Heat Pipe Limits in Reduced Gravity Environments

Fission power provides game-changing solutions for powering advanced NASA missions. Radiators are needed to reject waste heat from Fission Power Systems (FPS). Titanium – water heat pipes are being considered for use in the radiators of a fission power system option for lunar exploration. Embedded in the radiators and deployed on the surface, heat pipes would be oriented vertically and would operate as thermosyphons, a subset of heat pipes that have no wick in their condenser. Their design is determined in part by the flooding limit which is attributed to the interfacial shear force at the boundary between liquid and vapor, and occurs when concurrent vapor flow is so severe that liquid flow is prevented. Flooding is determined by the thickness of the fluid film on the walls and the interaction of fluid flow with concurrent vapor counter flow, both inversely proportional to gravity. The planned test objective of this project is to validate the gravity-dependent flooding limit model for thermosyphons.
This work continued with a suborbital flight test in 2015 under T0073 Radial Core Heat Spreader.

Technical Report NASA/TM—2013-217905: Thermosyphon Flooding in Reduced Gravity Environments Test Results
Technical Report NASA/TM—2013-216536: Thermosyphon Flooding in Reduced Gravity Environments
Paper (2012): Thermosyphon Flooding in Reduced Gravity Environments

To date, empirical data of heat pipe limits in microgravity is nonexistent. This adds significant risk to future heat pipe thermal control systems. HEMD and SMD are current and future customers utilizing nuclear power for space.

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