THERMOPHORETIC FORCE ACTING ON AN EVAPORATING PARTICLE SUSPENDED IN ARAREFIELD PLASMA

Analytical results of the thermophoretic force on an evaporating spher ical particle immersed in a rarefied plasma with a large temperature g radient are presented for the extreme case of free-molecule regime and thin plasma sheath. It has been shown that the existence of a tempera ture gradient in the plasma causes a nonuniform distribution of the lo cal heat flux density on the sphere surface with its maximum value at the fore-stagnation point of the sphere, although the total heat flux to the whole particle is independent of the temperature gradient exist ing 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. Calcula ted results show that the thermophoretic force on an evaporating parti cle may substantially exceed that on a nonevaporating one, especially for the case of a metallic particle (with infinite electric conductivi ty). The effect of evaporation on the thermophoretic force is more pro nounced as the evaporation latent heat of the particle material is com paratively low and as high plasma temperatures are involved.