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.
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Keller, W.E., Hammel, E.F.: Annals of Physics10, 202 (1960)
Denner, H.D., Klipping, J., Klipping, G., Lüders, K., Menzel, J., Ruppert, U.: Proc. ICEC 7, IPC Science and Technol. Press, Guildford, U.K. 1978, p. 240 and Adv. Cryog. Eng. 25 (1980); see also: Seidel, A.: The German Infrared Laboratory, its overall concept and cooling system, Proc. ICEC 8, IPC Science and Technol. Press, Guildford, U.K. 1980, p. 43
For very narrow flow channels, say around 1 μm, which have near superleak properties, and very low temperatures the heat conductivity of the material contributing significantly and the helium itself begins to show peculiar heat conduction properties, see: Schmidt, R., Wiechert, H.: Z. Phys. B36, 1–12 (1979)
This means, contrary to the usually considered zero net mass flow arrangements, that some mass, the vapour, escapes at velocityv
For a review of different approaches to the evaporation kinetics problem see: Wiechert, H.: J. Phys. C9, 553 (1976). In this paper we deduce the evaporation rate in a different way
Gorter, G.J., Mellink, J.H.: PhysicaXV; 285 (1949). The Gorter-Mellink friction is dealt with in standard textbooks about helium, in our context see alse [1]
Over the past decades extensive work has been done by the Leiden group, (Kamerlingh Onnes Lab); of review character is: A synthesis of flow phenomena by: Haas, W. de, Beelen, H. van: Physica83B, 129 (1976); For a recent study of the mechanisms involved see: Yarmchuk, E.J., Glaberson, W.I.: J. Low Temp. Phys.36, 381 (1979)
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Attempts of measuring the hydrodynamic lengths of the slit by Poiseuille flow of air or cold He-gas always give the following tendency: the nominal lengths 0,2...0,8 cm seem too short (flow resistance was too high), the longest 1,4 cm seems somewhat too long, the same tendency is seen in Gorter-Mellink flow regime (see Figs. 3 and 4). Sincep i is not measured at the end of the slit but at the end of the vent line the flow independence of which is not known, it is difficult to make quantitative predictions about effects of the slit geometry like end effects or tilting of the cylindrical core. Experiments of clarify the situation are on the way
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Schotte, U., Denner, H.D. Heat conduction through narrow channels and phase separation of He II at zero gravity. Z. Physik B - Condensed Matter 41, 139–145 (1981). https://doi.org/10.1007/BF01293412
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DOI: https://doi.org/10.1007/BF01293412