04 octobre 2011

The distribution of cold power in cryogenic systems is becoming increasingly important, in particular because of the replacement of cryogen baths by mechanical cryocoolers which are local cold sources. Two-phase systems (heat pipes) are good candidates to address this new problem. The SBT has designed, manufactured and tested a cryogenic pulsating heat pipe (PHP) that uses helium as a working fluid.


For distances greater than several meters, metallic thermal straps made of copper, aluminum, etc. have mediocre conduction over mass ratios. Thermal links that use a two-phase liquid vapor fluid circulation are attractive. Among them, the PHP has an efficient thermal performance. The laboratory prototype is a simple small and sealed pipe partially filled with liquid helium. The tube is bent into several turns (5 for this prototype, see Fig.) between the condenser (the cold point) and the evaporator, where the object to be cooled is located. The tube diameter must be chosen so that a series of liquid slugs and vapor bubbles can form inside the tube. The heat transfer between helium, the condenser and the evaporator leads to self-sustained oscillations between the two ends of the PHP. These oscillations provide for an efficient heat transfer with a complex mechanism. Good thermal performance is achieved with a 0.4 K temperature difference at 4.2 K and for 145 mW transferred heat power. Our prototype is 10 cm long, but could be longer. The cooling down time of a PHP alone as presented in the diagram takes 9 hours, which is still very long. But SBT already have the solution: stay tuned…


Maj : 17/02/2014 (938)


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