A two-condenser pulsating heat pipe for use as a passive thermal disconnect in redundant cryocooler implementations

A proof-of-concept, two-condenser nitrogen pulsating heat pipe (PHP) for use as a passive thermal switch in applications with redundant cryocooler installations is developed and tested. The PHP design comprises two independent PHP condensers, each thermally linked to an independent cryocooler cold head, with the two associated PHP evaporators attached to a common cold plate heat load. The design allows the cold plate heat load to be continuously cooled when one cryocooler is non-operating. This is accomplished by leveraging the thermal isolation provided by dryout in the PHP associated with the non-operating cryocooler to limit the parasitic load on the common cold plate (and therefore on the remaining operating cryocooler) from the ambient environment. Mechanical actuation is not required as the PHP thermal switch is fully passive. Instrumentation is included in the proof-of-concept device to measure the heat loads and effective thermal conductivities of each PHP. The design of the system is presented in detail, along with preliminary measurements of PHP heat loads and PHP effective thermal conductivities in states of both pulsating advection and dryout.