Performance enhancement of graphene-coated micro heat pipes for light- emitting diode cooling

JS Gan and H Yu and MK Tan and AK Soh and HA Wu and YM Hung, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 154, 119687 (2020).

DOI: 10.1016/j.ijheatmasstransfer.2020.119687

The rate of water transport through graphene nanocapillaries is profoundly enhanced compared to that in microscale capillaries due to the prevalence of exceptionally high capillary pressures and large slip lengths. As an inaugural study, we integrate graphene nanocapillaries into a micro heat pipe (MHP) for enhanced light-emitting diode (LED) cooling. With the use of graphene nanocapillaries, the ultrafast water transport synergically enhances the water circulation and evaporation process in the microfluidic device. The graphene-coated MHP achieves more than 45% enhancement in the overall performance compared to the uncoated counterpart. In turn, the experiments demonstrate a drastic reduction of LED's operating temperature (more than 25 degrees C) which translates into a significantly prolonged lifespan of LED. The molecular dynamics simulations reveal that the oxygenated functional groups attached on graphene further increase the capillary pressure (similar to 1000 bar) and effective velocity (similar to 20 m/s) of the nanoconfined water, compared to those (similar to 500 bar and similar to 10 m/s) in a pristine graphene nanochannel. The ultrafast water transport in graphene nanocapillary is justified. This study provides a holistic analysis and important insight into the phenomenon of ultrafast water transport in graphene nanocapillaries that exhibits an enormous potential in thermal energy management applications for LED cooling. (C) 2020 Elsevier Ltd. All rights reserved.

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