Hybrid Heat Pipes for High Heat Flux Applications

Hybrid wick CCHPs for high power electronics on spacecraft, and NASA landers and rovers is the immediate NASA application. Conventional grooved aluminum/ammonia CCHPs are heat flux limited and are only suitable for operation in space, or when they can be engineered to operate on a planetary surface in a gravity aided mode. The hybrid wicks developed on this program will remove this design constraint, and expand the design space to include higher heat flux operation and operation against gravity on future missions. Wicks developed on this program will enable the use of 3-D CCHPs for some NASA applications: with a hybrid wick, 3-D pipes can be fabricated and ground tested. Additional applications for the hybrid wick were identified, such as heat collecting and spreading for space based and planetary applications. Heat generating electronics are typically buried within an enclosure: the electronics will be mounted in various configurations on circuit cards and aluminum mounting planes. The goal is to accept and isothermalize the thermal load within the enclosure from the individual electronics components and transfer the energy to a location for heat. Strategically embedding heat pipes with hybrid wicks within these planes relevant to the high power components can increase the effective thermal conductivity by 2 to 4 times. These high conductivity plates are essential in the overall Thermal Management System for NASA electronics enclosures applications.

The maximum allowable evaporator heat flux in a grooved pipe is relatively low, typically 10-15 W/cm^2. As spacecraft electronics increase in power and packing density, this can present a thermal control problem. Sintered wicks have much higher evaporator heat flux limits, typically four times higher than grooved wicks. The main non-NASA application will be for CCHPs that remove waste heat from high power components on commercial and military spacecraft. Several interested commercial customers in this technology development have been identified, for cooling of laser based components to high heat flux components on-board commercial satellites. Due to the intensive requirements on Military systems for electronics, there are also severe high heat flux cooling requirements. A hybrid wick CCHP with high heat flux capabilities would be highly beneficial. There are cost and mass penalties to competing technologies, such as Loop Heat Pipes and thermal spreaders.