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Carbon fiber reinforced polymer (CFRP) composite material is an attractive structural material in applications where mass is critical. The carbon fiber matrix provides strength comparable to steel with only 25% of the density. The CFRP sheet can often also be made thinner than metal with similar mechanical properties, further increasing the mass savings. However, thermal challenges have arisen with the increased use of composites. In the area of electronics enclosures, traditional metal structures conduct and spread heat over large surfaces, but composites act as insulation. Heat generated by components causes internal temperatures to rise and has detrimental impact on the performance and reliability of the electronics. A method is proposed and tested that utilizes constant conductance heat pipes (CCHPs) that penetrate through the CFRP walls. The CCHPs are capable of transporting significant heat energy through a limited cross-section with a minimal temperature penalty.

Under a program funded by the Air Force Research Laboratory (AFRL), Advanced Cooling Technologies, Inc. (ACT) has developed a series of passive thermal management techniques for cooling avionics. Many avionics packages are often exposed to environment temperatures much higher than the maximum allowable temperatures of the electronics. This condition prevents the rejection of waste heat generated by these electronics to the surrounding environment and results in significant ambient heat gain. As a result, heat must be transported to a remote sink. However, sink selection aboard modern aircraft is limited at best. Often, the only viable sink is aircraft fuel and, depending on mission profile, the fuel temperature can become too high to effectively cool avionics. As a result, the electronic components must operate at higher than intended temperatures during portions of the mission profile, which reduces component lifetime and significantly increases the probability of failure.

In military aircraft, electronics are often subjected to operating environments well beyond their survival temperatures and with limited heat sinks. The current approach is to use a Liquid Cooling System (LCS) with either vehicle fuel or Polyalphaolephin (PAO) to cool electronics. However, advanced military platforms have found this approach limits their operational effectiveness. A thermal management system for electronics cooling in high temperature avionics environments is under development using Loop Heat Pipe (LHP) and heat pipe-based technology. The system reduces thermal energy transport inefficiencies within electronics enclosures, identifies potential sinks to provide continuous heat rejection over the operating envelope of the platform, and provides passive thermal energy transport from the electronics enclosure to selected sinks. The system developed to accomplish these tasks is divided into two subsystems.