The cascaded-anode plasma torch makes it possible to get a longer and more stable plasma jet with higher specific enthalpy than conventional plasma torches. It is now used widely, but there are still few models of the cascaded-anode plasma torch. This study developed a 3-D time-dependent model that couples the gas phase and electrodes by encompassing the electromagnetic and heat equations both in the electrodes and gas phase. The model was applied to a commercial plasma spray gun equipped with a single cathode, single cylindrical anode and an inter-electrode insert to fix the average arc length. This paper examines the effect of the boundary conditions for the magnetic vector potential and electric current density on the electromagnetic, velocity and temperature fields of the plasma jet. The model predictions showed that, for such plasma torches where the arc is close to walls, the Biot and Savart formalism is required at the domain boundaries for the magnetic vector potential. They also showed that similar plasma fields could be obtained by imposing an electric current density profile at the cathode tip or by including the electrodes in the computational domain. However, this profile has to be chosen according to the specific design of the cathode, which is not obvious when the cathode has a design different from that of conventional plasma torches with sharp conical tip or rounded tip.

中文翻译：

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电磁边界条件对等离子炬模型可靠性的影响

与传统等离子炬相比，级联阳极等离子炬可以获得更长、更稳定的等离子射流，其比焓更高。它现在被广泛使用，但级联阳极等离子炬的型号仍然很少。该研究开发了一个 3-D 时间相关模型，该模型通过包含电极和气相中的电磁和热方程来耦合气相和电极。该模型应用于配备有单个阴极、单个圆柱形阳极和用于固定平均弧长的电极间插入件的商用等离子喷枪。本文研究了磁矢量势和电流密度的边界条件对等离子体射流的电磁场、速度场和温度场的影响。模型预测表明，对于这种电弧靠近壁的等离子炬，在磁矢量势的域边界处需要 Biot 和 Savart 形式主义。他们还表明，通过在阴极尖端施加电流密度分布或将电极包括在计算域中，可以获得类似的等离子体场。然而，必须根据阴极的具体设计来选择该轮廓，当阴极的设计不同于具有尖锐锥形尖端或圆形尖端的常规等离子体炬的设计时，这一点并不明显。他们还表明，通过在阴极尖端施加电流密度分布或将电极包括在计算域中，可以获得类似的等离子体场。然而，必须根据阴极的具体设计来选择该轮廓，当阴极的设计不同于具有尖锐锥形尖端或圆形尖端的常规等离子体炬的设计时，这一点并不明显。他们还表明，通过在阴极尖端施加电流密度分布或将电极包括在计算域中，可以获得类似的等离子体场。然而，必须根据阴极的具体设计来选择该轮廓，当阴极的设计不同于具有尖锐锥形尖端或圆形尖端的常规等离子体炬的设计时，这一点并不明显。