Flow of Liquid Helium II

Abstract

A SURVEY of the various properties of liquid helium II has prompted us to investigate its viscosity more carefully. One of us1 had previously deduced an upper limit of 10−5 C.G.S. units for the viscosity of helium II by measuring the damping of an oscillating cylinder. We had reached the same conclusion as Kapitza in the letter above ; namely, that due to the high Reynolds number involved, the measurements probably represent non-laminar flow. Evidence for the existence of an unusual liquid phase of 4He below about 2.2 K — the 'λ-point' — can be traced back to 1911 and the experiments of Kamerlingh Onnes. But it was another two decades before a clear picture started to emerge concerning the 'superfluid' nature of this phase. Key to establishing the concept of superfluidity were the measurements of Kapitza and Allen and Misener in 1938, which showed that the viscosity of 4He dropped to essentially unmeasurable values when cooled below the λ-point. [Obituary of Jack Allen: Nature 411, 436 (2001)]