title: Drag force, diffusion coefficient, and electric mobility of small particles. I. Theory applicable to the free-molecule regime.
abstract: The transport of small particles in the free-molecule regime is investigated on the basis of gas kinetic theory. Drag force formulations were derived in two limiting collision models-namely, specular and diffuse scattering-by considering the potential force of interactions between the particle and fluid molecules. A parametrized drag coefficient equation is proposed and accounts for the transition from specular to diffuse scattering as particle size exceeds a critical value. The resulting formulations are shown to be consistent with the Chapman-Enskog theory of molecular diffusion. In the limit of rigid-body interactions, these formulations can be simplified also to Epstein's solutions [P. S. Epstein, Phys. Rev. 23, 710 (1924)].
authors.affiliation: Department of Mechanical Engineering, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Li
authors.forename: Hai
authors.initials: H
authors.lastname: Wang