Zhuojin Pipe Fitting Co., LtdDual-Temperature Numerical Simulation of TIG Arc Plasma
Literature Overview
This study by Huang Yong and colleagues from the State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals at Lanzhou University of Technology presents a two-dimensional axisymmetric dual-temperature mathematical model for TIG arc plasma. Published in the Welding Journal in 2018, the work is supported by the National Natural Science Foundation of China (Project 51265029) and addresses a fundamental gap in arc physics modeling by decoupling electron temperature from heavy-particle temperature to capture non-equilibrium phenomena within the plasma column.
Core Technical Content
The model is built upon the continuity equation, momentum conservation equation, electron energy conservation equation, heavy-particle energy conservation equation, and Maxwell's equations. All thermodynamic properties and transport coefficients of the plasma are treated as functions of both electron temperature (Te) and heavy-particle temperature (Th), rather than assuming a single equilibrium temperature. The model is solved using FLUENT computational fluid dynamics software, yielding comprehensive fields including electron temperature distribution, heavy-particle temperature distribution, pressure field, velocity field, and electric potential field.
The key finding is that the TIG arc exhibits a typical bell-shaped geometry. At the arc center, heavy-particle temperature and electron temperature are nearly identical throughout, indicating local thermodynamic equilibrium (LTE) in this region. However, at the arc periphery and near the anode surface, significant divergence between Te and Th is observed, demonstrating pronounced non-equilibrium behavior. This spatial variation in equilibrium state has direct implications for how arc energy is deposited onto the workpiece surface.
Technical Points and Engineering Relevance
The dual-temperature approach is particularly important for understanding arc behavior under conditions where LTE assumptions break down. In standard single-temperature models, the arc is assumed to be in local thermodynamic equilibrium everywhere, which simplifies calculations but masks critical non-equilibrium effects that govern heat transfer at the arc boundaries.
| Parameter | Arc Center | Arc Periphery / Anode Surface |
|---|---|---|
| Te vs Th | Nearly equal (LTE) | Significant difference (non-equilibrium) |
| Equilibrium State | Local thermodynamic equilibrium | Non-equilibrium |
| Physical Consequence | Predictable energy transfer | Complex heat flux distribution |
| Modeling Requirement | Single-temperature sufficient | Dual-temperature essential |
For engineers working with TIG welding of thick-section pipelines or high-temperature alloys, understanding where non-equilibrium occurs within the arc helps explain why simple heat source models sometimes fail to predict weld geometry accurately, especially near the fusion boundary. The non-equilibrium region at the arc edge is precisely where the energy flux transitions from the dense plasma core to the cooler workpiece, and the temperature disparity affects the local heat input rate and penetration characteristics.
Study Insights
The significance of this work extends beyond academic interest. In pipeline welding applications involving thick-walled carbon steel or alloy steel girth welds, the accuracy of heat source modeling directly influences the prediction of weld geometry, residual stress distribution, and the extent of the heat-affected zone. The non-equilibrium effects identified at the arc periphery suggest that conventional Gaussian or double-ellipsoidal heat source models may need refinement for critical applications where precise prediction of HAZ width and microstructural transformation is required.