Loop Heat Pipe Temperature Oscillation Induced by Gravity Assist and Reservoir Heating

Date

2015-07-12

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Publisher

45th International Conference on Environmental Systems

Abstract

The Laser Thermal Control System (LCTS) for the Advanced Topographic Laser Altimeter System (ATLAS) to be installed on NASA’s Ice, Cloud, and land Elevation Satellite (ICESat-2) consists of a constant conductance heat pipe and a loop heat pipe (LHP) with an associated radiator. During the recent thermal vacuum testing of the LTCS where the LHP condenser/radiator was placed in a vertical position above the evaporator and reservoir, it was found that the LHP reservoir control heater power requirement was much higher than the analytical model had predicted. Even with the control heater turned on continuously at its full power, the reservoir could not be maintained at its desired set point temperature. An investigation of the LHP behaviors found that the root cause of the problem was fluid flow and reservoir temperature oscillations, which led to persistent alternate forward and reversed flow along the liquid line and an imbalance between the vapor mass flow rate in the vapor line and liquid mass flow rate in the liquid line. The flow and temperature oscillations were caused by an interaction between gravity and reservoir heating, and were exacerbated by the large thermal mass of the instrument simulator which modulated the net heat load to the evaporator, and the vertical radiator/condenser which induced a variable gravitational pressure head. Furthermore, causes and effects of the contributing factors to flow and temperature oscillations intermingled.

Description

Bellevue, Washington
Jentung Ku, NASA Goddard Space Flight Center, USA
Matthew Garrison, NASA Goddard Space Flight Center, USA
Deepak Patel, NASA Goddard Space Flight Center, USA
Franklin Robinson, NASA Goddard Space Flight Center, USA
Laura Ottenstein, NASA Goddard Space Flight Center, USA
The 45th International Conference on Environmental Systems was held in Bellevue, Washington, USA on 12 July 2015 through 16 July 2015.

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