DC Plasma Torch Research Articles

Basic model for calculating the macroscopic temperature of plasma plume and comparison with electron excitation temperature by optical spectroscopy method for non-transferred DC plasma torch

Basic model for calculating the macroscopic temperature of plasma plume and comparison with electron excitation temperature by optical spectroscopy method for non-transferred DC plasma torch

Effects of Gas Components on the Jet Characteristics of a DC Plasma Torch by Using Orthogonal Test Method

Effects of Gas Components on the Jet Characteristics of a DC Plasma Torch by Using Orthogonal Test Method

Modelling of thermal plasma-assisted carbon tetrafluoride abatement

This study focuses on the numerical modelling of the decomposition process of carbon tetrafluoride (CF4, Freon R-14), the most stable perfluorinated gas with a significant global warming potential, as experimentally carried out using a thermal argon/steam plasma in a plasma-chemical reactor. The numerical modelling approach incorporates advanced computational fluid dynamics (CFD) techniques and the kinetics of a complex chemical reaction mechanism. A two-dimensional axisymmetric model, incorporating the conservation of mass, momentum, energy and chemical balances, has been developed to simulate the species distribution under the assumption of steady flow, including turbulence effects. In order to compare the species distributions and destruction efficiencies, two chemical reaction mechanism models of different complexity were implemented: a simplified model A with 196 reactions and a model B with 258 reactions. The simulations were performed for plasma generated by steam and argon stabilized DC plasma torch under three operating conditions for arc currents of 120, 150 and 200 A. The destruction and removal efficiency (DRE) of CF4 decomposition at a high feed rate was computed by both models, with an error of less than 6% compared to the experimental data. It can be concluded that both models accurately predict the residual CF4 concentration trends depending on the feed per input torch power. While model A overestimates process efficiency, model B, with a more balanced reaction mechanism, more closely aligns with experimental results. Model B provides an accurate prediction of the DRE and captures trends as a function of input parameters. Importantly and innovatively, the model presented in this study, unlike previous models, allows for the first time the inclusion of both high concentrations and a sufficiently large reaction mechanism for CF4 abatement. This model presents a novel opportunity to perform trend simulations of operating characteristics for the CF4 abatement problem at a quantitative level, allowing experimental design to be evaluated and optimised.

Effect of chamber pressure on the output characteristics of a low-pressure DC plasma torch

This study explores the effects of chamber pressure on the electrical and thermodynamic characteristics of a low-pressure thermal plasma jet. The investigation focuses on current–voltage characteristics, arc voltage fluctuations, plasma jet temperature, electron density, and velocity within the range of 100–500 A arc current, at chamber pressures of 100 Pa, 1 kPa, and 3 kPa. Spectral analysis of the arc voltage reveals the presence of distinct frequencies, including restrike, Helmholtz, and acoustic modes, which exhibit varying behavior under different chamber pressure conditions. Restrike frequency shows an increase with decreasing chamber pressure, while Helmholtz frequency remains unaffected, and the power density of the acoustic frequency diminishes, eventually disappearing from the spectrum. The transition of the plasma jet from a continuum regime to a frozen state with decreasing chamber pressure is observed along with its shock structures. Optical emission spectroscopy is utilized to map the excitation temperature and electron density profile along the jet axis, demonstrating that the jet temperature and density peaks at the compression zone. Furthermore, Mach probe measurements of the plasma jet velocity at different axial locations, under various chamber pressure conditions, illustrate that the plasma jet maintains a supersonic state, regardless of chamber pressure. However, after the formation of a Mach disk, the jet velocity becomes subsonic. The highest velocity is achieved at 100 Pa chamber pressure, reaching Mach 2.9 at 50 mm from the anode exit. This research enhances our understanding of thermal plasma jets under low-pressure conditions, contributing to the advancement of knowledge in their applications across various domains.

Decoration of Graphene in Plasma Jets of a DC Plasma Torch for 2D Printing

Decoration of Graphene in Plasma Jets of a DC Plasma Torch for 2D Printing

Research of the Binding of an Argon Arc to the Cathode in a DC Plasma Torch

Research of the Binding of an Argon Arc to the Cathode in a DC Plasma Torch

Application of similarity theory to predict operational characteristics of a DC plasma torch under low-pressure condition

Application of similarity theory to predict operational characteristics of a DC plasma torch under low-pressure condition

Numerical analysis of direct-current (DC) plasma processing for high-efficient steel surface modification

Nowadays, direct-current (dc) non-transferred arc plasma torch has drawn significant interest from both academia and industry due to the capability to process products in an efficient and convenient way. The core of this technology is to clarify and manipulate the arc behavior at the interior of the dc plasma torch to produce ideal plasma jets for processing. To solve this problem, a quasi-steady axisymmetric model is built to simulate and compare the arc characteristics in different operating conditions and different nozzle structures of the plasma torch. The results uncover distinct aspects of the study on arc characteristics, including the detection of the primary arc attachment region and its spatial features caused by the choking effect of torch structure. The thermal efficiency focused on processing substrate is also calculated in this paper for estimating the performance of plasma processing. The calculated results show that increasing the mass flow rate brings better thermal efficiency and the greatest promotion is at least 6% in the same current value, whereas improving the arc current value causes the opposite result. Meanwhile, two types of nozzle are compared to the original design in thermal efficiency, where the wide nozzle is chosen for torch optimization due to its best power efficiency. The secondary arc attachment on the metal substrate is discovered though its impact scope is only within a radius of 10 mm from the torch axis, its effect on the processing could be ignored for the extremely low electric current value.

Design and Experimental Jet Characteristics of an Optimized DC Plasma Torch

Due to their favorable jet characteristics, direct current (dc) thermal plasma torches have been used to meet the different requirements of variety applications. For obtaining more favorable jet characteristics and longer service life, variety design considerations of thermal plasma torches, e.g., cascade anode, multicathodes, and multianodes, have been used and studied by experiments and simulations. However, how the design considerations influence the jet characteristics and how about the coupling relationships of the working conditions should be studied systematically. Therefore, some key design tips have been discussed and applied to optimize a home-made thermal plasma torch first. Then, the experimental setup and methods for obtaining the jet characteristics of the optimized plasma torch have been introduced in detail. Finally, the experimental jet characteristics of the optimized plasma torch and the coupling relationships of the working conditions have been obtained and discussed. The study results show that: 1) the thermal plasma torch could obtain good jet characteristics and long service life by adopting the design tips and 2) the coupling relationships of the working conditions have been obtained and discussed, which could be helpful for predicting the jet characteristics of a thermal plasma torch.

Coal Tar Pitch Processing: Experimental and Theoretical Characteristics of Thermal Plasma Process Using DC Plasma Torch

Coal Tar Pitch Processing: Experimental and Theoretical Characteristics of Thermal Plasma Process Using DC Plasma Torch

Investigation on spheroidization of refractory tungsten powders by laminar DC plasma torch

The spherical tungsten powders were prepared by a low-power DC laminar plasma torch. At a discharge current of 50 A, the tungsten powder fed downstream cannot be spheroidized by using Ar discharge, while a small number of spherical particles can be observed with upstream feeding. When N2 is added to the working gas, the input power is increased to maintain the same discharge current, which leads to the increase of plasma jet length, thereby expanding the effective high temperature region. Optical emission spectroscopy measurements show that the electron excitation temperature of N2-Ar mixed discharge is higher than that of argon discharge. In addition, compared with argon plasma, N2-Ar mixed gas plasma has larger thermal conductivity due to the molecular dissociation. Therefore, the heat is more efficiently transferred from the plasma to the tungsten particles. The improvement of plasma jet and heat transfer characteristics by introducing nitrogen into the discharge contributes to the increase of spheroidization rate. EDS analysis shows that the oxygen content in the tungsten particles decreases after spheroidization, which is caused by the evaporation of tungsten oxide during plasma treatment.

Thermal plasma assisted pyrolysis and gasification of RDF by utilizing sequestered CO2 as gasifying agent

A growing global population coupled with rising industrialization has led to an ever increasing energy demand, which in turn forced us to turn to fossils without sufficient consideration of the consequences. The most serious consequence, as is evident today, is the increase in CO2 levels responsible for adverse climate change, which compelled the United Nations to develop the Sustainable Energy Goal 13 (SDG-13), calling for immediate action to combat climate change and its effects. On the other hand, the increase in population has also resulted in a tremendous increase in waste generation, necessitating the need for safe and sustainable waste treatment. Over recent years, research has been concentrating on advanced thermal plasma technology to valorize diverse wastes into useful energy. The generated syngas can be utilized for energetic (such as heat and electricity) and chemical (such as methanol and dimethyl ether) end applications. The current investigation analyzes the viability of the thermal plasma system (a water-stabilized DC plasma torch) for the pyrolysis, partial pyrolysis, and gasification of refuse-derived fuel (RDF) coupled with the implementation of the CCUS concept using waste CO2 as a gasifying agent (which is planned to be separated from flue gas coming from waste combustion) and converting it into CO in the syngas through plasma valorization of RDF. A comparative evaluation of the attributes, impurities, and yield of syngas and the generation of solids (ash and char) is carried out along with the analysis of performance parameters for four different cases (with variable inputs of CO2, namely 173, 62, 26 and 0 L/m with gasification ratio ranging from 1.04 to 0.4). The syngas constituents are compared to the equilibrium compositions deduced by developing an equilibrium model in Aspen Plus (V 11.0) thermodynamic environment and are found to be close to the theoretical compositions. The highest gas yield is found for Case-I with 3.44 m3/kg due to the maximum carbon conversion, while the minimum gas yield is assessed as 1.60 m3/kg for Case-IV with high char production. Furthermore, H2 production was found to be almost the same for all cases (1.06–1.12 m3/kg of fuel). Furthermore, energetic efficiencies for all the four cases (63 %, 60 %, 62 % and 58 %) clearly reveal an encouraging energy balance. The theoretical maximum values of contaminants such as NH3, H2S, HCl, HF and HBr are calculated and a design of a syngas cleaning system is proposed. The promising results of the study can be considered a small but significant step towards SDG-13.

Low-friction, wear-protecting coatings on polymers by atmospheric pressure plasma spraying

Deposition strategies to obtain low-friction and wear resistant coatings on 3D-printed rough polyamide 12 (PA12, nylon) surfaces were developed via atmospheric pressure plasma deposition. The feedstock materials for the DC plasma torch InoCoat 3 produced by INOCON Technologie GmbH were dry lubricants such as MoS2 and graphite. In addition, parameter sets that would not thermally damage the heat sensitive polymers were applied. Generally, microtribological characterisation indicates that coating composition and thickness particularly influence the coating performance significantly. Pure MoS2 coatings wear rapidly, particularly on the roughness tips (mean substrate roughness Ra up to 20 μm); this exposes the substrate and leads to friction coefficients similar to those of PA12 and rather limited potential for protection against wear. Composite coatings with graphite in a MoS2 matrix provide huge potential for wear protection (i.e. >20 times less penetration depth) even for exposed PA12 roughness tips, owing to the transfer of lubricating carbon into these exposed areas. If the thickness is sufficiently high, preventing the wear of tips results in low-friction properties (friction coefficients < 0.1, i.e. four times lower than those for uncoated PA12).

Experimental study on the effect of argon shielding gas on the suppression of nitrogen arc anode ablation

The high heat flux density of the DC arc often leads to severe anode ablation, which is a key factor limiting the wider use of the DC plasma torches. In this study, a series of comparative experimental studies are conducted with the goal of suppressing nitrogen arc anode ablation by combining argon shielding flow and anode structure. It is found that for the planar electrode structure, the use of argon shielding gas can alleviate the ablation of the anode by nitrogen arc to some extent. If a boron nitride channel is installed on the anode surface to constrain the argon shielding flow, the electrode ablation can be significantly reduced. The experimental results show that there is no significant ablation on the anode surface after 1 h of operation of the nitrogen arc device with an arc current of 100 A. Further analysis reveals that, on the one hand, argon shielding gas can extend the range of motion of the nitrogen arc root along the anode surface and increase the speed of arc root motion, which has the effect of expanding the time-averaged arc anode attachment area. On the other hand, argon shielding gas can also increase the size of the nitrogen arc root and decrease the temperature of the arc root. The use of constraining channels can effectively control the range of motion of the arc root along the anode surface and strengthen the influence of argon shielding gas. The combination of these effects can substantially suppress the anode ablation of the DC arc device.

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

This study presents a numerical model of the hybrid-stabilized argon–steam thermal DC plasma torch of a new design for generating an argon–steam plasma suitable for efficient abatement of persistent perfluorinated compounds. The model includes the discharge region and the plasma jet flowing to the surrounding steam atmosphere contained in a plasma-chemical chamber. Compared to previous studies, the torch had a smaller nozzle diameter (5.3 mm) and a reduced input power (20–40 kW) and arc current (120–220 A). The outlet region for the plasma jet extends to 20 cm downstream of the exit nozzle. Fluid dynamic and thermal characteristics together with diffusion of argon, hydrogen and oxygen species, and distribution of plasma species in the discharge and the plasma jet are obtained for currents from 120 to 220 A. The results of the calculations show that the plasma jet exhibits high spatiotemporal fluctuations in the shear layer between the plasma jet and colder steam atmosphere. The most abundant species in the plasma jet are hydrogen and oxygen atoms near the jet center, and molecules of H2, O2 and OH in colder surrounding regions. Satisfactory agreement is obtained with measurements of the radial temperature and electron number density profiles near the jet center close to the nozzle exit.

Comparative Study of Plasma Torch Characteristics Using Air and Carbon Dioxide

The plasma torch is the key component of the thermal plasma-assisted material processing system. Particularly, direct current (dc) nontransferred arc plasma torch is widely used in high-temperature material processing applications. The characteristics of the thermal plasma jet emanating from the plasma torch depend on many factors, including arc current, type of plasma forming gas, gas flow rates, gas injection configuration, torch geometry, and so on. This experimental study focuses on the comparison between the effects of CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and air on the arc voltage, electrothermal efficiency, and specific enthalpy of the plasma torch operated at the atmospheric pressure. For this purpose, a low-power dc plasma torch consisting of a rod-type thoriated tungsten cathode and the copper anode was customized. CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and air were used as the plasma forming gases along with a feeble amount of argon (15 lpm). The plasma torch was operated over a wide range of current (100–175 A) with fixed gas flow rates. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula> characteristics and the electrothermal efficiency of the plasma torch were measured, and results were compared. The maximum electrothermal efficiency and specific enthalpy of the plasma torch when operated with CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> were reported as 70% and 1900 KJ/Kg, respectively, which is higher than the same torch operated with air as the plasma forming gas. The electron number density and electron temperature of the air and CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> plasma jet were measured by optical emission spectroscopy (OES). The calculated electron number density and electron temperature of the plasma jet with CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> were <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.89\times 10\,\,^{\mathrm{ 16}}$ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> and 8598 K, respectively, which is higher than air plasma jet. It was found that CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has a stronger influence than air on the arc voltage fluctuation, electrothermal efficiency, and operating regime of the plasma torch.

Evaluation of Evaporative Degradation of Arc Torch Cathodes in Hydrocarbon-Containing Plasmas for Spraying, Thermal Protection Testing and Related Technologies

Design of non-transferred DC electric arc plasma torches (EAPTs) operated with plasma gases containing alkane hydrocarbons, as a promising type of heaters for a number of technologies (thermal spraying, surface hardening, testing of thermal protection systems, etc.), requires taking into account the evaporation rate of surface cathode material (as one of the channels of its ablative degradation). For this procedure, as the first stage, thermodynamic methods can be used to simulate the composition and properties of reactive C–H–O–N–Ar–Me-systems with variable set of such input parameters as the ratio of components of plasma-forming mixture, its pressure and temperature. We theoretically estimated the evaporative degradation of the material for three variants of EAPT cathode with alkane-containing plasmas (“hot” thermochemical zirconium and thermionic tungsten, and “cold” copper) in equilibrium and quasi-equilibrium modes of “plasma gas + surface cathode material”-mixture, with use of generalized thermodynamic properties of the materials. The calculation for conditions with pressure, which is characteristic for EAPT discharge chamber, showed that when varying the initial composition of the plasma-forming mixture (from oxidizers (air or combustion products of alkanes) to reducing gases based on the products of combined partial oxidation and pyrolysis of alkanes), the effect of a difference in the cathode evaporation rate EAI was observed in systems based on (air + alkane)-mixtures near the melting point of surface cathode substances, in a comparison with the case of EAPTs with more conventional gases (commercial N2, air) and, importantly, for two variants of the analyzed cathodes (with the exception of copper). In addition, the electrode erosion value was compared for simulated zirconium cathode (in terms of erosion evaporative component) when operating on the combustion products of alkanes from “air + CH4”-mixture, and for some known EAPTs with similar cathodes in other gases. Using the case of earlier tested DC plasma torch with rod Zr-cathode (with microheterogeneous surface) as an example, it was found that our calculation indicates non-monotonic dynamics of EAI value and fractions of Zr-containing vapors as a result of the change of the fuel-air equivalence ratio f of initial reactive mixture. This effect is inconsistent with measured cathode composition, which shows a probability of nonequilibrium character of thermal and diffusion processes in near-electrode plasma and surface layer (~1 mm) of the electrode, at least in the modes with arc current in the torch near 300 A. Besides this, it should be noted that obtained modeling data on the behavior of zirconium compounds (ZrO2, ZrC) in C–H–O–N–Ar–Zr-system can be used not only for improvement of the torch cathodes, but also for design of new Zr-containing thermal protection systems to predict preliminary their ablation rate in a flow of products of combustion (including incomplete one) of engine-, rocket- and other fuels. Similarly, the results on the copper compounds behavior near the metal evaporation temperature can be useful for optimizing the process of plasma spraying of copper alloy coatings.

Modelling of Electric Processes in Circuits of Arc Plasma Torches Part 1. Approximations of Static Characteristics of Arc Plasma Torches

The article discusses selected structural and operational properties of DC and AC arc plasma torches. References cited in the article contain generalised analytical expressions identifying experimental current-voltage characteristics of typical arc plasma torches. Values of coefficients in formulas approximating static current-voltage characteristics depend not only on the type and the polarity of the plasma torch but also on values of criterial factors. The study discusses separately DC plasma torches and single-phase AC plasma torches.

Application of functional coatings by supersonic thermal plasma flows

Development of modern high-speed technologies for thermal spraying proves that deposition of high-quality dense coatings requires velocity of sprayed particles to be 600 m/s and above. Plasma spraying is the most versatile and highly productive deposition method of various functional coatings without any limitations on the melting points of the sprayed materials. Present work describes a DC plasma torch designed for operation in a supersonic mode. The supersonic plasma torch features de Laval nozzle, utilization of air as a plasma-forming gas, and annular injection unit for delivery of the powder to the plasma jet. The comparison of NiCr and NiAl coatings deposited both in subsonic and supersonic modes are presented. Methods for further increasing the sprayed particles’velocity and the requirements for their heating temperature are proposed.

Non-equilibrium modeling on the plasma–electrode interaction in an argon DC plasma torch

A 2D two-temperature chemical non-equilibrium model considering both cathode and anode space-charge sheath is applied to investigate the plasma–electrode interaction in a laminar argon DC plasma torch working at atmospheric pressure. In order to validate the model, the predicted arc voltage is compared with experimental values under different working conditions, and a reasonable agreement is obtained. The distributions of arc characteristics in the plasma column and electrode regions of a DC arc plasma torch are analyzed in detail. Moreover, the effects of thoriated tungsten, pure tungsten and non-uniform thoriated tungsten cathodes on the plasma characteristics inside the DC plasma torch are investigated. It is found that a constricted arc attachment with the highest current density is obtained at the non-uniform cathode, leading to the largest velocity and electric potential drop in the plasma column. The pure tungsten cathode produces the highest temperatures and heat flux along the cathode surface, which is caused by the largest arc voltage and intense space-charge sheath heating. The temperature and heat flux density on the thoriated tungsten cathode are the lowest, leading to a diffuse distribution of current density. The results indicate that the different cathodes can exert an important influence upon the plasma behavior near the cathode. Furthermore, the torch exit parameters are also slightly different due to their different arc voltages and overall input power.