(658a) Knudsen Permeability of Fibrous Films

Knudsen transport occurs either at low pressures. or within the void space of a finely dispersed solid at normal pressures. Rigorous, analytical permeability results for porous, fibrous films of finite thickness are derived from variational principles and scattering theory. The fiber beds are modeled by randomly placed cylinders with several orientations. The development of the Knudsen flow equations for a porous, fibrous film is a classical problem with a variety of potential applications. The results apply to transport within the columnar structure, characteristic of thin films deposited by sputtering or evaporation. They also provide permeability models for transport across membranes, and streached polymer films. The equations can be used to treat edge effects in fiber preforms during the chemical vapor deposition manufacture of fiber composites.