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  • free-molecule regime  (5)
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  • 1
    Electronic Resource
    Electronic Resource
    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
    Keywords: Thermophoresis ; evaporating particle ; free-molecule regime ; analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01465745
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  • 2
    Electronic Resource
    Electronic Resource
    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
    Keywords: Drag force ; evaporating particle ; free-molecule regime ; analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01596679
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    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
    Keywords: Metallic particles ; unsteady heating ; free-molecule regime ; analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01459696
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  • 4
    Electronic Resource
    Electronic Resource
    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
    Keywords: Thermophoresis ; free-molecule regime ; analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01447030
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  • 5
    Electronic Resource
    Electronic Resource
    Thermophoretic Force on a Small Particle Suspended in a Plasma with a Combined Specular and Diffuse Reflection at the Particle Surface (1999)
    Springer
    Plasma chemistry and plasma processing 19 (1999), S. 33-51 
    Details
    ISSN: 1572-8986
    Keywords: Thermophoresis ; nonevaporating or evaporating particle ; free-molecule regime ; combined specular and diffuse reflection ; sphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Additional kinetic-theory analytical results are presented concerning the thermophoretic force acting on a spherical nonmetallic or metallic, nonevaporating or evaporating particle suspended in a plasma for the extreme case of free-molecule regime and thin plasma sheath. A combined specular and diffuse reflection of the atoms incident on or formed in the ion–electron recombination process at the particle surface has been taken into account in this analysis as an extension of the previous paper (Xi Chen, J. Phys. D: Appl. Phys. 30, 826–841, 1997). It has been shown that the specular reflection fraction of gas particles at the surface does not affect the thermophoretic force acting on a nonevaporating, metallic or nonmetallic, spherical particle, but they affect significantly the evaporation-added thermophoretic force. The evaporation-added thermophoretic force decreases linearly with the increase of the specular reflection fraction, and the decreasing rate for a nonmetallic evaporating particle is much greater than that for a metallic one at high plasma temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021851815657
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    Paper (German National Licenses)
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