Thermal performance of a meter-scale horizontal nitrogen Pulsating Heat Pipe

Cooling dry superconducting magnets using cryocoolers as a cold source is becoming a standard. Due to their simple operation, compact configuration, lightness, and thermal performance, Pulsating Heat Pipes (PHP) are good candidates, as two-phase thermal links, for these kind of systems. Initially developed to cool small electronic devices at ambient temperature, PHP have been also studied, in the cryogenic field, using N-2, He, Ne and H-2 as working fluids. In this paper, we present the thermal performances of a 1m long horizontal PHP made of 36 stainless steel parallel tubes. The tube internal diameter is 1.5mm, close to the critical diameter (similar to 1.7 mm) to maintain capillary forces necessary to the PHP operation. Both, the evaporator and condenser sections are copper made and are separated by an adiabatic section. This PHP has been studied using N-2 as working fluid with the condenser temperature maintained at 75 K. Several pressure and temperature sensors placed in the three different sections allow monitoring the thermodynamic behavior of the PHP. Tests have been performed increasing and varying the input power as well as keeping it constant during long periods of time. The maximum equivalent thermal conductivity measured is 85 kW/m.K. This system can transfer a maximum heat power of 25 W before reaching its operation limit.