Description: A passive Pulsating Heat Pipe (PHP) system is proposed to distribute cooling over broad areas with low additional system mass. The PHP technology takes advantage of the large latent heat associated with phase change of a working fluid that is confined to small capillaries to carry heat efficiently from evaporator regions to a condenser that is attached to the cold head of the cryocooler. This system will have an advantage over other distributed cooling approaches because it will be modular and can interface with any cooler that provides the required cooling power at the load temperature. The cooler may be a Stirling cooler, Pulse Tube cooler, reverse-Brayton cooler, Joule Thompson cooler, or some hybrid combination of these. Because the fluid flow is driven by fluid phase change caused by a temperature difference between the evaporators and the condenser, the loop is self-regulating. Flow is induced only when there is a thermal load. Also, because surface tension forces are dominant in the small capillaries of the PHP, this technology is suited for use in microgravity.

Benefits: The PHP has many possible applications within NASA. These include distributed cooling systems for zero boil off cryogenic storage tanks, in particular for actively cooled shields that may be used to eliminate the need for internal mixing with spray bars. The PHP could also be used to provide distributed cooling for radiation shields and large optical elements used in infrared space science missions.

There are also Missile Defense Agency applications, such as surveillance systems incorporating LWIR focal planes that require cooling of focal planes and optics to temperatures less than 40K. In addition, there are many commercial applications such as cooling superconducting power lines, superconducting magnets for power generation and energy storage and MRI magnets for medical applications.