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Heat and Mass Transfer at Low Temperatures

Bernard Castaing
Laboratoire de Physique - ENS Lyon, 69007 Lyon, France

B. Hebral
CNRS-CRTBT, 166 X, 38042 Grenoble Cedex, France

A. Lacaze
CNRS-CRTBT, 166 X, 38042 Grenoble Cedex, France

Abstrakt

Cryogenists have always been challenged by the problem of heat transfer. In fundamental research the samples under investigation at temperatures below 10 mK are mostly the cold sources (3He, Cu, ...) and significant temperature differences are observed with the environment below 0.1 K. On the other hand large scale applications at cryogenic temperatures,as the operation of superconducting coils, need to extract powers up to 10 or 100 W which requires a specific approach just to insure the fiability of the system. Hopefully it turns out that low temperature heat transfer is by itself a specific research subject giving both a special insight into fundamental processes and very elegant technical solutions due to peculiar properties occuring only at low temperature.
As for any domain of temperature, heat can be transfered by radiation, conduction or convection. At liquid helium temperatures thermal radiation is negligible. Conduction and convection, besides the classical variation with temperature, present unusual properties characteristic of this temperature range: for instance mass transfer is not necessarily correlated with convection processes. Also it is possible to observe mass transfer without heat transfer as, at any temperature, heat transfer happens without mass transfer in heat conduction.
After a summary of classical heat conduction properties at low temperature, this paper will develop several low temperature specific cases of heat transfer, namely the properties of superfluid Helium, heat transfer at interfaces and some applications for ultra low temperature cooling as well as operation of superconducting coils. This study will be limited to the steady state regime.

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