Simulation of the Axial III Plus Plasma Torch and Its Arc Fluctuations

Abstract

The demand for utilizing the Axial III Plus plasma spray system has prompted the numerical modeling of its arc plasma torch, integral to creating a digital twin of the suspension plasma spray process. The Axial III Plus plasma torch is a highly efficient and reproducible tool with a unique three-torch exit jet arrangement that allows the axial injection of solid/liquid feedstock, not possible with a single cathode/anode–plasma torch setup. In this study, we employ the local thermodynamic equilibrium approximation of the magnetohydrodynamic (MHD) model to simulate plasma flow inside the single gun plasma torch of Axial III, considering electrode–plasma interactions. Describing electric arc dynamics during restrike proves intricate; thus, a restrike model is used relying on cutoff criteria based on a threshold value E_b of the predicted radial electric field at the electric arc fringes. The model successfully replicates typical electric arc behavior and saw-toothed voltage profiles during restrike, notably capturing the characteristics of the Axial III anode’s unique and complicated design variations in electric arc motion and its corresponding arc voltage profile. Analysis extends to studying variations in E_b, which directly influence mean electric arc length, arc voltage, and mean arc spot time, potentially impacting energy generation and losses in the torch. These findings provide a valuable foundation for future simulations of this design, especially with swirl gas injection and ternary gas mixtures.