Oldřich Coufal

Database system of thermodynamic properties of individual substances at high temperatures

Theoretical starting points and methods leading to the creation of a consistent database of thermodynamic properties of individual substances are given. The database is easy to modify and update. An exact definition of the concept consistent is given after all the relations and connections have been given. The proposed general methods are realized using computer programs and the species file, in which the thermodynamic properties of 326 gaseous and 34 condensed substances are stored that were prepared from a set of elements . Together with other files and programs the species file forms the database system TheCoufal, which is described in detail below, and stored as from the date of publication of this paper at the address http://www.feec.vutbr.cz/~coufal/.

Composition and thermodynamic properties of thermal plasma up to 50 kK

The initial relations and the description of a method for calculating the composition and thermodynamic properties of a closed gaseous system in thermodynamic equilibrium at constant pressure and temperature are given. The essence of the method consists in the minimization of the Gibbs energy of a system in ideal state. The calculation algorithm is implemented by the Tmdgas program in the C++ language. This program is part of the database system TheCoufal, available to interested parties at http://www.feec.vutbr.cz/~coufal/. The method described was used to calculate the thermodynamic properties of a system of products of the dissociation and ionization of H2O. The results have been tabulated for pressures of 1, 5 and 20 bar at temperatures ranging from ambient temperature to 50 kK.

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.

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.

Current density in a long solitary tubular conductor

Two models are described whose solution is the current density in a tubular conductor that is given by the radii ri < ro and supplied from an ideal current source of a frequency that does not exceed 1 GHz. It has been proven that the two models are equivalent, but model 1 can practically be used only to calculate current density in a cylindrical conductor (ri = 0). The general methods proposed are applied to several concrete examples of tubular and cylindrical conductors. The solution of examples is given in the figures. In the solution of examples, attention is devoted to problems that are connected with the realization of numerical calculation on a computer.

On the formal correctness of the reaction kinetics model and its solution in HV circuit breakers after current zero

Five necessary conditions for the so-called formal correctness of solutions of kinetic equations are formulated, which form a mathematical model of the reaction kinetics in HV circuit breakers after current zero for a given time-dependence of temperature and a given time-dependence of pressure or volume. The conditions are based on the mass action law, knowledge obtained from mathematical analysis of a system of ordinary differential equations, the principles of numerical analysis and the equilibrium-state principle of thermodynamics. Concrete solutions of kinetic equations are given and analysed for the products of SF6 dissociation and ionization. Two models are considered. In one model, the temperature drops from 10 000 to 2500 K, in the other it drops from 12 000 K to room temperature. A comparison of the time-dependent composition with the equilibrium composition is offered for both models.

On kinetics of reactions in HV circuit breakers after current zero

An analysis of six different definitions of the rate of reaction is made and it is shown that some of the definitions are not consistent with the mass action law. Kinetic equations are derived whose solution is the time dependence of the composition of an arbitrary closed gaseous system in an ideal state for a given time dependence of temperature on the assumption that either the time dependence of pressure in or the time dependence of the volume of is given. Results are given of the computation of composition of a system of SF6 dissociation and ionization products at a temperature drop from 12 000 K to room temperature and a comparison is made of the time-dependent composition with equilibrium composition for pressures of 0.1, 0.5, 1 and 2 MPa.

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 Resistance and Inductance of Solid Conductors

The concepts of resistance and inductance are strewn with misunderstanding and errors that result from inaccurate terminology, mistakes in their definitions, and from the fact that they are quantities that characterize elements of ideal electrical circuits as well as real solid conductors. This is shown unfavourably not only in the respective field of the theory of electrical engineering, but also in the calculation of resistance and inductance. In this paper, a brief theoretical analysis of the state of the art is given, and its results are applied in the calculation of the current density, resistance, and inductance of two coaxial solid tubular conductors.

Comments on the computation of the composition of quenching media in HV circuit breakers after current zero

General equations are derived whose solution gives the dependence of species concentrations of a closed gaseous system on time for a given dependence of temperature on time, on the assumption that either the dependence of pressure in on time or the dependence of volume of system on time is given. Some results from solving a previously proposed model are given for the case when is created by the products of dissociation and ionization and the temperature decreases exponentially from 10 000 K to 2500 K. Special attention is devoted to the relation between time-dependent composition and equilibrium composition.