3D computational study of arc splitting during power interruption: the influence of metal vapor enhanced radiation on arc dynamics

Plasma–solid interaction represents a major concern in many applications such as power-interruption and plasma–metal processing. Characterized by high-current density and voltage drop, the arc roots dissipate intensive heat to electrode vaporization, which participates in the ionization and, thereby, significantly alters the plasma properties and gas dynamics. Most of the arc root models feature approaches based on surface temperature or (temperature dependent) current density. Due to the complexity of conjugated heat transfer across arc roots involving three-phase interactions of plasma with liquid spots and solid electrodes, accurately determining the surface temperature distribution is extremely computationally demanding. Hence, models hitherto fail to quantitatively estimate neither the molten spot size nor the total amount of vaporization. In this work, we propose an arc root model featuring a hemispherical structure that correlates the molten spot size with the heat partition between conduction and vaporization to estimate the energy dissipation at arc roots and, thus, to trace the vaporization rate. Following local partial pressure adjusted Langmuir vaporization, we deduce an analytical solution of molten spot size for quasi-steady-state, which compares favorably with experiments. Specifically, the vaporization dominates over conduction for large molten spots as in the case of high-current arcs. However, for low-current arcs, the vaporization heat is trivial compared with conduction. Furthermore, we integrate this arc root model into a study case of arc plasma based on the magnetohydrodynamics method. The simulated arc voltage and arc displacement match with the experiment. This model is expected to find broad applications in power interruption and plasma etching.

Development of an arc root model for studying the electrode vaporization and its influence on arc dynamics

Arc erosion behavior and mechanism of Ag/Ti3SiC2 cathodes in different atmospheres

The ultrasonic vibration assisted plasma arc welding process was developed to enhance the welding efficiency while the underlying mechanism of ultrasonic interaction with plasma arc is not yet elucidated. In this study, a numerical model of ultrasonic vibration assisted plasma arc is proposed, which takes into account the influence of plasma flow velocity on the ultrasonic propagation as well as the macro- and micro-effects of ultrasound on the heat-pressure characteristics of the plasma arc. The calculation results show that the plasma flow velocity affects the ultrasonic field in the plasma arc, resulting in a significant increase in the sound pressure near the workpiece surface. Ultrasound can increase the thermal conductivity of plasma and reduce the electric conductivity of plasma. The acoustic radiation force is at the same order of electromagnetic force, while the acoustic energy is five orders of magnitude lower than Joule heat. Under the comprehensive action of ultrasonic vibration, the plasma arc pressure and current density on the anode surface are increased so that the keyholing/penetrating ability of the plasma arc is enhanced. The model is validated by comparison of predicted and measured arc pressure and current density on the anode surface.

Numerical analysis of the heat-pressure characteristics in ultrasonic vibration assisted plasma arc

A 2D two-temperature chemical non-equilibrium model considering the space-charge sheath is established to investigate the plasma-electrode interaction in an 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 electrodes regions of DC arc plasma torch are analyzed in detail. Moreover, the effects of different types of cathodes on the plasma characteristics inside the DC plasma torch are investigated. Three different types of cathodes are considered in this study, including thoriated tungsten, pure tungsten and non-uniform thoriated tungsten cathodes. 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 thoriated tungsten cathode are the lowest, leading to the diffuse distribution of current density. The results indicate that the different cathodes can exert an important influence upon the plasma behaviors near the cathode, while the torch exit parameters have been less affected, which are determined by the overall input power.

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

Investigation of erosion mechanism of tungsten-based cathode in Ar-N2 DC arc

Cathode erosion is an important issue in the industrial applications of the direct-current arc. However, the mechanism of erosion under molecular gas has not been well clarified. The purpose of this study is to elucidate the erosion mechanism of tungsten-based cathodes in atmospheric pressure Ar-N2 DC arcs. Tungsten electrodes doped with various metal oxides as electron emitters were investigated. The metal vapor from the cathode was successfully visualized by an optical system that combined a high-speed camera with bandpass filters. The difference in the electrode temperature distribution due to the additives is explained with two factors. The first is the thermal factor that the high melting point additive is difficult to spread on the cathode surface. The second is the chemical factor that the emitter is reduced by nitrogen radicals. Advances in the understanding of such electrode phenomena are expected to lead to expanded applications of nitrogen arcs.

https://iopscience.iop.org/article/10.35848/1347-4065/abbd7d/pdf

Investigation of electrode erosion mechanism in Ar-N2 DC arc based on visualization of electrode phenomena

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Investigation of erosion mechanism of tungsten-based cathode in Ar-N2 DC arc

Investigation of electrode erosion mechanism in Ar-N2 DC arc based on visualization of electrode phenomena