Parametric study of a vortex-enhanced supersonic inductively coupled plasma torch

Radio-Frequency (RF) Inductively Coupled Plasma (ICP) torches have applications ranging from electric space propulsion to materials processing and gas conversion. In this work, we investigate a novel supersonic RF ICP torch design with a bidirectional gas vortex configuration, which forms a flow field of two counter propagating vortices that significantly enhance gas heating and thermal efficiency. By using indirect diagnostic measurements which include optical emission spectroscopy, calorimetry and electrical measurements, the effect of the nozzle diameter on electron density, gas temperature and performance metrics such as thermal efficiency and specific enthalpy are explored. Experiments are performed on nozzle throat diameters ranging from 1.5 to 4.0 mm with powers, gas pressures and argon mas flow rates between 200 – 1000 W, 5 – 80 kPa and 0 – 400 mg/s respectively. Depending on operating conditions the electron densities and excitation temperatures range from 10^20 to 10^21 and 6000 - 9500 K, with the 1.5 mm nozzle experiencing the highest density and excitation temperature for a set mass flow rate and power. However, the 1.5 mm nozzle obtains a maximum thermal efficiency of only 29% at a specific enthalpy of 1.5 MJ/kg, in contrast to the 4.0 mm nozzle which reaches a maximum thermal efficiency of 70% and a specific enthalpy of 1.3 MJ/kg. The increase in thermal efficiency with increasing nozzle diameter is due to decreasing conductive heat loses to the torch walls leading to an increased temperature at a given pressure. Results show a significant relationship between the nozzle size and torch performance, demonstrating the optimization potential for different industrial applications.