Thermal performance of a helium pulsating heat pipe.

A Pulsating Heat Pipe (PHP) utilizing helium as the working fluid and operating between 3 K and 5.2 K under a variety of conditions demonstrates effective thermal conductivity values as high at 60,000 W/m-K. Heat rates up to 0.9 watts are transferred from the evaporator end and absorbed at the condenser end by a Sumitomo RDK-408A2 cryocooler. The PHP is comprised of stainless steel tubing with inner and outer diameters of 0.5 mm and 0.8 mm respectively and looping back and forth between the evaporator and condenser ends 21 times. The condenser, adiabatic and evaporator sections have respective lengths of 0.1 m, 0.3 m and 0.1 m. Here we report data from an on-going experiment that describes the performance of the PHP under random changes and distributions of heat load on the evaporator. The completely passive yet significant heat transfer characteristics of the PHP enable localized cooling such as provided at the cold tip of a cryocooler to be effectively spread over a broad region with minimal added mass and without the need for any auxiliary mechanical pumping. The triple point and critical point temperature of the working fluid usually determine the operating temperature range of the PHP. In the case of helium, the lower temperature limit of the PHP is determined by the thermal balance between the cooling power of the cryocooler and the heat load to the PHP. Significantly lower temperatures are possible with systems that incorporate more stringent thermal isolation.