Enthalpy Probe Measurements on Thermal Plasma Jets Generated by a Hollow Electrodes Plasma Torch with Reversed Polarity Discharge

Abstract

Summary form only given. A reversed polarity discharge of the thermal plasma torch is frequently used in the material processing field, because a turbulent flow of the plasma jet significantly enhances the mixing of reactants with the plasma due to an active motion of cathodic arc roots at the outlet of the torch. Furthermore, an eroded cathode which protrudes from the plasma torch exit is conveniently replaced with a new one for the reverse polarity plasma torch. Using a hollow electrodes plasma torch with a reverse polarity operated, nanostructured carbonaceous materials were synthesized by the thermal decomposition of methane, and different morphologies of them were observed depending on the input electric power. Since the input power level of the plasma torch strongly affects temperature and velocity distributions of the thermal plasma jet, a study on the characteristics of the jets is required to understand the synthesis mechanism of carbonaceous materials. In spite of numerous research on the reverse polarity plasma torch, only limited knowledge has been so far established on the characteristics of thermal plasma jets generated by it. Through the present experimental work, a previous two-dimensional numerical model is modified more accurately to predict the thermal flow characteristics of plasma jets produced by reversed polarity discharges of a hollow electrodes plasma torch in various operating conditions. For confirming the validity of the numerical model, the temperature and velocity distributions of thermal plasma jets ejected from the torch are measured by using an enthalpy probe diagnostic method. In this experimental work, a hollow cathode with 16 mm diameters is employed and several tens kW power is supplied to the plasma torch