Effects of Deviations from Isothermal and Quiescent Conditions on the He II Film Transfer Rates

Abstract

We have studied the effects of temperature differences between and mechanical agitation of the source and sink bulk liquids on the volume rates of transfer of liquid He II through the film into and out of a glass capillary beaker over heights to 31 cm. Temperature differences were produced by electric heaters, and mechanical agitation was produced by using a magnetic field modulated at a low frequency to cause a 1-mm diameter superconducting sphere to undergo translational oscillation. Values of heat flux up to ${10}^{\ensuremath{-}4}$W/${\mathrm{cm}}^{2}$ produced only temperature differences which could be accounted for by distillation and thermomechanical effects. Such quantities of heat flux do not create sufficient turbulence to produce measurable effects on the transfer rates. Mechanical agitation of the source liquid increased the transfer rates, and agitation of the sink liquid decreased the rates. A minimum velocity of the sphere moving in the liquid was required to produce any measurable change $\ensuremath{\Delta}R$ in the transfer rates. After increasing with increasing velocity of the sphere, $R$ was found to become independent of further increases in velocity. These results give further insight into the way in which transfer rates of liquid helium through the film depend on the state of turbulence of the bulk liquids which serve as the source and sink for the film.