Power-conversion systems for space power use a thermodynamic cycle to convert thermal energy from a heat source to electrical power. Radiators containing heat pipes are used to reject the waste heat from the thermodynamic cycle into space. The heat pipes serve two purposes. First, they transport and spread heat from the power-conversion system coolant loop into the radiator’s large radiating surface. Second, they improve system reliability by decreasing the effect of micrometeoroid strikes on radiator performance in comparison to radiators using a fluid loop throughout the panel. The following photograph shows an example of such a panel. This small subscale panel was produced as a demonstration unit for NASA’s Prometheus program and is currently undergoing thermal performance tests at the NASA Glenn Research Center. Full-size panels could be many square meters in size and utilize hundreds of heat pipes, depending on the size of the power-conversion system.
Radiator demonstration unit panel.
Although heat pipes using a copper envelope and water for the working fluid are commonly used for cooling low-temperature consumer electronics, large space-power-conversion systems require heat pipes capable of operating at much higher temperatures, between 350 and 500 K, for example. There had been little development of heat pipes in this temperature range. To determine the manufacturing capability and to gather operational data for heat pipes in this temperature range (often referred to as “intermediate temperature heat pipes”), Glenn tasked three heat pipe vendors to design, build, and deliver three heat pipes each of a design prototypic for a space-power-conversion system. Each vendor used heat pipe wicks of their own design. The heat pipes delivered to NASA use water as their working fluid and are constructed of commercially pure CP2 titanium tube, 1.27 cm in diameter by approximately 120 cm long.
The nine heat pipes are presently undergoing performance and life testing in Glenn’s heat pipe laboratory as shown in the following photograph. Power is supplied to the heat pipe through an electrically heated aluminum block clamped to the heat pipe’s evaporator section. Heat is removed from the heat pipe condenser section through a gas gap calorimeter cooled by a commercial chiller. Heat pipe performance is measured via thermocouples attached along its length as well as heater and calorimeter instrumentation. Data logging and experiment control is accomplished using a computer running LabVIEW software (National Instruments Corporation).
Glenn’s heat pipe laboratory.
The tests will provide performance data for use in radiator and power-conversion system analytic models, will verify predicted performance capability at temperatures from 350 to 500 K, and will use life tests to assess the ability of the heat pipes to perform reliably in a multiyear mission without significant performance degradation. Tests to date indicate that, depending upon the wick configuration, the heat pipes transport between 250 and 500 W while operating at 500 K.
Find out more about the research of Glenn’s Thermal Energy Conversion Branch: http://www.grc.nasa.gov/WWW/TECB/
Glenn contacts:
Duane E. Beach, 216-433-6285, Duane.E.Beach@nasa.gov
Lee S. Mason, 216-977-7106, Lee.S.Mason@nasa.gov
Author:
Duane E. Beach
Headquarters program office:
Exploration Systems Mission Directorate
Programs/projects:
Prometheus/Fission Surface Power
Last updated: December 14, 2007
Responsible NASA Official:
Gynelle.C.Steele@nasa.gov
216-433-8258
Point of contact for NASA Glenn's Research & Technology reports:
Cynthia.L.Dreibelbis@nasa.gov
216-433-2912
SGT, Inc.
Web page curator:
Nancy.L.Obryan@nasa.gov
216-433-5793
Wyle Information Systems, LLC
