Infrared analysis and pressure measurements on a single loop pulsating heat pipe at different gravity levels

A Single Loop Pulsating Heat Pipe (SLPHP) with an inner diameter of 2 mm is tested in hyper/micro gravity conditions during the 68th ESA Parabolic Flight Campaign. The system is designed with two sapphire tubes that connect the heated and the cooled section, allowing simultaneous fluid flow high-speed visualization, and a direct to fluid IR analysis by using respectively a high-speed camera and a Medium-Wave Infrared Camera (MWIR). Three independent heaters are positioned at the evaporator in order to vary the power distribution and to promote different flow motions with specific heating configurations. Furthermore, two highly accurate pressure transducers measure the pressure drop between the condenser and the evaporator. Additionally, twelve thermocouples mounted on the external tube wall record local temperatures during parabolic flight tests. Such a complete thermo-fluid dynamic analysis at different gravity levels, coupled with the acquisition of high-speed and infrared images in the transparent section of the SLPHP, has the main objective of providing a better understanding on the relationship between the fluid flow motion and the thermal response of the device. Infrared Time-space temperature maps of the flow are correlated with pressure measurements, the external wall tube temperatures, the liquid slug velocity and the local void fraction; providing an exhaustive overview of such a PHP transparent tube both in microgravity and hyper-gravity conditions. Additionally, for the first time in microgravity, the effect of the condenser temperature on PHPs is explored. When the condenser temperature is set at a higher value than the environment, results highlight that the possibility to invert the flow motion direction by means of non-symmetrical heating configurations is hindered. These experimental data could assist the development of improved numerical models of Pulsating Heat Pipes at different gravity levels.