Non-equilibrium modelling of arc plasma torches

Abstract

Abstract.A two-temperature thermal non-equilibrium model is developed and applied to the threedimensional and time-dependent simulation of the flow inside a DC arc plasma torch. A detailed comparison of the results of the non-equilibrium model with those of an equilibrium model is presented. The fluid and electromagnetic equations in both models are approximated numerically in a fully-coupled approach by a variational multi-scale finite element method. In contrast to the equilibrium model, the non-equilibrium model did not need a separate reattachment model to produce an arc reattachment process and to limit the magnitude of the total voltage drop and arc length. The non-equilibrium results show large non-equilibrium regions in the plasma -cold-flow interaction region and close to the anode surface. Marked differences in the arc dynamics, especially in the arc reattachment process, and in the magnitudes of the total voltage drop and outlet temperatures and velocities between the models are observed. The non-equilibrium results show improved agreement with experimental observations.

Formation of self-organized anode patterns in arc discharge simulations

“…This boundary condition is different from that used in [29], but is often adopted in arc plasma flow simulations, e.g., [31,21,72].…”

Basic knowledge on radiative and transport properties to begin in thermal plasmas modelling

“…The last works of Freton et al, Murphy et al, Wang et al, Trelles et al discuss this problematic for numerical modelling. 3,[110][111][112] Concerning the calculation of the 2T plasma compositions, the recent works highlighted the influence of several criteria on the determination of the number densities: non LCE and/or non LTE equilibrium 9,113,114 and the choice of the equations 115 to estimate the population are two examples. Nevertheless, Ghorui 116 mentioned that the thermodynamic functions and especially the specific heat at constant pressure were not really dependant of this last criterion for pressure lower than 10 atms.…”

Multi-Electrode Plasma Torches: Motivation for Development and Current State-of-the-Art

“…The equation set describing these variables are the NavierStokes equation (including the contribution by the Lorentz force density), the transport equation for the energy (incorporating the Joule heating due to the electric current flowing through the arc core, coupling thus the electromagnetic effect to the fluid dynamics), the mass continuity equation, the incompressibility/compressibility condition of the gas flow and the Maxwell equations for the electric and magnetic fields. The mentioned variables can be further extended with two scalar fields implementing the loss of momentum and energy due to turbulence (effect not very relevant to the gas flow within the torch [32,33]) and the electron temperature, the latter if non-equilibrium effects near to the electrodes or at the arc core fringes are to be included [34]. These equations and variables are solved for given boundary conditions, especially for a given mass flow at the inlet (with or without a swirl component) and the electric current (and in some models also the electric voltage) imposed externally on the torch.…”

“…After various complementing efforts by different research institutions worldwide probably the most advanced description of the thermal plasma within the single-cathode single-anode torch is that of the University of Minnesota [32,34] which also includes the separated solution of electric and heavy species temperature, incorporating some of the results derived for two-temperature transport coefficients calculated at atmospheric pressure [38].…”