Diffusion in rare-gas liquids : an experimental study

Abstract

This thesis describes the design and development of an apparatus for measuring the diffusion coefficients of cryogenic liquids. The diaphragm cell method is used. The experimental apparatus has a facility for the continuous monitoring of a radioactive tracer which is diffusing across a sintered stainless steel diaphragm. A scintillation counter assembly consisting of a cesium iodide crystal, a lucite light guide and a photomultiplier tube is used for this purpose. A temperature control method is incorporated which is capable of maintaining a set temperature to within ± 0.03 K in space and time. Modified equations for the diaphragm cell are derived for the case of continuous monitoring. It is shown that neither the initial concentrations of the two compartments of the cell nor the exact starting time of diffusion are necessary to compute the diffusion coefficient. The apparatus is used to measure the tracer diffusion coefficients of krypton in liquid argon over a temperature range of 85 - 103 K. The present data are discussed in relation to some other experimental and computer simulation results.