Functionalized few-layered graphene nanoplatelets for superior thermal management in heat transfer nanofluids

Abstract

The superior thermal conductivity and lightweight of graphene flakes make them materials of choice for advanced heat transfer applications, especially for transport of electricity from sustainable power stations such as concentrating solar power plants. In view of the excellent thermal conductivity of graphene or graphene-like nanomaterials (3000–5000 W m−1 K−1), their dispersion into conventional host fluids such as water (0.613 W m−1 K−1) or ethylene glycol (0.25 W m−1 K−1) can significantly improve fluid heat transfer characteristics. The two-dimensional structure and high surface area as well as the cost-efficient carbon-based material make graphene nanoplatelets (GNPs) suitable for large-scale applications in colloidal thermal conductive fluids. For an efficient dispersion of GNPs in base fluids, intrinsically hydrophobic GNPs were acid treated to obtain highly concentrated (4 wt.%) graphene-based nanofluids. Investigations on various GNP sizes and reaction parameters showed significant influences on the resulting thermal conductivity values of the nanofluid. After 14 h measurements in a dormant system, the most efficient nanofluid reached a thermal conductivity of 0.586 W m−1 K−1 (the base fluid of 0.391 W m−1 K−1) and a low viscosity of 6.39 cP resulting in an overall efficiency improvement of 77%, when compared to the base fluid without particles.