Thermal Vacuum test of a Pulsating Heat Pipe Radiator for space application.

Heat transfer requirements in space are constantly growing as the electronics power consumption increases. Pulsating Heat Pipes (PHPs) are an efficient and totally passive way to transfer thermal power from the hottest components to the external radiator. Although PHPs have been extensively studied in the literature, the relative TRL is low for space applications. The low TRL is mainly due to a gap in the knowledge of standard testing procedures of radiative PHP in space environment. This thesis aims to testing a PHP radiator at boundary conditions typical of space thermal environment (low temperature and high vacuum). This work is the result of a collaboration between the Heat Transfer Laboratory at the University of Pisa and the Aerospazio Tecnologie srl company, whose core business is in the space environment simulation testing. An already existing device that was tested under forced convection during parabolic flights, has been modified to adapt it to the boundary conditions typical of space thermal environment. For this reason, the heat sink of the test cell has been modified in a radiator spreader, previously designed and optimized with a commercial Finite Element Code. A vacuum test facility was made available by Aerospazio Tecnologie srl. The modified test cell has been adapted to the thermal vacuum facility and an experimental campaign was designed and set up. Measurements of temperature and pressure have been acquired at different input powers (from 40 W up to 80 W) and at different sky temperatures (-60°C/-80°C/-100°C). The collected data has been compared to the radiator thermal simulations, coming from the previous finite element analysis, showing a good agreement. From the experimental campaign it results that a minimum power must be supplied to activate the efficient thermal PHP performance and the lower is the sky temperature the higher is the minimum activation power (80W for -100°C). The PHP can be deactivated by decreasing the power supplied and a really viscous blockage of the oscillating fluid has been observed. In conclusion, this work has been useful to define a standard experimental procedure to test the operative performance of a radiative PHP for space application. An unknown viscous blockage of the fluid oscillation has been observed at low temperature. It could be crucial for space missions because the PHP can’t operate at low input powers. A theoretical hypothesis to explain it has been proposed. A larger experimental and theoretical investigation of this phenomenon must be done in future in order to setup predictive model tools