Abstract
In this paper a dimensionless parameter is defined which allows the prediction of the thermodynamic state in the field-free plasma jet of D. C. operated plasma torches of various designs. This dimensionless parameterP is derived from the conservation equations applied to a two-step temperature and velocity model and contains only quantities which can be experimentally determined without using sophisticated equipment. Critical values ofP based on a critical electron density of 1016 cm−3 have been calculated for argon, hydrogen, nitrogen, oxygen, and helium and corresponding values of Pcrit have been determined experimentally for two different D. C. operated argon plasma torches using various diagnostic techniques. The experimental values corroborate the assumptions made for the calculation of Pcrit. ForP < Pcrit, substantial deviations from the local thermodynamic equilibrium (LTE) may occur.
Zusammenfassung
Zur thermodynamischen Beschreibung des Plasmazustandes im feldfreien Strahl verschiedener Gleichstrom Plasmabrenner wird ein dimensionsloser Parameter eingeführt, der aus den Erhaltungsgleichungen, angewandt auf ein Zweistufenmodell, gewonnen wird. Dieser ParameterP, der für Argon, Wasserstoff, Stickstoff, Sauerstoff und Helium mit der Annahme einer kritischen Elektronendichte von 1016cm−3 berechnet wurde, enthält nur Größen, die sich mit geringem experimentellem Aufwand bestimmen lassen. Durch die Anwendung einer Reihe diagnostischer Verfahren auf zwei verschiedene Argon-Plasmabrenner erhält man entsprechende kritische Parameter, die die theoretischen Annahmen bestätigen. Im FalleP < Pcrit sind wesentliche Abweichungen vom lokalen thermodynamischen Gleichgewicht (LTE) zu erwarten.
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Abbreviations
- B :
-
magnetic field strength
- E :
-
Electric field strength
- F L :
-
Lorentz force
- h :
-
enthalpy
- I :
-
total arc current
- j :
-
electric current density
- k :
-
thermal conductivity
- \(\dot m\) :
-
mass flow rate
- P :
-
critical parameter
- p :
-
pressure
- Q :
-
heat flux in the plasma jet
- Qel :
-
heat flux to the electrodes
- QR :
-
heat flux due to radiation
- r :
-
radial coordinate
- R :
-
radius of anode nozzle
- t :
-
time
- T :
-
temperature
- UR :
-
radiation heat flux per unit volume
- ν :
-
velocity
- \(\bar v\) ze :
-
velocity of the cold gas envelope inz direction, averaged over the length z1 z 0
- W :
-
electric power input to the arc
- z :
-
axial coordinate
- μ :
-
viscosity
- ϱ :
-
density
- σ :
-
electrical conductivity
- c:
-
hot core
- e:
-
cold gas envelope
- r:
-
radial direction
- z:
-
axial direction
- φ :
-
tangential direction
- 0:
-
location inz direction (see Pig. 2)
- 1:
-
location inz direction (see Pig. 2)
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This work was supported partially by the Aerospace Research Laboratories, USAF, under Contract F 33 615-67-C-1353.
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Boffa, C., Heberlein, J. & Pfender, E. Criterion for establishing deviations from the local thermodynamic equilibrium in atmospheric pressure plasma jets. Wärme- und Stoffübertragung 4, 213–221 (1971). https://doi.org/10.1007/BF01002476
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DOI: https://doi.org/10.1007/BF01002476