A heat pipe can efficiently transfer heat through it liquid-vapor phase change mechanism. Among different heat pipes, loop heat pipe (LHP) and pulsating heat pipe (PHP) are known to be capable of high heat flux/high load heat transfer. In this article, LHP and PHP heat transfer systems are combined to achieve passive, reliable and long-distance heat transfer for successful thermal management of modern avionic systems. Aiming at this development goal, a 2m long LHP is designed to transport heat from the avionics chassis to the remote heat rejection site. To reduce saturation pressure and ensure structural safety at higher operating temperature, water is used as the operating fluid of LHP. Within the avionic chassis, conduction heat transfer is enhanced by sandwiching and solder-bonding a PHP between two PCBs (printed circuit boards). Each PHP/PCB assembly is 20cm long and 12.5cm wide, with electrical heaters mounted to mimic electronic heat dissipation. Heat transfer demonstration of the LHP and PHP combo system is conducted in a lab environment with input power varying from 100 to 400W. For all three PHP/PCB assemblies set in the avionic chassis, the maximum heat source temperature is less than 130°C, even when input power is twice as much as the state of the art. The enhanced heat transfer consumes less power, increases system reliability, and enables avionic system operation in harsher environments.

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