Experimental validation of Large Diameter PHP numerical simulation in Microgravity environment

A large diameter PHP is a particular device operating as Thermosyphon on ground and as a PHP in microgravity conditions. In microgravity environment the ratio between buoyancy forces and surface tension forces decrease, allowing to exploit larger diameter tubes with respect to the capillary limit on ground. A slug/plug flow pattern, typical of a PHP device, is therefore observed in microgravity conditions Different kind hybrid Loop Thermosyphon/Pulsating Heat Pipe devices has been already tested in previous experimental campaign (parabolic flights and sounding rocket). It has been noted that as the microgravity occurs a flow pattern transition from a stratified to a slug-plug regime is clearly observed and simultaneously the flow pressure signal exhibits an oscillating trend. It is kept throughout the entire 0-g period. A new hybrid LT/PHP has been tested during the 67th ESA parabolic flight campaign. The device has been tested in vertical position, bottom heated mode, at eight different power levels (18, 36, 52, 68, 96, 134, 146, 180 W) investigating both the thermal performances and the start-up during the microgravity period. A greyscale and SW IR visualizations have been performed during the entire test period joined with pressure and temperature high frequency signals acquisition. This paper shows the thermal and dynamic analysis of the liquid slugs over time along the microgravity period. In particular it has been measured: the meniscus velocities, the liquid slug lengths and the temperature gradient along the liquid slug over time. They have been correlated with the pressure and temperature signals at the evaporator and the condenser. All the data has been compared with the numerical simulations coming from CASCO model.