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7314 |
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Thursday, May 05, 2022, Hall G1 3:00 PM Modeling & Simulation III |
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Effect of a cathode sheath model on the predicted behavior of electric arc in a cascaded-anode plasma torch |
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Rodion Zhukovskii* / University of Limoges, France Ron Molz / Oerlikon Metco (US), USA Christophe Chazelas/ Laboratory IRCER, University of Limoges, France Vincent Rat/ Laboratory IRCER, University of Limoges, France Armelle Vardelle/ Laboratory IRCER, University of Limoges, France |
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In a DC plasma spray torch, the cathode arc attachment is the location where the plasma-forming gas is the most intensively heated and accelerated due to the high electric current density. A proper prediction of the cathode arc attachment is, therefore, essential for understanding the plasma jet formation and cathode operation. However, plasma torch simulations are generally time- and resource-consuming and numerical studies of the cathode arc attachment are scarce and mostly deal with transferred arcs or conventional plasma torches with tapered cathodes. In this study, a time-dependent 3-D two-temperature electric arc model that integrates a cathode sheath model is applied to the commercial cascaded-anode plasma torch SinplexPro. The model is used to investigate the effect of a cathode sheath model on the predicted plasma flow and cathode arc attachment. The model of the plasma-cathode interface takes into account the non-equilibrium space-charge sheath to establish the thermal and electric current balance at the interface. First, the cathode sheath parameters (voltage drop, electron temperature at the interface, Schottky reduction of work function) were computed on the surface of the cathode tip and used at the cathode-plasma interface in the model of plasma torch operation. The latter model is developed in the open-source CFD software Code_Saturne. It makes it possible to calculate the flow fields inside and outside the plasma torch as well as the enthalpy and electromagnetic fields in the gas phase and electrodes. The study shows that the cathode sheath model results in a higher constriction of the cathode arc attachment, more plausible cathode surface temperature distribution and more reliable prediction of the torch voltage. |