Cooling of long tube systems with superfluid helium

Heat transport experiments with superfluid helium in pipes of 60 to 400 cm length and diameters between 0.3 to 1.0 cm show the existence of a critical heat flow density, when superfluidity breaks down and vaporization onset starts. The critical heat flux is mainly determined by the amount of superheating required for bubble formation. Assuming that nucleation occurs on the superfluid vortex lines or vortex rings, the measured values of superheat can be explained