Heat transfer to a single particle injected into a thermal plasma

This paper is concerned with the study of the heat transfer between a thermal plasma and a particle injected into it, with emphasis on the effects which the evaporation of the latter imposes on heat transfer from the former. The investigation was done by numerical methods. The results refer mainly to an atmospheric pressure argon plasma. As a comparison nitrogen plasma was considered in a temperature range from 3000 to 25,000 K. Interaction of plasma with alumina and tungten particles were considered. Evaporation severely reduced heat transfer to a particle and, in general, this effect was more pronounced for materials with low latent heat of evaporation. The conductive heat transfer from plasma (Ar, N-2, Ar + H-2) to a particle of radius 50 mu m was calculated and compared with the radiative heat loss from the particle. The results of a relatively simple analysis showed that except for a particle with a surface temperature above 2100 K immersed in an argon or a nitrogen plasma below 4100 K, radiation heat losses from the particle to the surroundings are negligible compared to the conductive heat flux from plasma to the particle. The minimum value of plasma temperature for a particle to attain boiling point was calculated. The calculated results for the lowest value of plasma temperature for the three materials (Alumina, Tungsten, Graphite) and four plasmas (Ar, N-2, H-2, Ar + H-2) are reported. The plasma temperature is higher for higher boiling paint materials and lower for higher enthalpy plasmas. (C) 1999 Elsevier Science B.V. All rights reserved.