Loop Heat Pipe for Thermal Management of Aircraft Engine Equipment

Abstract

According to recent aircraft engine development trends, the performance enhancement of the propulsion plants is accompanied by both an increase of the overall pressure ratio and a decrease of the fan pressure ratio. Projections for the next decade show that equipment within the engine compartments can exceed their temperature thresholds, penalizing aircraft safety. Loop heat pipes (LHP) represent a highly appealing solution that could be employed as part of future passive cooling architectures, either replacing or enhancing the heat transfer capabilities of currently adopted monophase solutions. To meet the compatibility, safety, and environmental constraints, a titanium–water LHP was designed, manufactured, and tested for the thermal management of aircraft engine equipment. The results encouraged the use of this technology, providing clues for the development of other prototypes. The sintered titanium wick showed an excellent mechanical resistance to repeated cycles of water freeze/thaw, providing that the LHP could be potentially exposed to a cold environment with limited risk to undergo structural failures. Experimental data suggest that a passivation process occurred in the first hours of operation, modifying wick wettability and improving LHP performance. This was accompanied by the generation of noncondensable gas. The impact on LHP behavior was carefully analyzed, together with the influence of heat transfer on the liquid line and the cold source temperature variations.