EXPERIMENTAL STUDIES OF HELIUM VAPOR REFLUXING IN NARROW TUBES

We report the results of pressure, temperature, and isotopic concentration measurements in tubes lined with a thermally driven, flowing superfluid film. For pure He-4 films, vapour refluxing generates gradients in both pressure and temperature. With the addition of a few percent of He-3, pressure gradients are dramatically reduced and the refluxing of He-4 atoms in the vapour couples gradients in temperature and isotopic concentration. We have observed that the He-3 concentration at the hot end of a narrow tube can be decreased by a factor greater than 10(4). These results can be interpreted in terms of a recently developed model which includes a description of the hydrodynamics of the refluxing vapour.