Monte Carlo Simulation of Specular and Surface Diffusional Perturbations to Flow from Knudsen Cells

Abstract

Computer simulation of real experiment by Monte Carlo techniques has been used to study the behavior of particulate fluxes in Knudsen cell orifices. Two types of interaction with the interior and exterior surfaces of the cell lid and with the orifice wall have been predicted to cause deviations from Knudsen flow. The first is concerned with low-angle specular reflection in cylindrical orifices. The second perturbation results when a particle, upon striking a surface, is momentarily adsorbed and migrates to another location before being reemitted. Effects arising from these two types of perturbations have been analyzed as a function of the length-to-radius ratio of the orifice. Precise steady-state values were obtained for transmission coefficients, flux gradients on the surface, and spatial distributions of effusate.