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High Frequency Low Amplitude Temperature Oscillations in Loop Heat Pipe OperationThe operating temperature of a loop heat pipe (LHP) with a single evaporator is governed by the compensation chamber (CC) temperature, which in turn is a finction of the evaporator power, condenser sink temperature, and ambient temperature. As the operating condition changes, the CC temperature will change during the transient but eventually reach a new steady temperature. Under certain conditions, however, the LHP never really reaches a true steady state, but instead displays an oscillatory behavior. This paper presents a study on the oscillation of the loop operating temperature with amplitudes on the order of one degree Kelvin and frequencies on the order of 10(exp -1) to 10(exp -2) Hertz. The source of the high frequency temperature oscillation is the fast movement of the vapor front in the condenser section, which usually occurs when the vapor front is near the condenser inlet or the condenser outlet. At these locations, the vapor front is unable to find a stable position for the given operating conditions, and will move back and forth. The movement of the vapor front causes the movement of the liquid in the condenser and the liquid line, leading to oscillations of the CC and the loop temperatures. Factors that affect the vapor front movement include evaporator power, condenser sink temperature, body forces and whether or the CC temperature is actively controlled. As long as there are no large thermal masses attached to the evaporator, the loop can self adjust rather quickly and the vapor front will move rapidly around the condenser inlet or outlet, leading to high frequency temperature oscillations. The amplitude of temperature oscillation is usually the largest in the liquid line, up to 20 degrees Kelvin in many cases, but diminishes to less than one degree Kelvin in the CC. Furthermore, the high frequency temperature oscillation can occur at any CC temperature when the right combination of the evaporator power and condenser sink temperature prevails.
Document ID
20030020784
Acquisition Source
Goddard Space Flight Center
Document Type
Preprint (Draft being sent to journal)
Authors
Ku, Jentung
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 21, 2013
Publication Date
January 1, 2003
Subject Category
Mechanical Engineering
Meeting Information
Meeting: 33rd ICES Conference
Location: Vancouver
Country: Canada
Start Date: July 7, 2003
End Date: July 10, 2003
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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