Two-Temperature Chemical Non-equilibrium Modeling of Argon DC Arc Plasma Torch
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Two‑Temperature Chemical Non‑equilibrium Modeling of Argon DC Arc Plasma Torch Jiang‑Hong Sun1 · Su‑Rong Sun1 · Li‑Hui Zhang1 · Hai‑Xing Wang1,2 Received: 8 May 2020 / Accepted: 13 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract A 2D two-temperature chemical non-equilibrium model has been developed to investigate the plasma characteristics inside a DC arc plasma torch of argon. In this study the chemical kinetic model is carefully examined in order to properly capture the spatial variations of plasma characteristics, especially near the electrodes and arc fringe, where large gradients of plasma parameters exist. Two different sets of chemical kinetic processes are adopted in the calculation. The first chemical kinetic model [model (a)] includes the ground-state argon atoms, excited argon 4s state, atomic ions, molecular ions, and electrons, while the second model [model (b)] only considers the ground-state argon atoms, excited argon 4s state, atomic ions, and electrons. The predicted exit temperature and arc voltage by model (a) are in better agreement with experimental measurements. A delayed anode attachment with a higher arc voltage occurs in model (a) due to the low electron density in the upstream region of arc-anode attachment. Compared with the wide arc-anode attachment zone of model (b), model (a) exhibits a more constricted anode arc root with higher current density, which leads to a higher heat flux and temperature on the anode. This phenomenon may be explained by the rapid loss of electrons outside the arc-anode attachment zone due to the dissociative recombination of argon molecular ions. Moreover, model (a) produces a longer arc column with slightly higher maximum temperature and velocity on the axis, which is caused by its larger input energy. Keywords Plasma torch · Chemical non-equilibrium model · Argon arc
Introduction The DC plasma torches have been widely used in many industrial applications [1], due to its relatively simple structure and ability to generate thermal plasmas with high temperature and high heat flux. The arc behavior inside the DC plasma torch is of vital importance, * Su‑Rong Sun [email protected] Hai‑Xing Wang [email protected] 1
School of Astronautics, Beihang University, 100191 Beijing, China
2
Ningbo Institute of Technology, Beihang University, 315800 Ningbo, China
13
Vol.:(0123456789)
Plasma Chemistry and Plasma Processing
however, the direct measurements inside the torch can be very difficult [2]. Therefore, the numerical modelling is commonly carried out to provide the plasma characteristics and many modeling results are available in the literature [2–4]. The reasonable physical and chemical model is particularly crucial for the numerical modeling of the plasma torch. The local thermal equilibrium assumption was widely used in early literature [5–8], which can successfully predict the plasma properties of the arc column. However, the equilibrium assumption should be carefully examined due to the non-equilibrium phenomena
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