Thermal conductivity in an argon arc at atmospheric pressure

Thermal conductivity in an argon arc at atmospheric pressure

Citation for published version (APA):

Bol, L., Timmermans, C. J., & Schram, D. C. (1984). Thermal conductivity in an argon arc at atmospheric pressure. In ESCAMPIG 84 :7th European Sectional Conference on the Atomic and Molecular Physics of Ionized Gases : August 28-31, 1984, Bari, Italy (pp. 141-142). (Europhysics conference abstracts; Vol. 8E). European Physical Society (EPS).

Document status and date: Published: 01/01/1984

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6-2

THERMAL CONDUCTIVITY IN AN ARGON ARC АТ ATMOSPHERIC PRESSURE L. Bol, C,J, Timmermans, D.C. sc·hram.

Dept. of Physics, Eindhoven University of Technology, The Netherlands Introduction

The thermal conductivity of an argon plasma has been determined in а ф5mm

wall stabilized atmospheric argon arc in the temperature range from 10000 to 16000 К. The ca1~ulations are Ьased on the еnе~чу balance, and include n6n-LTE effec:ts _like amЫpolar diffusion and overpopulation of the ground level. Other authors generally ignored the contributfon of diffuiion, ~ut it

сап Ье shown (1,21 that diffusion p1ays а significant role in the energy transport within the cascade arc.

Theory

An argon plasma, under the mentioned conditions, can Ье considered to Ье in parti al 1 ocal about 15000 К becomes very dissipation is (U с and U J ) viz.

thermodynamic equilibrium (PLTEI and at the temperature of the deviation· from local thermodynamic equilibrium <LTE) small. In the energy balance, the energy input Ьу electric:al

Ьalanced Ьу thermal conduc:tion, continuumand line r~diation and Ьу а net ion flow, governed Ьу the aebipolar diH.usion (2)

{1} where cr is the elec:tric:al c:onduc:tivity, Е is the elec:tric field strength, Ае

is the thermal · c:onductivity, Те is the electron temperature, ne is the elec:tron density, w е i\i the radfal .electron velocity and Е+1 is the iohization energy. This energy balance is used to determine the heat loss Ьу c:onduc:tion, and hence to calc:ulate the thermal conduc:tivity •

ТаЫе 1, Typical values for the terms on the arc's axis in eq,{1}, The heat loss Ьу conduc:tion has been calculated using eq,{1}

I Те crE2

_Uc

1+%kTe} -v:.(~eVTe) А к

GW/m

_GW/m

_GW/m

_GW/m

_GW/m

1

-Results

Based on the energy balance {1} and the experimental data 1Te,ne1E} obtained

Ьу R()sado (4) the thermal conductivity ле has been calculatedlsee fig 1).

10 ,,,.. ..---, :,.:: е

j

Fig.1. Thermal conductivity of Devoto, ///////: experi mental data Spitzer,and ~ this work

40-200 А.

argon at 1 a t m - - : thearetical data Ьу

ci ted Ьу Devoto, - - - : theoretical data Ьу

for different гadii in the current range of

In fig.1. there exists good agreement between our resu1ts for I= 40,60,ВО А

and the theoretical data Ьу Devoto 13}. Note that other authors overestimated

ле Ьу а factor 2, possiЫy due to neglecting the role of diffusion. Fог I= 140,200 А our data yield а thermal conductivitYлe that is much larger than the theoretical data. РrоЬаЫу this is caused Ьу an underestimation of the free-bound radiation in our i:alculations (cf. Timmerma.ns'84 (6)).

References

1. С.Н. Kruger, Phys. Fluids,!_l, 1737 (1970}

2. А. Gleizes et.al., J. Phys.D.,1,'5, 1031 (1982)

3. R,S. Devoto, Phys. Fluids, 10, 354 (1967>

4, R.J. Rosado, thesis, Eindhoven Univ. of Technology, The Netherlands (1981) 5. L. Spitzer, R. Haerm, Phys. Rev., 89, 977 (1953)

6. C.J. Тimmermans et.al., ~.Naturforsch,.(1984), to Ье puЫished