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Why does zero viscosity allow superfluids to climb?

  1. Feb 28, 2009 #1
    Since there are no frictional forces acting on the superfluid my intuition would tell me that there is no way for the liquid to "climb" the sides of a container. Obviously though, intuition isn't the best thing to go by when it comes to superfluids. I'm just wondering: what mechanism drives it to climb up when there's no fluid there in the first place?

    A slightly different question and one that is always met (and for good reason) with large amounts of skepticism, is perpetual motion. I was reading about superfluids and came across the idea that if you had a superfluid spinning in a container it would spin indefinitely. Is this kind of perpetual motion possible other then the fact that you have to keep the substance at a very low temperature?
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  3. Mar 1, 2009 #2

    Vanadium 50

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    What makes you think there's no fluid on the sides of the container?

    As far as your second question, do you know what perpetual motion machine is? It's not something moving perpetually; it's extracting energy from a closed system.
  4. Mar 1, 2009 #3
    I had heard that if the container was not sealed the superfluid would move into a lower container. So I figured that meant it must not require there to be the substance on the sides of the container in the first place allowing it to climb up. However, I may have just heard wrong or where I heard it from might have not been saying it exactly as is scientifically true. Does it require small amounts of the superfluids to be there in the first place?

    As for the definition of perpetual motion, as far as I've seen it's just a device that will continue to operate without the introduction of energy from an external force. Most likely though you know more about it then I do. But it's true that the superfluid would keep spinning forever right? Or is there some other mechanism that would stop it?
  5. Mar 2, 2009 #4

    Vanadium 50

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    There are small amounts of superfluid on the edge. You have evaporation and you have condensation, right? Hence my question - why do you think there's no fluid on the sides of the container?
  6. Mar 2, 2009 #5
    There is no resistance to flow (zero viscosity). The fluid must be less dense than the surrounding fluid for it to climb the walls (Archimedes).
  7. Mar 7, 2009 #6
    Keep in mind several things:

    - The energy reguired to lower a temperature to that degree.
    - The energy required to keep a superfluid at that temperature during physical energy extraction.

    So, is it possible to extract energy from the superfluid phenomenon itself? Yes! Of course!!

    Does the possible energy extracted equal or exceed the energy required to allow the superfluid phenomenon to occur and maintain itself? No.
  8. Mar 14, 2009 #7
    The superfluidity is analogues to ferromagnitism. It is more favorable (energetically) to get to motion in some direction, than to be calm (V=0).

    So it is the answer :)
  9. Mar 16, 2009 #8
    The mechanism of climbing fluidity is in fact very simple: the gravity. Suppose some Helium superfluid is held in a glass. Now it has a finite liquid column height, which means a gravitational potential. Now let's imagine the column is as stacked from thin layers, upper ones pressing lower ones due to gravity. Therefore, the bottom layer shall be pushed and will climb along the cup wall to escape the pressure if no friction exists. That is why superfluidity climbs. It does so and its potential energy lowers.

    The above idea can be easily tested by holding a cup of Helium in a free fall lift. No climbing should happen in this case.
  10. Mar 17, 2009 #9

    Vanadium 50

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    Um...potential energy is still mgh, no?

    If you look at a container of superfluid helium (not so easy - there is fog and frost seemingly everywhere) you will see that the fluid layer covers the outside as well, so you end up essentially with a siphon. The helium flows up initially but eventually ends up lower.
  11. Mar 17, 2009 #10
    What I want to emphasize is that, the force driving the climbing is the gravity, while potential energy lowering is a consequence.
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