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  • 1
    Electronic Resource
    Electronic Resource
    Heat transfer to a single particle exposed to a thermal plasma (1982)
    Springer
    Plasma chemistry and plasma processing 2 (1982), S. 185-212 
    Details
    ISSN: 1572-8986
    Keywords: Heat and mass transfer ; small particles ; thermal plasmas ; exact and approximate solutions ; analytical studies
    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 This paper is concerned with an analytical study of the heat and mass transfer process of a single particle exposed to a thermal plasma, with emphasis on the effects which evaporation imposes on heat transfer from the plasma to the particle. The results refer mainly to an atmospheric-pressure argon plasma and, for comparison purposes, an argon-hydrogen mixture and a nitrogen plasma are also considered in a temperature range from 3000 to 16,000 K. Interactions with water droplets, alumina, tungsten, and graphite particles are considered in a range of small Reynolds numbers typical for plasma processing of fine powders. Comparisons between exact solutions of the governing equations and approximate solutions indicate the parameter range for which approximate solutions are valid. The time required for complete evaporation of a given particle can be determined from calculated values of the vaporization constant. This constant is mainly determined by the boiling (or sublimation) temperature of the particles and the density of the condensed phase. Evaporation severely reduces heat transfer to a particle and, in general, this effect is more pronounced for materials with low latent heat of evaporation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00633133
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Unsteady heating and radiation effects of small particles in a thermal plasma (1982)
    Springer
    Plasma chemistry and plasma processing 2 (1982), S. 293-316 
    Details
    ISSN: 1572-8986
    Keywords: Heating ; melting ; and evaporation of particles ; radiation effects ; analysis ; computation
    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 Based on exact solutions for the heat flux to a particle exposed to a thermal plasma given in a previous paper, initial unsteady heating (including heating of the solid phase, melting of the solid phase, heating of the liquid phase, and evaporation) and radiation effects are considered. Closed-form solutions can be obtained for particles with infinite thermal conductivities. The results show that the time periods required for the various steps are all proportional to the square of the particle radius, suggesting that reduced time periods which are independent of the particle radius are appropriate bases for comparison. Results are presented for three materials (alumina, tungsten, and graphite) and three types of plasmas (argon, argon-hydrogen mixture, and nitrogen). It is shown that evaporation (or sublimation) is by the slowest step among all processes in a plasma reactor if complete evaporation (or sublimation) of the particles is desired. Studies of the temperature history of particles with finite thermal conductivities show that temperature gradients within the particles depend on the ratio of the particles' thermal resistance to that of the plasma. In spite of the difference in initial heating, the analytical expressions based on infinite thermal conductivities predict the correct total time spent for both heating and evaporation even for low-conductivity materials such as alumina. The effect of radiation losses from a particle during heating becomes important for large particles, for high-boiling-point materials, and for low enthalpy differences between the plasma and the particle surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566525
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Behavior of small particles in a thermal plasma flow (1983)
    Springer
    Plasma chemistry and plasma processing 3 (1983), S. 351-366 
    Details
    ISSN: 1572-8986
    Keywords: Small particles ; heat transfer ; drag ; Knudsen effect ; convection ; thermal plasma ; computation
    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 In this paper computational results are presented which reveal the effects of the Knudsen number on heat transfer and drag of small particles in a flowing thermal argon plasma. The Knudsen number is restricted to moderate values so that “temperature jump” and “velocity slip” conditions may be employed, and for the governing equations the continuum approach remains valid. It is shown that the ratio of the heat fluxes with and without the Knudsen effect is almost identical to the ratio obtained by the authors for the case of pure heat conduction. This fact is very important for modeling of the behavior of particles injected into an actual plasma reactor when the Knudsen effect has to be taken into account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00564633
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    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
    Keywords: Knudsen effect ; heat transfer ; small particles ; thermal plasmas ; analytical studies
    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 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566030
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    Paper (German National Licenses)
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