Boiling Performance of Graphene Oxide Coated Copper Surfaces at High Pressures

Graphene has been investigated due to its mechanical, optical, and electrical properties. Graphene's effect on the heat transfer coefficient (HTC) and critical heat flux (CHF) in boiling applications has also been studied because of its unique structure and properties. Methods for coating graphene oxide (GO) now include spin, spray, and dip coating. In this work, graphene oxide coatings are spray coated on to a copper surface to investigate the effect of pressure on pool boiling performance. For example, at a heat flux of 30 W/cm², the HTC increase of the GO-coated surface was 126.8% at atmospheric pressure and 51.5% at 45 psig (308 kPa). For both surfaces, the HTC increases with increasing pressure. However, the rate of increase is not the same for both surfaces. Observations of bubble departure showed that bubbles departing from the graphene oxide surface were significantly smaller than that of the copper surface even though the contact angle was similar. The change in bubble departure diameter is due to pinning from micro- and nanostructures in the graphene oxide coating or nonhomogeneous wettability. Condensation experiments at 40% relative humidity on both the plain copper surface and the graphene oxide coated surface show that water droplets forming on both surfaces are significantly different in size and shape despite the similar contact angle of the two surfaces.