Bifluid dual core heat pipe: conducting heat from 150 to 350 K

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Bifluid dual core heat pipe: conducting heat from 150 to 350 K

Demolder, B. / Voyer, E. / Briet, R.

Heat pipes can be filled with various fluids in order to adapt their temperature range or their heat transport properties to the requirements. Unfortunately, low temperature heat pipes can hardly start at room temperature under realistic heat loads due to their poor heat transport capability in this temperature range. This paper describes an innovative way to start a low temperature heat pipe from room temperature and to enlarge the operational range by associating a second core with another fluid in parallel. A 1.6 m long dual channel axially grooved heat pipe has been filled with ammonia for one core and with ethane for the other one. Tests have been performed at ALCATEL SPACE in Cannes, France, and at CNES in Toulouse, France, above and below the freezing point of ammonia (195 K). Heat transport capability has been measured and is compared to simulations in the 150-350 K range. A minimal heat transport capability of 30 W/m under 0 mm tilt is found over the entire temperature range. Functional test performed on the entire temperature range shows a progressive transition of heat transport from ethane to ammonia during warm up and from ammonia to ethane during cool down. This transition arises without noticeable change in the thermal gradient across the heat pipe. This bifluid dual core heat pipe can hence be used to cool a low temperature device starting from room temperature or to allow a uniform thaw of a frozen ammonia heat pipe. This successful characterisation allows to examine some industrial aspects of this product and to propose a qualification program for this kind of heat pipe.