Regulatable thermal conductivity and excellent mass transport of water-filled carbon nanotube as capillary wicks

Passive liquid cooling of ultrathin heat pipe has received considerable attention due to its excellent per-formance of removing heat from hot spot of electronic devices. However, achieving controllable thermal conductivity of the capillary wick materials to reduce the start-up time and total thermal resistance re-mains a challenge. Here we propose the capillary wick of carbon nanotube array to regulate its heat trans-fer performance via the water filling ratio. Molecular dynamics simulation results found that the thermal conductivity of water-filled carbon nanotubes is reduced by 17.8%-23.8%, which is benefit to start-up op-eration. At overheating operation, the high thermal conductivity of empty carbon nanotube can reduce the temperature of the endothermic surface. Importantly, the thermophoretic movement speed of water can reach up to 74 m/s and radial mass exchange occurs driven by temperature gradient. Phonon spectral analysis and heat flow decomposition revealed that the decrease of water-filled carbon nanotube thermal conductivity originates from the low-energy coupling of van der Waals force between water molecules and carbon nanotube and the thermal motion of two water molecules layers. The regulatable thermal conductivity and excellent mass transport performance demonstrate the promising potential of carbon nanotube as next-generation capillary wick of ultrathin heat pipe.(c) 2022 Published by Elsevier Ltd.

Automated summary

This study proposes a capillary wick material based on carbon nanotube arrays, which can regulate its heat transfer performance by controlling the water filling ratio. Molecular dynamics simulation results show that the thermal conductivity of water-filled carbon nanotubes is reduced, which is beneficial for start-up operation. In addition, empty carbon nanotubes have high thermal conductivity and can reduce the temperature of the endothermic surface.