Numerical studies on the effects of operating parameters on the behaviour of transferred arc inside the crucible with gas injection through the cathode at different operating pressures

Abstract

Hollow cathode with gas injection in transferred arc plasma system has been used for high temperature material processes. The effect of operating parameters such as gas flow rate, electrode gap, arc current, etc on the arc behaviour at an operating pressure of 1 atm is studied numerically. The knowledge on the arc behaviour at operating pressures lower and higher than atmospheric pressure is very limited. In this work, a two dimensional axi-symmetric model is developed to simulate the behaviour of the argon arcs formed between hollow cathode with gas injection and crucible anode as well as heat transfer from the plasma to the anode at different operating pressures. The effects of gas flow rate and electrode gap on the arc behaviour and heating efficiency at different operating pressures are investigated. The arc voltage is strongly influenced by both operating pressure and electrode gap. The effect gas flow rate on the arc voltage is stronger at higher operating pressures. The movement or detachment of the arc root from the centre of the anode is strongly influenced by operating pressure and gas flow rate. Arcs formed at 0.2 atm have unique features compared to the arcs formed at higher operating pressures. The heat flux to the anode is higher where arc root is attached and the highest arc heating efficiency of 68.1% is predicted at an operating pressure of 0.2 atm, electrode gap of 15 mm and gas flow rate of 5 lpm.