Self-Consistent Cathode–Plasma Coupling and Role of the Fluid Flow Approach in Torch Modeling

Abstract

A two-dimensional and stationary magnetohydrodynamic model of a plasma spray torch operated with argon is developed to predict the plasma properties in a steady operating mode. The model couples a submodel of a refractory cathode and its non-equilibrium boundary layer to a submodel of the plasma in local thermodynamic equilibrium in a self-consistent manner. The Navier–Stokes equations for a laminar and compressible flow are solved in terms of low and high Mach number numerical approaches. The results show that the Mach number can reach values close to one. Simulations are performed for electric currents of 600 A and 800 A, and gas flow rates of 40, 60, and 80 NLPM. The plasma parameters obtained by the two approaches differ, and the differences become more pronounced for higher currents and gas flow rates. The arc voltage, the electric power, and the thermal efficiency from both the low and high Mach number models of the plasma agree well with experimental findings for a current of 600 A and a flow rate of 40 NLPM. For higher currents and gas flow rates, the results of the low and high Mach number models gradually differ and underline the greater appropriateness of the high Mach number model.

Effect of a Spatially Fluctuating Heating of Particles in a Plasma Spray Process

“…The present work continues the plasma spraying related studies that have started with a model of the plasma spray torch Oerlikon Metco F4MB-XL [46]. Here, a particle tracing model along with a turbulent model of the plasma jet in the plume region of a plasma spray torch are employed.…”

“…At the exit of the plasma torch BB´ (Fig. 1), the values of the temperature, T, and the z-component of velocity, w, are taken from the previously published model of the plasma torch [46], while the radial velocity is set to zero. A turbulence intensity I T = 0.16R e − 1 8 and a turbulent length scale L T = 0.07l with l being a characteristic length taken as the diameter of the nozzle exit BB' [58] are set.…”

“…In a recent work [46], we reported on a self-consistent coupling of the thermionic cathode and its non-equilibrium boundary layer with the bulk plasma in the state of local thermodynamic equilibrium inside the plasma torch Oerlikon Metco F4MB-XL [47], as well as on the impact of the flow description on the predictive capability of a model of the plasma torch. It was shown that the cathode-plasma coupling is essential for the agreement with experimental data with respect to the arc voltage and electric power, while the high Mach number fluid flow approach improves the prediction with respect to the thermal efficiency of the plasma torch.…”

In-Flight Mechanisms in Suspension Plasma Spraying: Issues and Perspectives

“…If none of the models integrates all the phenomena that occur in the plasma spray process, the most advanced ones produced realistic predictions that can help to better understand the process ( Ref 60,61,71,73). To model the process in a representative way, each subsystem described in section 5 must be accurately modeled, which will inevitably lead to very heavy numerical simulations.…”

Numerical modelling of a direct current non‐transferred thermal plasma torch for optimal performance

“…[27][28][29] On the other hand, Baeva et al in their 2D steady laminar model did self-consistent coupling of cathode's non-equilibrium boundary layer to a fluid model of the plasma in LTE (local thermodynamic equilibrium). [30] However, none of the aforementioned studies has considered the effect of convective heat transfer coefficient (h) on the temperature, velocity profiles, thermal efficiency, and optimal operation of the plasma torch. Also, there is a lack of studies that pointedly analyse the changes that electromagnetic forces and their coupling with fluid flow introduce in the plasma gas, resulting in a constricted high-speed jet.…”