On the irreversible processes in liquid helium II

Abstract It is pointed out that the two-fluid model can account for a number of the peculiar properties of liquid helium II. An attempt is made to use this model, in the form proposed by T i s z a, for an analysis of the heat flows in slits and capillaries. A l l e n and R e e k i e's rule that heat flow and fountain effect are proportional is explained, and from the proportionality constant for rather narrow slits the viscosity of the normal fluid is calculated. The calculated values are found to be in agreement with those obtained from oscillating disc experiments. If the two fluids move with respect to one another a mutual friction appears to occur which, in first approximation, is proportional to the cube of the mutual velocity. Assuming this, the equations of motion for the two fluids are given in addition to a series of formulae and predictions about heat flow, flow of matter, mechano-caloric effect and the extinction of temperature waves (second sound). A more careful examination of the experimental data reveals that the heat flow in capillaries of 1 micron and narrower is larger than expected. This may perhaps be due to a mean free path effect in the normal fluid. The proportionality of the mutual friction with the cube of the relative velocity is not too well realised in wide capillaries at the higher velocities. This might perhaps be ascribed to turbulence effects in the superfluid phase which was supposed to have zero viscosity.

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