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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

TRANSIENT THERMAL MODEL FOR LOOP HEAT PIPES

Robert W. Baldauff
U.S. Naval Research Laboratory Washington, DC 20375 USA

Denis R. Mahony
Praxis Inc., Alexandria, VA 22303, USA

Triem T. Hoang
TTH Research Inc., Clifton, VA 20124, USA

Abstract

Loop Heat Pipes (LHPs) have proven themselves as reliable and robust heat transport devices for spacecraft thermal control systems (TCS). Thus far, the LHPs operating in Geosynchronous Equatorial Orbit (GEO), in which the loop operating conditions remain constant, perform very well as expected. In Low Earth Orbit (LEO), orbital variation of the thermal environment does not allow the LHPs to reach a "steady state" as it does in GEO. Hence, their heat transport requirements are dependent not just on the applied heat load but also on the orbit beta angle, thermal mass attached to the evaporator and the TCS operation-specific conditions. LHP performance is characterized in 1-g for steady-state operation and is a good starting point for selecting an initial design. But in order to demonstrate that the LHP can meet its requirements during all phases of the mission, many or all of which are not steady-state, an integrated transient thermal model of the LHPs and the spacecraft environment becomes necessary. The thermal model must be flexible enough to handle different configurations for doing trade studies and yet accurate enough to predict the performance for both 1-g and 0-g operation. It must also be run-time efficient. To this end, a transient fluid/thermal model of an LHP has been developed. In this paper, the theoretical approach to modeling the LHP will be described and comparisons between the model predictions and test data in 1-g will be presented.

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