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Optimized Heat Pipe Backup Cooling System Tested with a Stirling ConvertorIn a Stirling Radioisotope Power System (RPS), heat must be continuously removed from the General Purpose Heat Source (GPHS) modules to maintain the modules and surrounding insulation at acceptable temperatures. The Stirling convertor normally provides this cooling. If the Stirling convertor stops in the current system, the insulation is designed to spoil, preventing damage to the GPHS at the cost of an early termination of the mission. An alkali-metal variable conductance heat pipe (VCHP) can be used to passively allow multiple stops and restarts of the Stirling convertor by bypassing the heat during stops. In a previous NASA Small Business Innovation Research (SBIR) Program, Advanced Cooling Technologies, Inc. (ACT) developed a series of sodium VCHPs as backup cooling systems for the Stirling RPS. In 2012, one of these VCHPs was successfully tested at NASA Glenn Research Center with a Stirling convertor as an Advanced Stirling Radioisotope Generator (ASRG) backup cooling system. The prototype; however, was not optimized and did not reflect the final heat rejection path. ACT through further funding has developed a semioptimized prototype with the finalized heat path for testing at Glenn with a Stirling convertor. The semioptimized system features a two-phase radiator and is significantly smaller and lighter than the prior prototype to reflect a higher level of flight readiness. The VCHP is designed to activate and remove heat from the GPHS during stoppage with a small temperature increase from the nominal vapor temperature. This small temperature increase from nominal is low enough to avoid risking standard ASRG operation and spoiling of the multilayer insulation (MLI). The VCHP passively allows the Stirling convertor to be turned off multiple times during a mission with potentially unlimited off durations. Having the ability to turn the Stirling off allows for the Stirling to be reset and reduces vibrations on the platform during sensitive measurements or procedures. This paper presents the design of the VCHP and its test results with a Stirling convertor at Glenn. Tests were carried for multiple on and off cycles to demonstrate repeatability. The impacts associated with the addition of the VCHP to the system are also addressed in terms of mass and additional heat losses due to the presence of the VCHP.
Document ID
20160004351
Acquisition Source
Glenn Research Center
Document Type
Technical Memorandum (TM)
Authors
Schwendeman, Carl L. (Advanced Cooling Technologies, Inc. Lancaster, PA, United States)
Tarau, Calin (Advanced Cooling Technologies, Inc. Lancaster, PA, United States)
Schifer, Nicholas A. (NASA Glenn Research Center Cleveland, OH United States)
Anderson, William G. (Advanced Cooling Technologies, Inc. Lancaster, PA, United States)
Garner, Scott (Advanced Cooling Technologies, Inc. Lancaster, PA, United States)
Date Acquired
April 5, 2016
Publication Date
March 1, 2016
Subject Category
Spacecraft Propulsion And Power
Mechanical Engineering
Report/Patent Number
AIAA Paper 2015-3983
GRC-E-DAA-TN25990
NASA/TM-2016-218912
E-19168
Report Number: AIAA Paper 2015-3983
Report Number: GRC-E-DAA-TN25990
Report Number: NASA/TM-2016-218912
Report Number: E-19168
Meeting Information
Meeting: International Energy Conversion Engineering Conference (IECEC)
Location: Orlando, FL
Country: United States
Start Date: July 27, 2015
End Date: July 31, 2015
Sponsors: American Inst. of Aeronautics and Astronautics
Funding Number(s)
CONTRACT_GRANT: NNC14VC86P
WBS: WBS 138494.04.18.01.01.01
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
Heat Pipe
Cooling
Stirling Engine

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