A Study of Some of the Parameters Affecting Knudsen Effusion Deviations from the Cosine Law as a Function of Cell Geometry, Cell Materials, and Nature of the Effusing Species

摘要

Experimental studies of the distributions of particles effusing from a Knudsen cell at high temperatures (1000 - 2000°K) reveal marked deviations from the cosine law. It would appear that complete thermo-dynamic equilibrium is seldom achieved in a high-temperature Knudsen experiment;further, in terms of ordinary kinetic theory, descriptions of the behavior of the "gas" inside the cell are oversimplified. The measured distributions show clearly, in a fashion analogous to the formation of an image by a pinhole camera, the effects of geometry and choice of materials for each Knudsen cell. In particular, con¬tainment problems which force the use of special cell materials at high temperatures may introduce side effects which can cause serious deviations from theory.