• Pulsating Heat Pipe
• space applications
• start-up
• partial activation
• full activation
• infrared analysis

The thermal management system plays a key role in the field of space industry while designing a spacecraft for various stages of its life. The primary objective of the thermal subsystem is to maintain all the components inside the spacecraft within their operating temperature. Heat pipes are one of the most reliable and effective methods to manage the thermal issues which may occur during a spacecraft mission. The Pulsating Heat Pipes (PHPs) are a new and promising member of the wickless heat pipe family. It assures the current industrial demands such as efficient thermal control, durability, and low cost with high effective thermal conductivity and simplicity of construction. Even though many theoretical and computational studies have concentrated on PHPs in the last few decades, their Chaotic thermofluidic behaviour is still studied by researchers. The aim of the present work is to characterize a particular type of PHP for space applications by considering the effect of the gravity field and the condenser temperature.
In this experimental work, a 3D PHP previously design and built by the research group of the thermal physics laboratory of the University of Pisa in the framework of the European Space Agency (ESA) Microgravity Application Program (MAP) Project “Innovative Wickless Heat Pipe Technologies for Space and Ground Applications”, is tested on ground in horizontal, vertical Bottom Heated Mode (BHM) where the device operation is assisted by gravity and vertical Top Heated Mode (THM) mode in antigravity operation under the different heat input levels. The PHP is made of an Aluminium tube (inner/outer diameter 3 mm/5 mm) and bent in 14 turns filled with methanol (50% filling ratio). The PHP is built with a transparent sapphire tube inserted for visualization and IR imaging. The device is equipped with multiple wall thermocouples, two miniature pressure transducers, and two micro thermocouples for direct fluid measurement that provides a detailed insight into the thermodynamics behaviour of the device. A previously calibrated Medium Wave Infrared (MWIR) camera is employed to measure the external wall temperature within the PHP adiabatic section. The external tube surface is coated with a highly emissive black paint (global emissivity = 0.92), in order to provide further information about the PHP working regimes. For each PHP orientation and condenser temperature, the PHP different working regimes (i.e., start-up, full activation, stop-overs, thermal crisis) are recognized and studied for each power input given to the evaporator. In addition to that, the equivalent thermal resistance of the PHP is also evaluated to quantify the comparison between different operation modes and orientations. Results show that when the device is provided with medium/high heat fluxes and the condenser temperature is set to 20 °C, its thermal performance is not affected by the orientation with respect to gravity. This confirms the promising potential of this heat transfer device for space applications. Moreover, further investigations are needed into the actual weightlessness conditions (i.e., parabolic flights, ISS.) to improve the understanding of the PHP working behaviour.