Experiments on turbulent mixing in a partially ionized gas

Grey, Jerry; Jacobs, Paul F.

doi:10.2514/3.2348

Cited by 36 publications

(10 citation statements)

References 3 publications

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“…Taking the foregoing expression for random current ratio, therefore, considering T eX » T em as was demonstrated previously, and taking TI\ = T A \ ~ T w for the dense, cooled boundary layer, we find m e T w (3) Furthermore, for the assumed conditions, it has been established that the electric field effects are restricted to the neighborhood of the probe (specifically, within one electron-ion mean free path) and are therefore "insulated" from the random current produced by diffusion in the boundary layer. Thus, the classical Langmuir expression for electron current is valid (at least in the regime between zero electron current and the plasma potential or for slightly negative probe potentials) : (4) The ion current in this region will be close to the random (saturation) value ji (5) and the floating potential <p F , at which j e = j I} is thus given bv (6) 2e…”

Section: Discussionmentioning

confidence: 98%

Cooled electrostatic probe.

Grey

Jacobs

1967

AIAA Journal

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Experiments were performed to evaluate the ability of a water-cooled electrostatic probe to measure local electron temperature, electron density, floating potential, and saturation current ratio in dense plasmas (argon up to 20,000°R at 1 atm). The measurements of electron temperature were calibrated against temperatures obtained from simultaneous local measurements of total plasma enthalpy at different temperatures under conditions of known equilibrium by use of a proven calorimetric probe technique and were found to be in agreement within normal experimental error (3% standard deviation from the mean). Using this electron temperature, the measurements of floating potential and saturation current ratio were found to agree with a first-order theoretical approximation to within the accuracy of the approximation. The cooled calorimetric-electrostatic probe was then used to measure the degree of nonequilibrium in a reduced-pressure argon plasma in terms of the difference between local electron and heavy-particle temperatures. Results were in agreement with analytical predictions of a simple "freezing" criterion. The probe also provided a semiquantitative measurement of plasma turbulence. Nomenclature C = most probable particle speed, cm/sec d = Bohm transition region thickness, cm E -electron kinetic energy, ergs E n -electron kinetic energy after n collisions, ergs &E = change in electron kinetic energy, ergs e -electronic charge, esu (also base of natural logarithms) h = Debye length, cm 7 = current density, amp/cm 2 k = Boltzmann constant L = probe diameter, cm m = particle mass, g n = number of collisions in boundary layer N = number density per cm 3 p = pressure, atm Re = Reynolds number T = temperature, °R or °K U = mean flow velocity, cm/sec V = applied potential, v x = axial distance from arcjet nozzle, cm or in. y = distance from probe surface, cm a. = degree of ionization, N € /(NA + N e ) 8 = boundary-layer thickness, cm X = mean free path, cm /z = mobility

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Section: Discussionmentioning

confidence: 98%

Cooled electrostatic probe.

Grey

Jacobs

1967

AIAA Journal

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“…For the plasma jet diagnostics, an enthalpy probe has been used as a diagnostic tool in this work, because it is the most suitable device for the measurements of air thermal plasma, which has relatively low temperature, strong turbulence flow, and complex emission spectral lines. [31][32][33][34][35] The radial profiles of temperature and axial velocity were measured at z = 60 and 80 mm from the torch exit with an interval of 2 mm from r = 0 to 20 mm. Since the probe tip could not sustain heat fluxes higher than 10 8 W / m 2 , the measurements on the axial profiles of plasma fields were made starting from an axial position of z = 60 mm.…”

Section: Validation Of 2d and 3d Numerical Modelsmentioning

confidence: 99%

Comparative study of two- and three-dimensional modeling on arc discharge phenomena inside a thermal plasma torch with hollow electrodes

Park

Choi

et al. 2008

Physics of Plasmas

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A comparative study between two-and three-dimensional ͑2D and 3D͒ modeling is carried out on arc discharge phenomena inside a thermal plasma torch with hollow electrodes, in order to evaluate the effects of arc root configuration characterized by either 2D annular or 3D highly localized attachment on the electrode surface. For this purpose, a more precise 3D transient model has been developed by taking account of 3D arc current distribution and arc root rotation. The 3D simulation results apparently reveal that the 3D arc root attachment brings about the inherent 3D and turbulence nature of plasma fields inside the torch. It is also found that the constricted arc column near the vortex chamber plays an important role in heating and acceleration of injected arc gases by concentrating arc currents on the axis of the hollow electrodes. The inherent 3D nature of arc discharge is well preserved inside the cathode region, while these 3D features slowly diminish behind the vortex chamber where the turbulent flow begins to be developed in the anode region. Based on the present simulation results, it is noted that the mixing effects of the strong turbulent flow on the heat and mass transfer are mainly responsible for the gradual relaxation of the 3D structures of plasma fields into the 2D axisymmetric ones that eventually appear in the anode region near the torch exit. From a detailed comparison of the 3D results with the 2D ones, the arc root configuration seems to have a significant effect on the heat transfer to the electrode surfaces interacting with the turbulent plasma flow. That is, in the 2D simulation based on an axisymmetric stationary model, the turbulence phenomena are fairly underestimated and the amount of heat transferred to the cold anode wall is calculated to be smaller than that obtained in the 3D simulation. For the validation of the numerical simulations, calculated plasma temperatures and axial velocities are compared with experimentally measured ones, and the 3D simulation turns out to be more accurate than the 2D simulation as a result of a relatively precise description of the turbulent phenomena inside the torch using a more realistic model of arc root attachment. Finally, it is suggested that the 3D transient formulation is indeed required for describing the real arc discharge phenomena inside the torch, while the 2D stationary approach is sometimes useful for getting practical information about the time-averaged plasma characteristics outside the torch because of its simplicity and rapidness in computation.

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“…0 noch etwas genauer. Sie ist typisch fur einen stromlosen Plasmastrahl, der aus der Duse in ein ruhendes oder schwach bewegtes Medium eintritt und dort abgebremst wird [32]). Bei nicht zu grol3em Abstand z von der Plasrnastrahlaustrittsoffnung mit dem Durchmesser D ((z/D 4 1,3, wie hier der Fall) gibt es in der Mitte (Potentialzone) einen flachen w (7)-Verlauf ( [ 3 2 ] NpI betragt hiermit 55% der Bogenleistung von 9,75 bW.…”

Section: Bestimmung Der Radialen Temperaturverteilungunclassified

Wärmestrommessungen an einem Langbogen‐Plasmastrahl

Dreusicke¹,

Neumann²

1966

Contrib Plasma Phys

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Es w i d die yon cinem relativ breiten und langsamen bogenerzeugten Argon-Plasmastrahl (Durchmesser der dustrittsoffnung W = 2,s cm, Strahlgeschwindigkeit v w lo4 cms-I) an eine senkrecht angestromte kalte Platte ubertragene Wirmestromdichte p (r) gemevsen und mit der ungestijrten Enthalpiestromdichte des Plasmastrahls f ( r ) verglichen. Diese wird uber das radiale Temperatur-und Geschwindigkeitsprofil des Plasmastrahls bestimmt. Dabei zeigt sich eine starke Verbreiterung des p (r)-Profils gegeniiber dem f (r)-Profil bei gleichzeitiger Naximaverminderung (von 3,s kW/cm2 auf 90 W/cm'), ziisammenhingend rnit der Bildung eines Plasmatellers vor der nngestromten Scheibe. Die insgesemt ubertragene Warmeleistung betrigt rnit 1,7 kW nur 320,; der gesamten Plasmastrahlleistung von 5,4 kW oder 17% der gesamten Bogenleistung von 9,75 kW.Neben dieeen im Hinblick auf die Anwendung des Plasmastrahls zum Mnterialschmelzm rvichtigen Untemuchungen werden Beobachtungen iiber die Struktur des Plasmastrakln und der Bogenskde mitgeteilt. Die BogensLule zeigt bei nicht zu engem Kana1 eino Wendelung, dorm Ursachen WITKOWSKI untenucht hat. Diese Wendelung bewirkt eine Bogenrotation und eine Spiralform &s PlasmastrakLs. Eine Hell-Dunkelstruktur des Plasmastrahls, die rnit der Beivegung des Anodenansatzee zusarnmenhangt, wird auch bei urn beobachtet.

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Experiments on turbulent mixing in a partially ionized gas

Cited by 36 publications

References 3 publications

Cooled electrostatic probe.

Cooled electrostatic probe.

Comparative study of two- and three-dimensional modeling on arc discharge phenomena inside a thermal plasma torch with hollow electrodes

Wärmestrommessungen an einem Langbogen‐Plasmastrahl

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