Vladimir Aubrecht

Net emission coefficient of radiation in SF6 arc plasmas

Calculations have been made of spectral absorptivities of SF6 plasmas as a function of wavelength from 10 nm to 30 mu m, temperature from 300 to 30000 K and pressure from 1 to 10 atm. Net emission coefficients of radiation have been derived from these absorptivities for cylindrical isothermal plasmas of radii from 0.1 to 2 cm. In addition calculations have been performed as a function of pressure, temperature and radius of the fraction of the emitted radiation that is below the photo-ionization threshold of 130 nm.

Characterization of a periodic instability in filamentary surface wave discharge at atmospheric pressure in argon

This study reports on a periodic instability in a microwave atmospheric pressure surface wave plasma. Time-resolved observation by means of a high-speed camera reveals that the discharge can operate in two different regimes. The discharge operates either in a static mode of a controlled number of filaments propagating alongside the wall of the fused silica tube or in a dynamic mode of one or more straight filaments together with one revolving filament. Microwave power and argon flow rate are interpreted as the scaling parameters that govern the self-organization in the discharge. The operating diagram is formed by alternating stripes of static and dynamic mode with well-defined borders.

Radiative emission from air thermal plasmas with vapour of Cu or W

This paper deals with the net emission coefficients of radiation of air thermal plasmas with admixtures of copper and tungsten as a function of the plasma temperature up to 25 000 K and the arc radius (0.01 to 10 cm) at various pressures. The net emission coefficients are calculated for various equilibrium compositions (mole fractions of Cu and W) of the plasma. Calculations take into account continuum and line radiations, and special attention has also been paid to the fraction of radiation that is below a threshold of 120 nm. From the results it follows that the presence of metallic vapour increases the net emission coefficients even at low temperatures below 10 000 K.

Integrated parametric study of a hybrid-stabilized argon?water arc under subsonic, transonic and supersonic plasma flow regimes

This paper presents a numerical investigation of characteristics and processes in the worldwide unique type of thermal plasma generator with combined stabilization of arc by argon flow and water vortex, the so-called hybrid-stabilized arc. The arc has been used for spraying of ceramic or metallic particles and for pyrolysis of biomass. The net emission coefficients as well as the partial characteristics methods for radiation losses from the argon?water arc are employed. Calculations for 300?600?A with 22.5?40 standard litres per minute (slm) of argon reveal transition from a transonic plasma flow for 400?A to a supersonic one for 600?A with a maximum Mach number of 1.6 near the exit nozzle of the plasma torch. A comparison with available experimental data near the exit nozzle shows very good agreement for the radial temperature profiles. Radial velocity profiles calculated 2?mm downstream of the nozzle exit show good agreement with the profiles determined from the combination of calculation and experiment (the so-called integrated approach). A recent evaluation of the Mach number from the experimental data for 500 and 600?A confirmed the existence of the supersonic flow regime.

Mean absorption coefficients of air plasmas

Mean absorption coefficients of air (both Planck and Rosseland mean) have been computed for different splitting procedures of the whole frequency interval (1013 – 6×1015 s−1) and various temperatures (1 000 – 30 000 K). Results have been compared and discussed to find the optimal values of mean absorption coefficients for the multigroup method of solution of the equation of radiation transfer.

Radiation absorption coefficients in arc plasmas

In the present paper, attention is given to the calculation of spectral coefficients of absorption and their comparisons with other sources of data for various types of the are plasmas. The coefficients of absorption have been calculated for various kinds of are plasmas (sulphur hexafluoride, hydrogen, oxygen) at different plasma temperatures and pressures above 1 bar. Photon absorption cross sections have been calculated using an approximation method of quantum defect. For the contributions from the line radiation, oscillator line strengths, widths and shifts of neutral and ionized atoms have been calculated using semi-empirical formulas. Curves are given for the absorption coefficients of radiation for wavelengths of 10 to 3000 nm.

Radiation transfer in air and air-Cu plasmas for two temperature profiles

In this article we present our results from calculations of the divergence of the radiation flux in a high temperature air-Cu plasma arc. We assumed stationary plasma, with local thermodynamic equilibrium valid throughout the plasma volume. We paid attention especially to the presence of copper lines in the absorption coefficient spectra and their influence on the energy transfer. Two distinct temperature regimes were used, with one focusing on a steep temperature gradient and the other involving a slowly varying temperature profile. The temperature ranges from 25 kK at the arc center down to 3 kK at the plasma arc boundary. Uniform pressure of 1 bar was considered in all cases. The results show that a large amount of energy is emitted by the copper vapor, which helps with cooling the arc.

On the Selection of Integration Intervals for the Calculation of Mean Absorption Coefficients

In radiation modeling of thermal plasmas non-grey models are applied where the radiative transport is described in several frequency bands (spectral intervals). Hereby mean absorption coefficients have to be calculated by a spectral integration procedure, providing a constant mean absorption coefficient for each band. Depending on the number of bands, one or more integration boundaries have to be selected in order to do the integration. In this paper we evaluate the influence of the selection of these integration boundaries on the mean absorption coefficient and the also radiation transfer by applying the mean absorption coefficients in a radiation transport model. Using a simplified two-band model we demonstrate that the selection of the integration boundary has a large impact on the total model accuracy. We show that in some cases selecting a band boundary right at the frequency where the continuum absorption shows a jump can introduce a significant error into the radiation calculation. The process of the integration interval selection thus demands a global optimization procedure to properly evaluate the boundaries of each frequency band.

Calculation of radiative heat transfer in argon arc plasmas

Radiation emission and absorption in arc plasmas are important energy transfer processes. Exact calculations, though possible in principle, are usually impossible in practice because of the need to treat a large number of spectral lines and also the continuum radiation in the whole spectrum range. Recently, we have used an approximate method of partial characteristics to evaluate the radiation intensities, radiation fluxes and the divergence of radiation fluxes for SF6 arc plasma with cylindrical symmetry. In this paper, we have extended our calculations toargon arc plasmas for the plasma pressures of 0.1, 0.5 and 1.0 MPa. We have calculated the coefficients of absorption for Ar plasmas at temperatures from 300 to 35 000 K, and have used these coefficients to calculate the partial characteristics. Both the continuum and the line spectra have been included in calculations. We have taken into account the radiative photo-recombination and bremsstrahlung for the continuous spectrum, and over 500 spectral lines for the discrete spectra.The method of partial characteristics has been applied to three-dimensional calculations of radiative heat transfer — i.e. radiation intensity, radiation flux and its divergence — in simplified temperature profiles. Conclusions have been made concerning validity and utilization of the method of partial characteristics in general gas dynamics problems.

Quasi-Laminar Flow Characteristics in Hybrid-Stabilized Argon–Water Arc Discharge for Subsonic-Supersonic Regimes

This paper presents the numerical simulation of the turbulence effect in the nozzle region and upstream from a rotating disc anode in the hybrid-stabilized argon-water electric arc. Results of simulation for 300-600 A and argon mass flow rates of 22.5-40 sL/min based on a space averaging definition indicate quasi-laminar flow.