance each other, due to the radial diffusion of species. Furthermore, we investigated the effect of turbulence on the temperature profile, by comparing turbulent and laminar flow profiles. The additional turbulent thermal conductivity and turbulent diffusion lead to increased heat loss through the reactor walls. Overall, our model indicates the need for including radial diffusion and turbulence in multi-dimensional models of CO2 MW plasmas. Finally, our model predicts that at high flow rates (40 slm), turbulent diffusion may be a key driver for net CO transport into the cold gas stream at the reactor edges, after which it is convectively transported to the outlet. We hypothesize based on our calculations that by enhancing the turbulent effects, upon changing reactor design or gas flow dynamics, the net transport of the produced CO towards the cold edge of the reactor could be further promoted, increasing the overall CO2 conversion. |
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