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Explanation for the Fountain effect in superfluids

  1. Apr 14, 2010 #1
    I'm looking for an explanation for the fountain effect in superfluids using the 'two fluid model'. However the explanations I've come across are not very satisfactory

    From the NASA website

    http://cryo.gsfc.nasa.gov/introduction/liquid_helium.html

    But why does superfluid Helium flow from cool areas to warm areas? Unless I'm missing something that it is not a property of all fluids is it? The wiki article on Helium says

    But I don't see why the system needs to maintain the same fraction of superfluid helium. Surely at higher temperatures there is a lower equilibrium fraction of superfluid.
     
  2. jcsd
  3. Apr 15, 2010 #2
    The analogy is that of partial pressure. Like with osmosis you get osmotic pressure if you have an uneven concentration of some salt. If you have an uneven concentration of suprafluid helium it is the same
     
  4. Nov 11, 2011 #3
    Yes, this fact is known. Even Feynman couldn't explore theory of superfluidity in details.
    You can see his book on statistical mechanics (last edition) and see that Feynman suggest to publish anybody paper explaining lambda point curve in He4. He couldn't get second order phase transition curve himself (only third order phase transition for Bose codensation).

    I also remember, that Feynman main paper on superfluidity didn't deal with the fountain effect. So we don't have so genius author to explain fountain effect now to all of us.

    But at the same time we can find such instability in plasma and/or in hydrodynamics as "negative energy wave" (we can google out topical reviews on such instabilities). This instability is famous for moving frames could diminish total energy of the system. So "moving frame" (in our case "superfluid" fraction of He4 can fontain at the expense of total energy.
     
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