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Ar-O2混合气体电弧的数值模拟

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## Numerical simulation of mixture gas arc of Ar-O2

Wang Xin-Xin, Chi Lu-Xin, Wu Guang-Feng, Li Chun-Tian, Fan Ding
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• #### 摘要

混合气体电弧被广泛地应用于焊接制造领域, 为了深入理解混合气体电弧的传热和传质特性, 本文建立了Ar-O2混合气体电弧的二维稳态数学模型. 模型基于局域热平衡假设, 混合气体电弧的热力学参数和输运系数是温度和氧浓度的函数, 分别采用组合普通扩散系数和组合温度扩散系数描述氧和氩两种组分之间的扩散行为, 研究了不同电流条件下的氧分布及其对电弧温度场和流场的影响. 结果表明, 对于Ar-5%O2的混合气体电弧, 氧在电弧中呈现极不均匀的分布, 在电弧中心轴线附近和靠近两极的区域, 氧浓度高于混合气体浓度, 而在其他区域则明显小于混合气体浓度. 在小电流时, 氧集中分布于阴极和阳极附近, 且在阴极附近出现峰值; 而在大电流时, 氧的分布明显向阳极集中, 且在阳极中心附近出现峰值. 两种情形下, 氧在距离阳极表面0.1 mm的区域分布都不均匀. 与纯Ar保护相比, 混入5%的O2使电弧出现一定程度的收缩, 温度和等离子体流速升高.

#### Abstract

Mixture gas arcs are used extensively in welding manufacturing. A two-dimensional steady mathematical model for Ar-O2 mixture gas arc is developed to understand further the heat and mass transfer of the mixture gas arc. The model is based on the assumption of local thermodynamic equilibrium, and the thermodynamic parameters and transport coefficients are dependent on both the temperature and the oxygen content. In the present model, the diffusion between the argon species and oxygen species is depicted by the approach of the combined diffusion coefficient, i. e. the mixture gas arc is simplified into two different species, and the diffusion between them is formulated by combined ordinary diffusion coefficient and combined temperature diffusion coefficient; the oxygen distribution and its influence on the temperature and flow field of the arc are investigated for two different current conditions. It is shown that the oxygen species presents significant non-uniform distribution for argon gas mixed with 5% oxygen; the oxygen content is higher than that in mixed shielding gas in the regions close to the electrodes and arc axis, while its content is lower than that of the mixed shielding gas in other regions. For high current, oxygen concentrates more to the flat anode, while it concentrates more to tungsten cathode for low current. For both cases, oxygen content is inhomogeneous in the region 0.1 mm above the anode. The 5% oxygen mixed in argon constricts the arc plasma to some extent and thus raises the arc temperature as well as the plasma flow velocity.

#### 作者及机构信息

###### 通信作者: 王新鑫, wang@cqut.edu.cn
• 基金项目: 国家自然科学基金(批准号: 51705054)和重庆市教委科学技术研究计划(批准号: KJ1600903, KJ1709197)资助的课题.

#### Authors and contacts

###### Corresponding author: Wang Xin-Xin, wang@cqut.edu.cn
• Funds: Project supported by the National Natural Science Foundation of China (Grant No. 51705054) and the the Scientific and Technological Research Program of Chongqing Municipal Education Commission, China (Grant Nos. KJ1600903, KJ1709197).

#### 施引文献

• 图 1  扩散系数　(a) 组合普通扩散系数$\overline {D_{{\rm{Ar,}}{{\rm{O}}_{\rm{2}}}}^x}$; (b) 组合温度扩散系数$\overline {D_{{\rm{Ar,}}{{\rm{O}}_{\rm{2}}}}^T}$

Fig. 1.  Diffusion coefficients: (a) Combined ordinary diffusion coefficient$\overline {D_{{\rm{Ar,}}{{\rm{O}}_{\rm{2}}}}^x}$; (b) combined temperature diffusion coefficient$\overline {D_{{\rm{Ar,}}{{\rm{O}}_{\rm{2}}}}^T}$

图 2  求解域示意图

Fig. 2.  Schematic of the computation domain.

图 3  混合气体电弧的温度场和氧组分质量分数分布 (a) 200 A; (b) 80 A

Fig. 3.  Temperature field and oxygen mass fraction of Ar-O2 mixture gas arc for different current: (a) 200 A; (b) 80 A

图 4  距离钨极尖端不同位置氧组分质量分数的径向分布　(a) 200 A; (b) 80 A

Fig. 4.  Radial distributions of the mass fraction of oxygen at different distances below the cathode: (a) 200 A; (b) 80 A.

图 5  混合气体电弧的流场　(a) 200 A; (b) 80 A

Fig. 5.  Flow fiels of mixture gas arc：(a) 200 A; (b) 80 A.

图 6  混合气体电弧阳极表面0.1 mm处氧组分的分布

Fig. 6.  Oxygen mass fraction of mixture gas arc 0.1 mm above the anode.

图 7  氧组分对电弧温度场的影响　(a) 200 A; (b) 80 A

Fig. 7.  Effect of oxygen on the arc temperature field: (a) 200 A; (b) 80 A.

图 8  氧组分对电弧流场的影响　(a) 200 A; (b) 80 A

Fig. 8.  Effect of oxygen on the arc flow field: (a) 200 A; (b) 80 A.

图 9  200 A电流TIG电弧的温度场对比

Fig. 9.  Comparison of the calculated temperature fiels of TIG arc for 200 A current.

图 10  距离阴极尖端不同位置氧组分径向分布的计算结果对比　(a) Murphy的结果[40]; (b) 本文的结果

Fig. 10.  Comparison of radial distribution of oxygen calculated at different distances below the cathode: (a) Murphy’s results[40]; (b) the present model’s results.