Comparative analysis of turbulent effects on thermal plasma characteristics inside the plasma torches with rod- and well-type cathodes

Abstract

The thermal plasma characteristics inside the two non-transferred plasma torches with rod-type cathode (RTC) and well-type cathode (WTC) are analysed in conjunction with turbulent effects on them in the atmospheric-pressure conditions. A control volume method and a modified semi-implicit pressure linked equations revised algorithm are used for solving the governing equations, i.e. conservation equations of mass, momentum, and energy together with a current continuity equation for arc discharge. A cold flow analysis is introduced to find the cathode spot position in the WTC torch, and both the laminar and turbulent models are employed to gain a physical insight into the turbulent effects on the thermal plasma characteristics produced inside the two torches. The numerical analysis for an RTC torch shows that slightly different values of plasma temperature and velocity between the laminar and turbulent calculations occur and the radial temperature profiles are constricted at the axis with increasing the gas flow rate, and that the large turbulent viscosities appear mostly near the anode wall. These calculated results indicate that the turbulent effects on the thermal plasma characteristics are very weak in the whole discharge region inside the RTC torch. On the other hand, the calculated results of the two numerical simulations for a WTC torch present that the significantly different values of plasma characteristics between the two models appear in the whole torch region and the plasma temperatures decrease with increasing the gas flow rate because the relatively strong turbulent effects are prevailing in the entire interior region of the WTC torch. From the comparisons of plasma net powers calculated and measured in this work, the turbulent modelling turns out to provide the more accurately calculated results close to the measured ones compared with the laminar one, especially for the torch with WTC. This is because the turbulent effects are considerably strong in the WTC torch and subsequently govern the thermal plasma characteristics inside it.

Thermal Plasma Decomposition of Fluorinated Greenhouse Gases

“…(1) plasma characteristics in the arc discharge region of the torch interior are numerically analyzed by using a MHD (magnetohydrodynamics) code which has been developed to simulated thermal plasmas [46][47][48][49][50]. Second, the thermal plasma characteristics inside the decomposition reactor region where a complex thermal flow mixture between plasmas jet and waste gas is formed, can be precisely and stably simulated by using a commercial CFD (computational fluid dynamics) code, FLUENT (ANSYS), which has been widely used for solving complex hydrodynamic flows.…”

Control of the Nano-Particle Weight Ratio in Stainless Steel Micro and Nano Powders by Radio Frequency Plasma Treatment

“…Moreover, there are several assumptions in this simulation. (e) The K model of turbulence is adopted [23].…”

Effects of Constrictor Geometry, Arc Current, and Gas Flow Rate on Thermal Plasma Characteristics in a Segmented Arc Heater

“…The arc discharge and the thermal plasma jet generated in the segmented arc heater was simulated by using a magnetohydrodynamic (MHD) code, DCPTUN, which has been developed in the author's laboratory (4)(5)(6)(7)(8)(9) . For the numerical simulation, the governing fluid equations consisting of mass, momentum and energy conservation, were solved under the steady-state, two-dimensional, and axis-symmetric conditions.…”

“…In order to include radiation effects, optically thin plasma with the net emission coefficient in a local thermodynamic equilibrium (LTE) state was assumed (10) . Since the k-ε turbulence model has been widely used for a numerical modeling for the high velocity arc plasma jet, it was also incorporated to include turbulence effects inside the arc heater (4)(5)(6)(7)(8)(9)(10)(11) .…”