Properties of hybrid water/argon DC arc torch under reduced pressure

Abstract

Summary form only given, as follows. Hybrid plasma torch is based on a combination of principles of classical gas-stabilized dc arc torch and water-stabilized torch. High enthalpy thermal plasma jet is generated in the torch that is utilized for plasma processing applications like plasma spraying or waste treatment. The torch was attached to the low-pressure chamber and characteristics of the torch and properties of plasma jet were investigated for the pressure range of 10 to 100 kPa. Under these slightly reduced pressures the jet remains subsonic, but both the torch characteristics and plasma jet properties axe substantially changed Pressure inside the arc chamber is reduced as a consequence of reduction of ambient pressure. The boiling point of water is thus decreased and higher evaporation rate from water vortex surrounding the arc column results in increase of an arc cooling intensity of arc column and a rate of absorption of radiation in the vapor sheath surrounding the arc. Consequently the arc voltage, arc power and plasma torch efficiency are increased. Plasma jet properties downstream of the torch nozzle exit were investigated. The fluctuations of emitted light were recorded The intensity of emitted light is substantially reduced due to pressure decrease. This is related not only to a reduction of plasma density but also to a decrease of plasma temperature due to higher evaporation rate in the arc chamber. Characteristic frequency of plasma flow fluctuations as well as phase velocity of propagation of hydrodynamic instability along the jet were substantially increased due to pressure reduction as a consequence of increase of plasma flow velocity in the jet. The results of experiments are analyzed on the basis of simple theoretical model of arc with hybrid stabilization.