Characterization of a hybrid closed loop thermosyphon : pulsating heat pipe for ground and space applications

A novel type of multi-evaporator Closed Loop Two Phase Thermosyphon/Pulsating Heat Pipe hybrid device has been designed for passive heat exchange and tested at different inclinations, heat input power and gravity field levels. The device consists in an aluminum tube, bent into the shape of a planar serpentine with five U-turns in the heated zone, with a transparent section in the condenser for the purpose of visualization. The tube is filled with FC-72 with a 50% filling ratio. Each evaporator turn is equipped with an electric wiring heater to simulate a thermal load and the choice of a specific location of the heating sections can induce the fluid to circulate regularly in a preferential direction. The experimental setup allows for temperature, pressure, acceleration and power supply readings and recording, as well as high-speed video capture on ground and in parabolic flight. The device’s performance and its operational limits have been tested on ground, in micro- and hypergravity conditions. In microgravity, the sudden absence of the buoyancy forces activates an oscillating slug/plug flow, allowing the device to work as a pulsating heat-pipe (PHP) also when horizontally placed. On the ground, the asymmetric heating placement proves to be a step forward in increasing the device’s operational stability and the maximum heat flux that can be introduced before incurring in a thermal crisis. The research objective is to contribute to the characterization of this relatively new kind of heat transfer solution, both for ground and space applications. The results described have been published in three academic papers, two of which were co-authored by the author of this thesis. A fourth paper is currently submitted for review to a scientific journal.