Spectroscopic validation of the supersonic plasma jet model

Abstract

Optical emission spectroscopy is applied to validate numerical simulations of supersonic plasma flow generated by induction torch with a convergent-divergent nozzle. The plasmas exhausting from the discharge tube with the pressure 0.4-1.4 atm. through two nozzle configurations (the outlet Mach number equals 1.5 and 3) into low-pressure (1.8 kPa) chamber are compared. Both modelling and experiments show that the effect of the nozzle geometry on physical properties of plasma jet is significant. The profiles of electron number density obtained from modeling and spectroscopy agree well and show the deviations from local thermodynamic equilibrium. Analysis of intercoupling between different sorts of nonequilibrium processes is performed. The results reveal that the ion recombination is more essential in the nozzle with the higher outlet number than in the nozzle with the lower outlet number. It is demonstrated that in the jets the axial electron temperature is quite low (3000-8000 K). For spectroscopic data interpretation we propose a method based on the definition of two excitation temperatures. We suppose that in mildly under expanded argon jets with frozen ion recombination the electron temperature can be defined by the electronic transitions from level 5p (the energy E = 14.5 eV) to level 4p (E = 13.116 eV). The obtained results are useful for the optimization of plasma reactors for plasma chemistry and plasma processing applications.

How Hydrogen Admixture Changes Plasma Jet Characteristics in Spray Processes at Low Pressure

“…• Typical off-axis maxima in the radial profiles of expansion cells corresponding to barrel shock waves which are more pronounced for low hydrogen contents and pure Ar [31], see also Fig. 10; • Higher reactional thermal conductivity in radial direction in the presence of hydrogen due to recombination.…”

“…The deviations from LTE are higher in the expansion than in the compression cells and very pronounced at the jet rims. Moreover, in coaction with very small characteristic flow times, kinetic non-equilibrium between electrons and heavy particles (atoms, ions) occurs [31] as the energy transfer between them is no longer sufficient to balance energy evenly. This leads to the two-temperature (2T) model [32] with the kinetic electron temperature T e , the kinetic temperature of the heavy particles T h , and the non-equilibrium parameter Θ = T e /T h .…”

Plasma Spray-PVD: Plasma Characteristics and Impact on Coating Properties

“…This is supposed to be the explanation for the lower temperature level. recombining hydrogen atoms is released and transferred [30]. At 1000 Pa, this happens closer to the nozzle so that it was not covered by the measurements.…”

“…Here, the electron densities are larger as the density in the jet is higher in general. The initial increase of the electron densities is assumed to be associated to static pressure and temperature alterations along the jet axis due to equilibration with the ambient pressure [30]. As recombination is already advanced at the applied measurement positions, the ionization rates are on low level.…”

Simulation of Subsonic and Supersonic Flows in Inductive Plasmatrons

“…In general, the problem is rather tricky. Up to now there are few computations of the nonequilibrium air 5 and argon 6 plasma flows coupled with the rf electromagnetic field. In prior papers 4,7 the entire flowfield into plasmatron has been calculated separately in two, 7 three, 4 or several 8 computational zones.…”