等离子体炬电弧放电热膨胀不稳定性分析

Analysis of Thermal Expansion Instability in Plasma Torch Arc Discharge

针对层流电弧中的不稳定性以及电弧脉动的起因,利用简化的一维放电模型,分析了稳态放电非转移弧层流等离子体射流的放电热膨胀不稳定性表现为射流周期性震荡的宏观性质,提出电弧放电室进气流初始定向流速增加能够抑制等离子体炬射流放电不稳定性的发展。放电热膨胀不稳定性发生的主要机制是:由于放电气体密度的随机涨落与电场加热气体功率的反相关变化,导致电弧放电通道内温度高的区域随着加热功率的增加而正反馈增加,由此导致电弧放电热膨胀不稳定;放电气体的定向流速度为射流增加的一项动压与密度变化成正比,导致放电热膨胀不稳定性的发展具有阈值限制;增加定向流速度能够抑制放电热膨胀不稳定性。

The thermal expansion instability of arc discharge was theoretically analyzed by a 1D cylinder arc discharge model. Thermal expansion instability of arc discharge caused by the electric heating power was proportional to gas density fluctuation. Heating could increase the total pressure in the lower density region and thus the low density region became denser. With the flow of two regions to the outlet, the jet beam velocity and temperature would fluctuate due to the thermal expansion instability. The inlet velocity of an arc discharge gas could help to stabilize the thermal expansion instability. The total pressure of a fluid gas includes the dynamic pressure which is proportional to gas density. The fluctuation of a gas density would decrease with the increase the electric heating power and thermal pressure. So decrease the dynamic pressure could help to keep the total pressure in balance. The discharge thermal expansion instability could be compressed by increasing the inlet fluid velocity over a critical value.