Abstract
Experiments on helium-4 film flow over a stainless steel beaker rim have been carried out in the temperature region 11 mK to 1.63 K. A study of oscillation damping and low-velocity steady state flow provides the first evidence of dissipation at “subcritical” transfer rates below 1 K and suggests that a dissipation mechanism other than irreversible heat exchange between the bulk liquid reservoirs or the thermal nucleation of vortices and their subsequent transport across the stream is in operation. Flow experiments involving step-function changes in the chemical potential difference between the ends of the film confirmed the existence of a range of metastable “critical” transfer rates at all temperatures but failed to demonstrate a preferred rate structure. The variation of the mean critical rate with temperature corroborated the results of other workers above 36 mK and extended these measurements to lower temperatures.
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