Modified surfaces using seamless graphene/carbon nanotubes based nanostructures for enhancing pool boiling heat transfer

Abstract

Nanostructures are one of the promising options when it comes to the overall enhancement of boiling systems. Growing carbon nanotubes (CNT) over the Graphene (Gr) coated copper substrates is believed to be one such approach. This study attempts to deliver an insight into this aspect using Gr/CNTs heterostructures, over the copper substrate, using FC-72 as working fluid. PECVD technique was used to grow both the few layer Graphene (FLG) as well as CNT over the copper substrate. The as fabricated structures were characterised using SEM, TEM, Raman Spectroscopy, AFM and contact angle measurement. Through detailed experimentation, it was observed that the Gr/CNT heterostructures improve both the heat transfer coefficient (155%) and the critical heat flux (40%) of the surface as compared to bare copper surface. Most importantly, the boiling incipience superheat was found to reduce drastically (62%) as compared to bare copper surface, which is favourable for electronics cooling application. Increased nucleation sites, capillary effect, lateral heat transfer through Graphene intermediate layer and improved bubble dynamics caused these enhancements. The improved thermal transport properties of the surface as a result of Graphene based intermediate layer and the surface properties due to CNT produced a synergic effect to improve the boiling performance as a whole.