Hybrid Heat Pipes for Planetary Surface and High Heat Flux Applications

Novel hybrid wick Constant Conductance Heat Pipes (CCHPs) were developed to solve the high heat flux limitation for future highly integrated electronics. In addition to carrying power over long distances in space, the hybrid CCHP evaporator can also operate against an adverse tilt on the planetary surface for Lunar and Martian landers and rovers. These hybrid heat pipes will be capable of operating at the higher heat flux requirements expected in NASA’s future spacecraft and instruments such as on the next generation of polar rovers and equatorial landers. The thermal transport requirements for future spacecraft missions continue to increase, while at the same time the heat acquisition areas have trended downward, thereby increasing the incident heat flux from 5-10W/cm2 to the projected > 50W/cm2. This exceeds the performance of standard axial groove CCHPs and loop heat pipes (LHPs). Aluminum/ammonia and stainless steel/ammonia hybrid CCHPs to demonstrate high heat flux capability and for planetary (Lunar and Martian) rovers and landers were designed, fabricated and tested. The CCHPs had a sintered powder metal wick in the evaporator and axial grooves in the adiabatic and condenser regions The hybrid wick high heat flux aluminum/ammonia CCHP transported a heat load of 175 watts with heat flux input of 53W/cm2 at 0.1 inch adverse elevation. This demonstrates an improvement in heat flux capability of 3 times over the standard axial groove CCHP design. The hybrid wick high heat flux stainless steel/ammonia CCHP transported a heat load of 165 watts with heat flux input of 51W/cm2 at 0.1 inch adverse elevation. The Thermal Link planetary aluminum/ammonia CCHP transported approximately 202 watts at a 4.2° adverse inclination before dryout, exceeding the 150W target. Also the Thermal Link planetary aluminum/ammonia CCHP was tested for maximum transport power at three different adverse elevations to extrapolate zero-g power. The maximum power at zero-g is 288 watts, exceeding the 150W target. The X-ray micrographs for the interface between the sintered powder metal wick and the axial grooves in the stainless steel hybrid CCHP shows much better contact in comparison to the aluminum CCHP because of the successful internal sintering technique developed during this project.