The Effects of Cold Gas Injection on a Confined Arc Column

This paper considers the interaction of a thermal argon arc plasma confined in a relatively long water-cooled cylindrical tube with a cold argon flow injected radially into the tube through a circumferential slit. An analytical model is established to predict the thermal, the fluiddynamic, as well as the electrical behavior, of such an arc assuming laminar flow and Local Thermodynamic Equilibrium (LTE) of the arc plasma. Numerical solutions for the field variables are obtained by solving simultaneously the mass, momentum, energy, and charge conservation equations by an iterative finite difference method. The results show that the arc column becomes constricted at the location of gas injection due to thermal and fluiddynamic effects associated with the injected cold flow. The arc responds to the constriction by an increase of the temperature in the core region which resists the penetration of the cold flow into the arc. This penetration remains relatively small even at high injection ratios because the arc temperature and, therefore, the resistance to flow penetration increases with increasing injection ratio. The enhanced Joule heating in the injection region leads to a minor thermal expansion of the base flow which can be observed upstream of the injection slit. This effect becomes less pronounced as the injection mass flow rate increases.