Graphene has been applied to thermal technology including boiling and condensation heat transfer, from which the pool boiling enhancement relies on adjusting the surface morphology and wettability that is favorable to catalyze the vaporization on the fluid/graphene interface. However, previous works using graphene or reduced graphene oxide (RGO) flake coatings, where the morphology of graphene coating is nonuniform and most of the underlying structured cavities are sealed by graphene flakes. For a long time, this hampered the unraveling of the mechanism behind the enhanced boiling performance by graphene coatings. Moreover, the previous work relied on using water-based pool boiling, which limits the scope of its practical applications since the versatile nonpolar refrigerant has been widely used in boiling heat transfer. The pool boiling was carried out on a plain copper surface to study the effect of fluorinated graphene (F-graphene) coating using nonpolar refrigerant R-141b as the working fluid along with bubble dynamic visualization. It was found that the increase of contact angle leads to more active cavities and enhances heat transfer performance up to twice as much, by applying the F-graphene coating. Moreover, the mechanism of graphene-enhanced heat transfer performance was unraveled and mainly attributed to the hydrophobic surface and effective cavity structure. This research provides a practical and reliable route for enhancing the heat transfer through F-graphene-coatings, which paves the way for potential application in graphene-based thermal technologies.
Keywords: R-141b; fluorinated graphene; graphene; heat transfer; pool boiling; surface modifiers.