Shutdown Characteristics of an Axial-Groove Liquid-Trap Heat-Pipe Thermal Diode

The shutdown characteristics of an axial-groove liquid-trap heat-pipe thermal diode made of aluminum and using ammonia as the working fluid have been theroretically and experimentally determined. The heat-pipe diode has a total length of 470 mm and an outside diameter of 10 mm (the trap dimensions are 70 mm long and 25 mm outside diameter). The shutdown technique employed consisted of heating the condenser by applying a constant heat input while having the evaporator and trap, both thermally coupled to an aluminum thermal mass, thermally free-floating. The required shutdown energy (approximately 1.2 W.h) came very close to the theoretical minimum shutdown energy of 1.48 W.h, indicating no back-piping action during shutdown. The shutdown times were strongly dependent on the shutdown power applied. They varied between about 30 and 7 min for shutdown powers of between 5 and 15 W.