普通大气等离子喷涂过程的数值分析

Numerical Analysis on Atmospheric Plasma Spray Process

根据普通大气等离子喷涂的喷枪尺寸和喷枪结构沿轴线对称的特点,建立了包含阴、阳固体电极的扇形计算区,用于分析等离子体的流动特性。运用非局域热平衡方法对电子和重粒子的温度区别对待,并且考虑了等离子气体在喷枪内的电离与复合反应,得出了普通等离子喷涂在纯氩和氩氢混合气氛中的等离子气流温度、速度场分布,以及喷枪喉部尺寸变化对气流的影响。模拟结果表明:在加入氢气之后,喷涂温度、气体电离度和内部气流速度均显著提高;随喉部直径减小等离子气流速度不断提高,最后达到超声速水平,而温度则随着喉部直径的减小而降低,在喉部直径减小到一定程度后温度的变化趋缓。

A three-dimensional model is set up to analyze the plasma flow characters. Ignoring powder injector, the spray gun gets axisymmetric, so a fan-shaped calculating domain including electrodes is sufficient. The non-local thermal equilibrium is considered to investigate the plasma flow, and the ionization and recombination reactions are taken into account. The contours of temperature and velocity are displayed under argon and argon-hydrogen working conditions. Moreover, the influence of gun throat diameter on plasma flow is discussed. The results show that gas temperature, degree of ionization and internal velocity are significantly improved after adding hydrogen~ with the gun throat diameter decreasing, velocity of plasma jet increases continually and finally reaches to a supersonic level, while temperature lowers and changes slowly as the throat diameter decreases to a certain size.