Non-equilibrium simulation of the spatial and temporal behavior of a magnetically rotating arc in argon

Abstract

A three-dimensional model of a dc plasma torch with a rod-type cathode at atmospheric pressure has been developed in order to study a magnetically rotating arc in argon. The interplay between the arc and the plasma flow is described by means of magnetohydrodynamic equations in combination with a K-turbulence model. The simulation study is performed in terms of a two-temperature description (different electron and heavy particle temperatures). In the absence of magnetic field, the electron and heavy particle temperatures are nearly identical in the arc core, while near the walls, in the arc fringes and in the plume there are significant differences. With the magnetic field present, deviations from LTE appear even in the arc core and electron and heavy particle temperature differ there by about 10% thus emphasizing the need for a two-temperature treatment. The high temperature plasma region constrains in the axial and expands in the radial direction. The gas temperature gets lower by 2000 K in the arc core. In a moderately strong magnetic field, the magnetically driven plasma rotation is resolved and deviations from the axial symmetry are observed. Results for plasma and flow parameters are obtained and discussed.

Account of near-cathode sheath in numerical models of high-pressure arc discharges

“…Other papers, viceversa, assume T e = T h but do not assume ionization equilibrium; e.g., [18][19][20][21][22]. Finally, there are fully non-equilibrium models, which rely on assumptions of neither thermal nor ionization equilibrium; e.g., [23][24][25][26][27].…”

Nonequilibrium Modeling of Steam Plasma in a Nontransferred Direct-Current Torch

“…The region near the electrode surface exhibits a low plasma temperature except for the arc root location, where the dominant Joule heating effect contributed by the substantial current density explains the sudden temperature rise. In contrast with the RTC torch, which exhibits a maximum temperature of up to 20 kK near the cathode tip [10], the WTC torch constrains the extreme temperature region to be along the torch axis and can thus significantly reduce the thermal loading on the electrode surfaces. The plasma temperature near the electrode spot is predicted to be less than 10 kK in this paper.…”

“…T C can be either the plasma temperature (T ) or the electron temperature (T e ), depending on the nature of the chemical reaction. The constants that appear in (10) can be found in [14] and references therein. Table III summarizes the equation constants of (10).…”

“…The flux i of neutral species i is defined as (10) where D i is the diffusion coefficient of neutral species i . The energy equation of electrons applied to the calculation of the electron temperature in the thermal plasma flow is (17) where ε e denotes the mean electron energy (= 3/2k B T e ), E inel,l is the electron energy loss due to inelastic collisions in reaction l, K inel,l is the rate constant of inelastic collisions in reaction l, K el, j denotes the rate constant of elastic collisions of electrons with neutral species i, m e is the electron mass, and m i is the atomic or molecular weight of neutral species i .…”

“…Despite significant progress in the study of thermal plasma flows, with satisfactory prediction accuracy having been demonstrated in [2]- [7], the aforementioned LTE approach, which ignores the differences in energy supply between charged and neutral particles, can substantially underestimate the electron temperature in regions with low plasma temperature, where the LTE condition is not satisfied. Reference [10] that theoretically investigated the thermal behavior of an argon plasma in a dc torch with a roottype cathode (RTC) highlighted this situation. The electrons were found to be quite energetic in some low-temperature regions of the plasma because of the presence of an external magnetic field, which implied a substantial deviation from the LTE assumption.…”