Modeling of inhomogeneous mixing of plasma species in argon–steam arc discharge

Abstract

This paper presents numerical simulation of mixing of argon- and water-plasma species in an argon–steam arc discharge generated in a thermal plasma generator with the combined stabilization of arc by axial gas flow (argon) and water vortex. The diffusion of plasma species itself is described by the combined diffusion coefficients method in which the coefficients describe the diffusion of argon ‘gas,’ with respect to water vapor ‘gas.’ Diffusion processes due to the gradients of mass density, temperature, pressure, and an electric field have been considered in the model. Calculations for currents 150–400 A with 15–22.5 standard liters per minute (slm) of argon reveal inhomogeneous mixing of argon and oxygen–hydrogen species with the argon species prevailing near the arc axis. All the combined diffusion coefficients exhibit highly nonlinear distribution of their values within the discharge, depending on the temperature, pressure, and argon mass fraction of the plasma. The argon diffusion mass flux is driven mainly by the concentration and temperature space gradients. Diffusions due to pressure gradients and due to the electric field are of about 1 order lower. Comparison with our former calculations based on the homogeneous mixing assumption shows differences in temperature, enthalpy, radiation losses, arc efficiency, and velocity at 400 A. Comparison with available experiments exhibits very good qualitative and quantitative agreement for the radial temperature and velocity profiles 2 mm downstream of the exit nozzle.

Modeling of argon–steam thermal plasma flow for abatement of fluorinated compounds

“…The diffusion coefficients were determined using the method of combined diffusion coefficients [52,53]. The calculated radial temperature profiles near the exit nozzle very well fit the experimental values, and, the velocity profiles also agreed well with experiment [47,48,50,51], whereas the predicted existence of supersonic flow was confirmed experimentally at currents 500 and 600 A [48,51]. The flow and heat transport strongly depends on the species distribution in the plasma that affect e.g.…”

“…For the radiation model, both the net emission coefficient method and the partial characteristic method [37][38][39][40] were used, while deviations from laminar flow were studied using the large-eddy-simulation (LES) turbulent model [41][42][43]. The numerical model showed the following findings: the tangential motion of the plasma affects the overall arc power and physical quantities only to a negligible extent [44,45]; at currents higher than 400 A, the plasma flow transits into the supersonic regime in the region close to the nozzle orifice [46][47][48]; the plasma flow exhibits the quasi-laminar structure close the nozzle orifice [42,43,49]; and, finally, at currents ranging from 150 to 600 A, steam and argon species are mixed together inhomogeneously in the discharge area nearby the nozzle orifice [50,51]. The numerical model considered diffusion due to density, temperature, pressure and electric potential gradients.…”

“…In contrast to our previous research [50,51], the present work focuses on numerical modeling of a modified hybrid DC plasma torch that can operate at powers up to 75 kW. Compared to the original discharge chamber geometry [48,50,51] the baffles with central holes for water have different shape and dimension, and circulation of water in the chamber is designed differently.…”

“…In contrast to our previous research [50,51], the present work focuses on numerical modeling of a modified hybrid DC plasma torch that can operate at powers up to 75 kW. Compared to the original discharge chamber geometry [48,50,51] the baffles with central holes for water have different shape and dimension, and circulation of water in the chamber is designed differently. Unlike the above-mentioned research [50,51], the outlet region for the plasma jet is extended to 20 cm from the nozzle, the plasma jet flows to the surrounding atmosphericpressure steam atmosphere contained in a plasma-chemical reaction chamber, the nozzle diameter is smaller (5.3 mm), and the range of currents is lower, from 120 to 220 A (20-40 kW).…”

Time-Resolved Emission Spectroscopy Measurements during the Restrike Period in Arc Plasma Torch

“…It is known that temperature distribution in the arc column is generally such that the maximum temperature is in the region between the electrodes from which temperature decreases with approaching to electrodes [20][21][22]. For this torch, we do not have experimental data of this type, but according to numerical models, such dependence along the axis of the torch is also present [23,24]. Such temperature distribution can simply explain the dependence as shown in Figure 6; as the arc attachment moves downstream, the position of measurement gets closer to the centre of the arc where the temperature is higher.…”