Effects of filling ratio of a long cryogenic Pulsating Heat Pipe

Abstract

In the development of cryogenic pulsating heat pipes for cooling superconducting devices, numerous progressive heat load tests have been performed at different filling ratios with neon, argon and nitrogen as working fluids. The tests have been carried on with a pulsating heat pipe system connected to an external buffer volume during the entire test (open configuration) and with the pulsating heat pipe system isolated from any external volume (closed configuration). From this two group of tests, it has been possible to determine the minimum filling ratio required to operate in stable conditions and also to determine the optimum filling ratio giving the highest thermal performance of the system for each working fluid. This filling ratios are always below 50%, revealing the key role of the fluid flow circulation in pulsating heat pipes, mainly ensured by the expansions and contractions of the vapor parts, in the global heat transfer. In addition, the analysis of the temperatures and pressure evolution of a progressive heat load test with a high filling ratio reveals that an excess of liquid impedes the flow circulation and therefore reduces the heat transfer from the evaporator to the condenser of the pulsating heat pipe. • A cryogenic Pulsating Heat Pipe has been tested with nitrogen, neon and argon. • Filling ratios ranging from 20 to 90% have been tested. • Progressive heat load tests have been performed in open and closed configuration. • Optimum filling ratios giving the highest thermal performance have been identified. • Minimum filling ratios giving stable operating conditions have been identified.