Transient heat transfer into liquid helium I

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Abstract
We have investigated the transient transfer of heat from a crystal of bismuth into a bath of liquid helium I in response to a step-function current applied to the crystal. The superheat temperature ΔT of the helium in contact with the crystal was monitored through the magnetoresistance of the bismuth which is strongly temperature dependent at liquid-helium temperatures. It is found that as a function of time, the transient superheat temperature can rise above (i.e., ’’overshoot’’) its steady-state value. Of particular interest is the fact that, within a certain range of bath temperatures and heat fluxes, these transient overshoots develop quite sharp peaks at a superheat temperature ΔTmc which is independent of the applied heat flux. This overshooting of the transient superheat temperature is discussed in terms of the delayed onset of nucleation. In particular, it is suggested that the sharp overshoots result from the rapid onset of homogeneous nucleation. The temperatures associated with the sharp overshoots are compared with theoretical estimates of the homogeneous nucleation temperature for liquid helium.

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