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Investigation and Optimization of Fluid Charge in Gravity Aided Aluminum-Ammonia Heat Pipes

Author
Smay, Joshua
Published
[University Park, Pennsylvania] : Pennsylvania State University, 2024.
Physical Description
1 electronic document
Additional Creators
Maicke, Brian Allen
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Open Access.
Summary
Aluminum-ammonia constant conductance heat pipes (CCHPs) are one of the most common passive thermal control devices used in the aerospace industry. CCHPs are traditionally filled with enough fluid to fill the axial grooves at a desired saturation temperature in a microgravity environment. However, in ground testing and planetary missions the CCHPs will be affected by gravity, and both the starting transient performance (startup) and steady state performance can be greatly different compared to that in microgravity. The former is largely affected by liquid pooling, or puddling, in the evaporator. The latter can also be affected by potential pooling, as well gravity playing a major role in liquid return. With planetary missions becoming more and more popular, and CCHPs remaining as one of the most trusted aerospace thermal control devices, there exists a need to characterize the effect of gravity on CCHP startup and steady state performance, and investigate if a different fluid charge level may be optimal compared to the traditional filled-groove approach. This study focused on a single CCHP design, and tested multiple power levels and fluid charges to empirically determine the optimal fluid charge in terms of reducing startup transients and optimizing steady state conductance. It was found that this optimal fluid charge was approximately 71% of the traditional filled-groove charge. Furthermore, a simplified finite difference model of the CCHP was developed to predict startup transients for a given CCHP design. This model agreed relatively well with the testing results with an average error of 6% in terms of the temperature difference between evaporator and condenser prior to CCHP startup. This model can be used as a tool to determine if startup transients would hinder a given CCHP design and if charge optimization is needed.
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Dissertation Note
M.S. Pennsylvania State University 2024.
Technical Details
The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
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