On the interplay of gas dynamics and the electromagnetic field in an atmospheric Ar/H₂microwave plasma torch

Abstract

A complementary simulation and experimental study of an atmospheric pressure microwave torch operating in pure argon or argon/hydrogen mixtures is presented. The modelling part describes a numerical model coupling the gas dynamics and mixing to the electromagnetic field simulations. Since the numerical model is not fully self-consistent and requires the electron density as an input, quite extensive spatially resolved Stark broadening measurements were performed for various gas compositions and input powers. In addition, the experimental part includes Rayleigh scattering measurements, which are used for the validation of the model. The paper comments on the changes in the gas temperature and hydrogen dissociation with the gas composition and input power, showing in particular that the dependence on the gas composition is relatively strong and non-monotonic. In addition, the work provides interesting insight into the plasma sustainment mechanism by showing that the power absorption profile in the plasma has two distinct maxima: one at the nozzle tip and one further upstream.

Effect of Additive Oxygen on the Reactive Species Profile and Microbicidal Property of a Helium Atmospheric Pressure Plasma Jet

“…As mentioned above, the first part of the model describes the gas flow and mixing of the non‐uniform He/air mixture. The model is based on the argon/air gas dynamics model which solves the Navier–Stokes equations self‐consistently with diffusion equations and has been described and validated in ref . Because the maximum Reynolds number at relevant experimental conditions does not exceed 200, even at the highest operating flow rates, the gas flow is considered laminar.…”

Numerical investigation of energy transfer efficiency from microwave radiation to plasma in a cylindrical resonant cavity

“…where qe and me denote the charge and mass of an electron, ne is the volume concentration of electrons. For the collision frequency e, the following approximate expression was used [4]:…”

“…This expression was obtained in [4] from the solution of the Boltzmann equations for a mixture of hydrogen and argon, taking into account the main collision cross-sections. Here nAr, nH2 nH are the number densities of argon, molecular and atomic hydrogen, respectively.…”

“…Here nAr, nH2 nH are the number densities of argon, molecular and atomic hydrogen, respectively. The coefficients kAr=1.8·10 -14 m 3 /s, kH2=1.1·10 -13 m 3 /s, kH=1.5·10 13 m 3 /s were taken from [4] where they were calculated for an electron temperature of 1.3 eV. This temperature was set as effective in the current calculations.…”

“…According to estimates for a hydrogen microwave plasma, the effective electron temperature was chosen equal to 1.3 eV. [4] The main function of the model is to convert the energy flux from microwave radiation through the distribution of electrons (conduction mechanism) into heat release in the gas. The amount of energy absorbed by electrons from the microwave field in the resonator of the experimental setup [3] was calculated for the supplied power in the range from 1 to 3 kW and hydrogen pressures ranged from 25 to 600 Torr.…”