Flow and Self-Diffusion of Gases in Capillaries. Part I

A model is presented for describing transport under a partial pressure gradient (self-diffusion) as well as transport under a total pressure gradient in capillaries of arbitrary length-to-radius ratio over a pressure range extending from the free molecule to the continuum regimes. The model provides a unified description of the transport and yields the same results as existing theories in the limited ranges appropriate for their application.