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Investigation of Thermal Nonequilibrium in a Plasma Arc Welding Process: Modeling and Diagnostics

In this paper, a plasma arc welding (PAW) process operating in pure Ar with constant current at 40 A has been characterized by means of a thermofluid-dynamic modeling and optical emission spectroscopy (OES). Excitation temperature of Ar atoms in the fringes of the arc measured using the OES has been found higher than temperature calculated from local thermodynamic equilibrium modeling, even if radiation reabsorption is taken into account using a discrete ordinate model; on the contrary, excitation temperature of Ar atoms is in a good agreement with electron temperature calculated using a two-temperature model for thermal nonequilibrium neglecting radiation reabsorption. Results reported suggest that for the investigated PAW process, thermal nonequilibrium due to steep radial temperature gradients induces a Boltzmann distribution of excited states at the electron temperature.