Thermodynamics of Superflow in the Helium Film

The saturated superfluid film is capable of acting as a siphon, allowing the superfluid to drain out of any containing vessel to find the lowest available gravitational level. As in any siphon, the pressure in the film is lower when it is flowing than when it is at rest, owing to the Bernoulli effect. Since the film has a free surface which presumably cannot support a pressure discontinuity, it was expected that the flowing film would collapse on itself, like a siphon with flimsy walls. In particular, at typical film flow velocities a reduction in thickness of about one-quarter was expected