Published online by Cambridge University Press: 21 April 2006
The results of a theoretical investigation of the low-speed motion of a volatile spherical particle in its saturated vapour at arbitrary values of the Knudsen number, evaporation coefficient and tangential momentum accommodation coefficient are presented. The problem is solved on the basis of the Bhatnagar, Gross & Krook (1954) linearized kinetic equation with the model collision integral. The variational method developed for the solution of the axisymmetric problems (Cercignani & Pagani 1968) is employed to calculate the drag. Phase changes on the particle surface have been shown to reduce the drag by an order depending on the Knudsen number. Incomplete accommodation of molecules colliding with the particle also results in the reduction of the drag over the whole range of Knudsen numbers.