Numerical design study on a high-powered segmented-type arc plasma torch for a high-enthalpy supersonic plasma wind tunnel

Abstract

As a high-powered plasma source to produce a specific enthalpy higher than 20 MJ/kg at an air flow rate of 50 g/s for a supersonic plasma wind tunnel, a segmented-type arc plasma torch with an input power level of MW class is characterized in this paper. For this purpose, a numerical parametric study was carried out to determine the main design parameters, such as, the constrictor length LC, the diameter of segmented disk DC, and the diameter of the electrode DE, under the requirements of specific enthalpy and air flow rate. From the results of the numerical study, firstly the plasma power and specific enthalpy are found to increase with increasing LC at the expense of the torch efficiency, which is defined as the ratio of the total exit enthalpy to the plasma power. On the other hand, an increase in DC is observed to improve the torch efficiency by reducing the plasma power at a fixed arc current and gas flow rate. Moreover, an increase in DE is also found to contribute to improvements in the torch efficiency and the specific enthalpy by expanding the high-temperature region of the arc plasma and decreasing plasma velocities at the torch exit. Accordingly, a scale up to MW class for obtaining a high specific enthalpy can be achieved efficiently by inserting segmented disks with relatively large diameters between enlarged electrodes and then increasing the arc currents. For example, if the length of a constrictor consisting of segmented disks with a diameter of DC = 25 mm is extended to LC = 900 mm and then the arc current is increased up to 800 A, it is predicted that a specific enthalpy of 21.2 MJ/kg can be achieved at a plasma power of 2.89 MW and an air flow rate of 50 g/s, which corresponds to a torch efficiency of 36.6%. Based on these numerical parametric study results, we expect that a segmented arc plasma torch can be designed to meet the requirements of a supersonic plasma wind tunnel, such as a specific enthalpy, air flow rate and plasma power.