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  • 1
    Digitale Medien
    Digitale Medien
    Modeling of RF plasma torch with a metallic tube inserted for reactant injection (1991)
    Springer
    Plasma chemistry and plasma processing 11 (1991), S. 103-128 
    Details
    ISSN: 1572-8986
    Schlagwort(e): RF plasma torch ; injection probe ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Flow, temperature, and electromagnetic (EM) fields in a radio-frequency thermal plasma torch designed for the preparation of superconducting powders or films have been analysed by using a new two-dimensional modeling approach with the electric field intensity as the fundamental EM field variable. The insertion of a stainless steel injection tube into the torch leads to large induction currents in this tube. Although such large induction currents cause pronounced changes of the EM fields near the injection tube, flow and temperature fields are little affected. There exists only one large toroidal vortex in the upper part of the present torch, while the maximum temperature appears at an off-axis location within the coil region.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01447036
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  • 2
    Digitale Medien
    Digitale Medien
    An experimental study of the drag force on a sphere exposed to an argon thermal plasma flow (1991)
    Springer
    Plasma chemistry and plasma processing 11 (1991), S. 151-168 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Drag force on a sphere ; thermal plasma flow ; experiments
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Experimental data are presented concerning the drag force on a stationary phere exposed to an argon plasma flow with temperatures about 104 K and velocities about 102 m/s. A novel probe construction has been employed in the drag measurements in order to exclude the effect of the supporting wire on the sphere drag data. By using the new probe construction with a compensating wire, drag forces on an individual steel sphere in the plasma flow have been measured and compared with those obtained by using the probe construction ernployed by a few previous authors. Experimental results show that the measured drag forces are always less than their counterparts obtained from the standard sphere-drag curve under isothermal flow conditions with the same Reynolds numbers based on the oncoming plasma properties. The drag force on a sphere increases only slightly with the increasing surface temperature of the sphere before it melts. Appreciable diference was found between the experimental data and the predicted results of the available expressions for drag on a sphere exposed to a thermal plasma flow. Further research effort is required to build a more suitable drag correlation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01447038
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  • 3
    Digitale Medien
    Digitale Medien
    Modeling of a counterflow plasma reactor (1991)
    Springer
    Plasma chemistry and plasma processing 11 (1991), S. 229-249 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Thermal plasma reactor ; counterflow ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Modeling of a counterflow plasma reactor is presented, using liquid injection for the synthesis of fine particles. An experimental reactor has been developed in this laboratory, and feasibility has been demonstrated for synthesizing advanced ceramic powders. The flow field calculations show two major recirculating regions which are of importance for increasing the particles' residence time inside of the reactor. In addition, the temperature within these recirculation zones remains relatively uniform. For simulation, water droplet trajectories have been calculated for droplets produced by an injection probe. It is shown that the droplets in a size range below 50 μm in diameter will follow the streamlines and evaporate completely within a short traveling distance. This finding suggests that this reactor configuration provides a favorable environment for the synthesis of fine particles using liquid precursors.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01447244
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  • 4
    Digitale Medien
    Digitale Medien
    Thermophoretic force on a metallic or nonmetallic particle immersed into a rarefied Plasma (1992)
    Springer
    Plasma chemistry and plasma processing 12 (1992), S. 345-370 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Thermophoresis ; free-molecule regime ; analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Analytical results of the thermophoretic force on a metallic or nonmetallic spherical particle immersed into a rarefied plasma with a heat flux within the plasma are presented for the extreme case of free-molecule regime and thin plasma sheath. It has been shown that the thermophoresis is predominantly caused by atoms at low plasma temperatures with negligible gas ionization, while it is mainly due to ions and electrons at high plasma temperatures with great degree of ionization. The ion flux incident to a particle is constant on the whole sphere surface, while the electron flux to the metallic sphere is dependent on the θ-position with slightly greater value at the fore stagnation point. Consequently, there is a small difference between the metallic and nonmetallic spheres in their θ-distributions of the floating potential on the surface, which causes the thermophoretic force on a nonmetallic sphere to be appreciably greater than that on a metallic sphere at high plasma temperatures. Expressions for the total thermophoretic force on a metallic sphere and its components due to, respectively, atoms, ions, and electrons have been given in a closed form. Calculated results are also presented on the effects of pressure and of electron/heavy-particle temperature ratio. These results can be understood based on the variation of atom, ion, and electron thermal conductivities with the gas pressure, the temperature, and the temperature ratio.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01447030
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  • 5
    Digitale Medien
    Digitale Medien
    Drag on a metallic or nonmetallic particle exposed to a rarefied plasma flow (1989)
    Springer
    Plasma chemistry and plasma processing 9 (1989), S. 387-408 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Particle drag force ; free-molecule flow regime ; pressure effect ; two-temperature plasma ; analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Drag force on a metallic or nonmetallic spherical particle exposed to a plasma flow is studied for the extreme case of a free-molecule regime. Analytical expressions are derived for the drag components due to, respectively, atoms, ions, and electrons and for the total drag on the whole sphere due to all the gas species. It has been shown that the drag is proportional to the square of the particle radius or the drag coefficient is independent of the particle radius. At low gas temperatures with a negligible degree of ionization, the drag is caused mainly by atoms and could be predicted by using the well-known drag expression given in ordinary-temperature rarefied gas dynamics. On the other hand, the drag is caused mainly by ions at high plasma temperatures with a great degree of ionization. The contribution of electrons to the total drag is always negligible. Ignoring gas ionization at high plasma temperatures would overestimate the particle drag. There is a little difference between metallic and nonmetallic spheres in their total drag forces, with a slightly higher value for a metallic sphere at high plasma temperatures, but usually such a small difference could be neglected in engineering calculations. The drag increases rapidly with increasing gas pressure or oncoming speed ratio. For a two-temperature plasma, the drag increases at low electron temperatures but decreases at high electron temperatures with the increase in the electron/heavy-particle temperature ratio.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01083674
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  • 6
    Digitale Medien
    Digitale Medien
    Heat transfer to a particle under plasma conditions with vapor contamination from the particle (1985)
    Springer
    Plasma chemistry and plasma processing 5 (1985), S. 119-141 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Heat and mass transfer ; thermal plasma ; vapor contamination effect ; analytical studies
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Heat transfer to a copper particle immersed into an argon plasma is considered in this paper, including the effects of contamination of the plasma (transport coefficients) by copper vapor from the particle. Except for cases of high plasma temperatures, the vapor content in the plasma is shown to have a considerable influence on heat transfer to a nonevaporating particle, and, to a lesser extent, on heat transfer to an evaporating particle. Evaporation itself reduces heat transfer to a particle substantially as shown in a previous paper [Xi Chen and E. Pfender, Plasma Chem. Plasma Process.,2, 185 (1982)]. Comparisons of the calculated results with those based on a method suggested in the above reference show that the simplified assumptions employed, i.e., that the surface temperature is equal to the boiling point and that plasma properties based on a fixed composition are applicable, can be employed to simplify calculations for many cases. This study reveals that a considerable portion of a particle must be vaporized before a steady concentration distribution is established around the particle.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00566210
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  • 7
    Digitale Medien
    Digitale Medien
    Thermophoretic force acting on an evaporating particle suspended in a rarefied plasma (1994)
    Springer
    Plasma chemistry and plasma processing 14 (1994), S. 163-192 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Thermophoresis ; evaporating particle ; free-molecule regime ; analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Analytical results of the thermophoretic force on an evaporating spherical particle immersed in a rarefied plasma with a large temperature gradient are presented for the extreme case of free-molecule regime and thin plasma sheath. It has been shown that the existence of a temperature gradient in the plasma causes a nonuniform distribution of the local heat flux density on the sphere surface with its maximum value at the fore-stagnation point of the sphere, although the total heal flux to the whole particle is independent of the temperature gradient existing in the plasma. This nonuniform-distribution of the local heat flux density causes a nonuniform distribution of the. local evaporated-mass flux and related reaction force around the surface of an evaporating particle, and thus causes an additional force on the particle. Calculated results show that the thermophoretic force on an evaporating particle may substantially exceed that on a nonevaporating one, especially for the case of a metallic particle (with infinite electric conductivity). The effect of evaporation on the thermophoretic force is more pronounced as the evaporation latent heat of the particle material is comparatively low and as high plasma temperatures are involved.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01465745
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  • 8
    Digitale Medien
    Digitale Medien
    Unsteady heating of metallic particles in a rarefied plasma (1995)
    Springer
    Plasma chemistry and plasma processing 15 (1995), S. 199-219 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Metallic particles ; unsteady heating ; free-molecule regime ; analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Analytical results are presented concerning the unsteady heating of a metallic spherical particle innnersed in a rarefied plasma. The results show that the tinte periods required for the solid-phase heating, melting, liquid-phase heating, and evaporation are all proportional to the particle radius. For estimating the time needed for the solid-phase heating and that for the melting, the additional heat transfer rmechanism due to the thermionic emission front the particle surface is usually negligible since the surface temperatures of the particle heated in the plasma are, in general, compartively low during those heating steps. Thermionic emission assumes its effect only as the higher surface temperatures of the heated particle are involved (e.g., higher than 4000 K), while radiation loss shows its effects at much lower wall temperatures. As the plasma temperature is comparatively low, radiation heat loss may restrict the surface temperature of a particle to such a low value that the effect of thermionic emission on the overall heating time can he neglected and complete evaporation of refractor y metallic particles becomes impossible. The uncertainty in the calculation of the effect of thermionic emission is associated with the choice of the value of the effective work function for the particle material.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01459696
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  • 9
    Digitale Medien
    Digitale Medien
    Effect of the Knudsen number on heat transfer to a particle immersed into a thermal plasma (1983)
    Springer
    Plasma chemistry and plasma processing 3 (1983), S. 97-113 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Knudsen effect ; heat transfer ; small particles ; thermal plasmas ; analytical studies
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract The Knudsen effect on heat transfer to a particle exposed to a thermal plasma is important for many practical situations experienced in plasma chemistry and plasma processing. This paper provides theoretical results of this effect based on the “heat conduction potential jump” approach. It is shown that a correction factor which depends on the Knudsen number must be introduced into the expressions for heat fluxes obtained previously based on the continuum approach. The Knudsen effect is stronger for smaller particles and it is also more pronounced for an Ar-H2 plasma (compared to Ar and nitrogen plasmas at the same temperature). Since the Knudsen effect depends on the surface temperature of a particle, calculation of particle heating becomes more complicated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00566030
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  • 10
    Digitale Medien
    Digitale Medien
    Drag force acting on an evaporating particle immersed in a rarefied plasma flow (1995)
    Springer
    Plasma chemistry and plasma processing 15 (1995), S. 1-23 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Drag force ; evaporating particle ; free-molecule regime ; analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Analytical expressions are presented for the drag force acting on an evaporating or nonevaporating particle immersed in a plasma flow for the extreme case of free-molecule flow regime and thin plasma .sheath. It is shown that the drag force on a spherical particle is proportional to the square of the particle radius and to the relative velocity between the particle and the bulk plasma at low speed ratios. The existence of a relative velocity between the particle and the plasma results in a nonuniform heat flux distribution with its rnaximum value at the frontal stagnation point of tire sphere. This nonuniform distribution of the local heat fux density causes a nonuniforrn distribution of the local evaporated-mass flux and vapor reaction force around the surface of an evaporating particle, and thus induces an additional force on the particle. Consequently, the drag force acting on art evaporating particle is always greater than that on a nonevaporating one. This additional drag force due to particle evaporation is more significant for nonmetallic particles and for particle materials with lower latent heat of evaporation and lower vapor molecular mass. It increases with increasing plasma temperature and with decreasing gas pressure at the high plasma temperatures associated with appreciable gas ionization. The drag ratio increases with increasing electron/heavy-particle temperature ratio at high electron temperatures for a two-temperature plasma.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01596679
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