Milada Bartlova

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.

Comparison of some models of reaction kinetics in HV circuit breakers with SF6 after current zero

In this paper, the solutions of three models of reaction kinetics in HV circuit breakers with SF6 after current zero are presented and compared. One model has been proposed by Bartlova, the co-author of this paper, the other two models under comparison have been taken over from the literature. In all the three models a constant pressure p(t) = 4 atm and the same dependence of temperature on time T(t) are assumed. For the description of the relation between equilibrium and kinetic composition in a system, the concept of asymptotic composition is introduced. A comparison of the composition and enthalpy of the products of SF6 dissociation and ionization for the given pressure and T(t) is made. General conclusions have been derived from the comparison.

Calculation of radiative heat transfer in SF/sub 6/ arc plasmas

Radiation transport in SF/sub 6/ are plasmas have been treated for pressures of 0.101, 0.5, and 1.0 MPa. We have investigated the use of an approximate method of partial characteristics. We have calculated spectral absorptivities for SF/sub 6/ plasmas for temperatures from 300 to 35 000 K, and have used these absorptivities to calculate the two functions designated /spl Delta/I and /spl Delta/Sim. These functions are integrals over all radiation frequencies for given line segments with a linear variation of temperature along the line. The /spl Delta/I and /spl Delta/Sim values are functions of the end temperatures and the length of the line, and are used to evaluate radiation transfer from line segments in the plasma where the temperature variation for each line segment is approximated as being linear. The validity of this method of partial characteristics has been demonstrated by comparing exact calculations with the approximate calculations to evaluate radiation intensities, radiation fluxes, and divergence of radiation fluxes for specified temperature profiles. The method of partial characteristics has been applied to one- and three-dimensional calculations of radiative heat transfer in simplified temperature profiles. Agreement up to 10% is obtained with exact calculations, but with a large reduction of computation time.

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.

Turbojet engine innovation and TRIZ

Comparing to concurrent small turbojet engines this Czech design has several important parametrical advantages: weight, power, reliability, cost, etc. Innovations were obtained by creative/inventive solutions in which several instruments TRIZ were used objectively. In this article, the turbojet engine is presented as a case study: As an example for teaching the TRIZ methodology to students and engineers and as a solution of turbojet engine for small and unmanned air vehicles.

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.