Thermodynamic properties and transport coefficients in metal seeded arc plasmas

Porytskyy P.V.
Institute for Nuclear Research of NASU, pr.Nauky 47, Kyiv 03680, Ukraine ; e-mail: poryts@kinr.kiev.ua
Abstract.
It is considered the two-temperature model of a thermal plasma applied to study the arc discharge plasma at atmospheric
pressure. It is studied the influence of peculiarities of the thermal properties of separated components of gaseous mixtures and
the characteristics of electron-atom collisions on the thermodynamic properties and transport coefficients in an arc plasma
in gaseous mixtures. The calculations are carried out for the case of a metal seeded arc plasma in nitrogen or noble gas
ambient atmosphere. It is shown that the influence of the metal vapour presence on thermodynamic properties and transport
coefficients can be important in arc plasmas at low-current regime of the discharge. Also, it is studied the influence the
Ramsauer-Townsend effect, which is a feature of some noble gases, on the properties of an arc plasma in that gaseous medium.
It is shown the possibility to neutralize that influence on the plasma properties for an arc in multispecies gaseous mixtures.
Keywords: thermal plasma, temperature, the Ramsauer-Townsend effect, conductivity, electron-atom collisions
PACS: 52.25Vy; 52.25Fi; 52.25Kn; 52.80Mg
INTRODUCTION
Arc discharges in metal vapours sustained atmospheric pressure conditions are attracting interest from various industrial
technical fields.
The plasma composition, thermodynamic properties and transport coefficients have been calculated for a plasma
assumed to be in local thermodynamic equilibrium (LTE) in a number of papers [1, 2, 3, 4]. In these papers calculation
are carried out with using the one-temperature model for a plasma or the two-temperature model having the constant
temperature convergence parameter q = Te=T, where Te is the electron temperature and T is the heavy particle
temperature (gaseous temperature).
On the other hand, because of the peculiarities of volt-ampere characteristics an arc plasma is frequently in the
state determined by the approximately constant electric field strength E [5, 6, 7, 8]. In this paper it is namely studied
the properties of metal seeded arc plasmas under that condition. There are the following metal impurities including
into consideration: copper, cadmium, zinc, molybdenum and mercury that are in the ambient gas atmosphere of argon
or nitrogen. The calculation is made assuming the local thermodynamic equilibrium when ionization equilibrium is
established relatively to the electron temperature Te.
TWO-TEMPERATURE THERMAL PLASMA
Consider a two-temperature model of a plasma in the case where a state is described by both the certain gaseous
temperature T and the electron one Te which correspond to the Maxwellian distribution functions of heavy particles
and electrons over velocities, and let the ionization equilibrium hold relative to Te. In that model the relation between
temperatures takes the form [6, 7, 8]

where g(Te) is the certain function of electron temperature, N is the number density of heavy particles.
The discrepancy between these temperatures may be very different for the certain plasma composition (see Figs.1,2).
Thus, this difference may be large due to the influence the Ramsauer-Townsend effect, for example, in the case of an
argon plasma.
The calculations were carried out here and below under the conditions of the constant electric field strength
E = 10V=cm for the equimolar composition of mixtures at atmospheric pressure. Also, it should be pointed that FIGURE 4. Thermal conductivities in [90]N2-[10]Cu mixture. (1) total conductivity kV , (2)gaseous conductivity, (3)electron
conductivity, (4) reactive ionization conductivity, (5)reactive dissociative conductivity, (6) ion conductivity. For copper it is used a
resonant model for cross-section.
be mentioned that to characterize the total thermal conductivity it is introduced the value
kV = k (T)+

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