(135a) Application of Novel Porous Graphene Nanoplatelets Composites for Enhanced Heat Transfer Properties

Pool boiling or two phase heat transfer techniques dissipate a large amount of heat by maintaining low surface temperatures as compared to single-liquid phase based heat transfer processes. The maximum amount of heat that can be dissipated from the surface is determined by critical heat flux (CHF), while the efficiency of the boiling is determined by heat transfer coefficient (HTC). Pool boiling finds applications where the devices generate a large amount of heat, such as high-power density electronic devices, nuclear reactors, reboilers, and heat exchangers. The pool boiling performance can further be improved by surface enhancement techniques such as micro/nano porous coatings and by implementing high thermal conductivity materials. In the recent years several carbon-based nanomaterials have been exploited for pool boiling applications due to their high thermal properties and surface areas

We investigated carbon nanotubes, multilayered chemical vapor deposited graphene/graphene oxide, and graphene nanoplatelets (GNP) coatings and achieved higher pool boiling performance with graphene nanoplatelets (GNP), however, the GNP coatings did not sustain the repetitive pool boiling tests making them ineffective for industrial applications. To overcome this, we developed novel copper-GNP (Cu-GNP) porous coatings by a multistep electrodeposition technique owing to higher thermal properties of copper particles.

Hierarchal porous surfaces with diverse morphologies were obtained by varying the electrodeposition process parameters and the concentration of GNP in the composites which were confirmed by scanning electron microscope (SEM). The rendered surfaces were hydrophilic in nature possessing higher wickability. The durability of the coatings was confirmed using the repetitive pool boiling studies. The composite coating with 2% GNP (weight/volume) produced a very high CHF of 286 W/cm² and HTC of 204 kW/m²-°C, representing an improvement of 130% in CHF and 290% in HTC compared to pristine copper surface. The proposed mechanism of enhanced heat transfer properties is attributed to the surface pores that serve as nucleation sites for additional bubble formation that depart in upward direction creating a turbulent convection that further improves the heat transfer rate.