Heat conduction through narrow channels and phase separation of He II at zero gravity

Abstract

We explain the heat flow properties of a system which works as a phase separator for superfluid helium at zero gravity. Differently from most previous work the flow of He II in a narrow slit between a helium bath and a vapour space (instead of a second He bath) is studied. Due to the Fountain effect most of the He II stays contained in the bath, and a small amount is evaporated to carry away the heat transported through the slit. The role of evaporation kinetics is discussed and its contribution, raising the heat flow resistance, is calculated. At higher heat flow there is a sharp transition to a different flow state, which we identify with the Gorter-Mellink regime where the supercomponent flows dissipatively and liquid enters into the vent line so that an additional heat exchanger is necessary for its evaporation. In this regime the mass and heat flow are still controlled by the applied pressure gradients or-important for practical use:-by varying the length of the slit.