氩氢摩尔比对直流电弧等离子体喷射法等离子体放电特征影响的计算

Calculation of the influence of argon-to-hydrogen mole ratio on the discharge characteristics of plasma in DC arc plasma jet

假定氩-氢等离子体处于局部热力学平衡状态,利用理想气体分子运动论和经典查普曼-恩斯科格(ChapmanEnskog)方法,在获取符合直流电弧等离子体喷射法实际工况的等离子体热力学和输运参数的基础上,基于FLUENT软件进行二次开发,添加电磁场相关的电流连续方程、安培定律等方程及洛伦兹力、焦耳热等源项,模拟研究氩氢摩尔比对等离子体放电特征影响规律.结果表明:在气压为8 k Pa,工作电流150 A,氩氢摩尔比由3∶1降至1∶3时,等离子体最大流速由829 m·s-1增至1127 m·s-1,最高温度由20600 K逐渐降低至16800 K,电弧对基体的加热能力逐渐增强的同时使基体表面温度均匀性变差.在其他条件不变的前提下,氩氢摩尔比为1∶2时能获得适宜金刚石生长且相对均匀的基体表面温度.

The effect of argon-to-hydrogen mole ratio on the discharging behavior of argon-hydrogen plasma was simulated and studied on the assumption that argon-hydrogen plasma is in a local thermodynamic equilibrium. The kinetic theory of ideal gases and the classical Chapman-Enskog method were employed in the study. The plasma thermodynamic and transport parameters consistent with the actual condition of the DC arc plasma jet method were firstly found, and secondary development was made on FLUENT software platform. Equations, like current continuum and Ampere＇s law, and source items, like Lorentz force and Joule heat, which are associated with electromagnetic fields were also taken into account. The results show that when the gas pressure and operating cur- rent are 8 kPa and 150 A, respectively, and the argon-to-hydrogen mole ratio changes from 3：1 to 1 ： 3, the maximum flow rate of plas- ma increases from 829 to 1127 m.s-1, the maximum temperature falls from 20600 K to 16800 K, and the heating capacity of the DC arc improves while the substrate surface temperature uniformity deteriorates. Under the other conditions being unchanged, when the argon-to- hydrogen ratio is 1： 2, a relatively uniform and proper substrate surface temperature can be obtained for the growth of diamond films.