The Two Fluid Model of the Helium Film

Abstract

Motivated by the recent discovery that the thickness of a helium film is independent of its state of superflow, we have analysed the conditions under which the two fluid model is consistent with equilibrium between film and vapour. The experimental result is found to be a natural consequence of the requirements for equilibrium. In addition we find that waves in a moving film should be convected at approximately 1/2(ρ_s/ρ) u_s, where u_s is the superfluid velocity. A new criterion for critical velocity is discovered and a new result is obtained for the attenuation of waves.

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