Transient heat transfer into liquid helium I

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.

Studies of nucleation and heat transfer in liquid helium isotopes 3 and 4

“…The thermometer response time is less than 100 us so the temperature excursions on a millisecond time scale are easily measured and reproduced. Complete details of the bismuth thermometer and the associated electronic circuitry have been published elsewhere (Brodie 1977(Brodie , 1978(Brodie , 1981. this difference in slope is proportional to the increased heat flux due to the light.…”

“…Our measurements were made using the technique of transient superheating pioneered by Brodie (Brodie 1977(Brodie , 1978(Brodie , 1981 and used by Sinha (1982b). However our experiments differ in some important ways from this technique.…”

“…Complete details of the bismuth thermometer and its associated circuitry can be found elsewhere (Brodie 1977(Brodie , 1981). Because of its small heat capacity and large coefficients of thermal conductivity and diffusivity, bismuth is ideally suited to this type of transient thermometry.…”

Studies of homogeneous nucleation and transient heat transfer in cryogenic liquids

“…The crystal resistance R1 depends on the applied magnetic field, the angular orientation of the crystal in the magnetic field, and the crystal temperature. Although our previous work (Brodie et al 1977) has only involved the temperature response to a step-pulse heating current, we expect that other functions of current (e.g. ramp, exponential, etc.…”