Capillary pressure in graphene oxide nanoporous membranes for enhanced heat transport in Loop Heat Pipes for aeronautics

We describe a novel application of graphene-based materials to enhance heat transport in sintered metal wicks, which are the core components for Loop Heat Pipe (LHP) evaporators. Standard metal wicks limit the applicability of LHP to about 8-10 m of transport length and around few meters of gravitational head. This is due to the typical average pore size (about 1 mu m) in the sintered metal wicks made of nickel or titanium, which are the most commonly used materials. The idea of the present work is to bond a layer of graphene on top of the wick facing the vapor side of the LHP evaporator. The much smaller pore sizes of graphene (around tens of nanometers) would produce a significant increase in capillary force, while at the same time minimising the pressure drop due to its microscopic thickness (few microns). The wicking height (i.e., capillary rise of a liquid inside a pore) measurements demonstrate that there is an improvement of at least more than 3.5 times when the graphene coating is used, compared to the standard nickel sintered powder wick. This means that the heat transfer of a graphene LHP could work in a spatial range in excess of 28-35 m, which would allow breakthrough applications such as anti-icing of aircraft wings and propellers, as well as wind turbines that cannot be addressed by standard LHP technology. (C) 2016 Published by Elsevier Inc.