PHOS EXPERIMENT: THERMAL RESPONSE OF A LARGE DIAMETER PULSATING HEAT PIPE ON BOARD REXUS 18 ROCKET

A Pulsating Heat Pipe (PHP) is a two-phase passive heat transfer device that may be proved suitable for the thermal management in space applications. A recent parabolic flight experiment has already highlighted that a capillary tube PHP has the same thermal performance either on low gravity environment or on ground with the evaporator and condenser placed horizontally with respect to the gravity vector. An increase of the inner tube diameter theoretically may lead to an increase of the thermal performance but it is only achievable in the presence of low gravity conditions. In the present study, the experimental results of two PHPs tested on board REXUS 18 rocket are presented. The PHPs are both filled with the refrigerant FC-72 and have an inner tube diameter larger than the critical diameter (3 mm) and around the critical diameter (1.6 mm), respectively. In the occurrence of the milli-gravity conditions experienced on board the rocket, surface tension prevails over buoyancy and the flow pattern inside the devices should switch to the slug and plug PHPs typical operational regime. The temperature and pressure trends are expected to reveal such a regime transition and provide further information for future developments. The tested PHPs consist of a closed end-to-end aluminium tube with fourteen curves arranged on two planes constituting the evaporator or hot section. The heat input is supplied by two heating cables wound around the tube and placed asymmetrically with respect to the curves, so as to promote the fluid circulation in a preferential direction. The heat input value has been selected in order to have the same heat flux at the evaporator section in both situations. The heat is transferred through the devices and, at the end, released in a phase change material via latent heat of fusion without any appreciable temperature buildup for the entire duration of each experimental run.