Local thermodynamic equilibrium analysis of the supersonic induction plasma jet

Abstract

Summary form only given, as follows. The inductively coupled radio frequency (RF) plasma has been the subject of numerous studies over the past three decades. One of its early applications was in the area of reentry simulation for the testing of materials under high temperature conditions. A number of other applications have evolved since in the area of material processing for either powder spheroidization and densification, plasma spray coating and deposition of near net shape parts, and the plasma chemical synthesis of ultrafine nanostructured materials. In the latter case, the deposition of these powders to form nanostructured coatings is not an easy task. One of the proposed approaches to do so is to use the induction plasma under supersonic flow conditions. This would allow the in situ synthesis of the powder and the acceleration of the nanoparticles in the Laval expansion nozzle of the plasma torch. For the purpose of characterizing the details of the flow and temperature fields in the plasma jet under these conditions, a systematic study was carried out using emission spectroscopy and enthalpy probe techniques. Detailed spectroscopic measurements are reported of the heavy particle temperature and electron density distributions in a supersonic induction plasma jet under different operating conditions. Results obtained for an Ar/H/sub 2/ plasma for a generator plate power of about 25 kW with a local Mach number in the range of 1 to 3, are compared with equilibrium enthalpy probe measurements of the specific enthalpy and plasma velocity profiles. The latter show centerline plasma temperatures at the exit of the plasma torch nozzle in the range of 3000 to 5000 K. Plasma velocities as high as 2000 to 3000 m/s were measured under these conditions.