Graphene Nanofluids as Thermal Management Materials: Molecular Dynamics Study on Orientation and Temperature Effects

The dispersion of graphene nanoparticles in a fluid can enhance the thermophysical properties of the base liquid. The physics behind such a phenomenon has yet to be uncovered in the community. In this work, thermal transport in a graphene–water mixture is studied by classical molecular dynamics simulations. Several factors including orientation angle, curvature, thermal rectification, temperature, and van der Waals interaction are investigated, and special attention is paid to the effect on thermal conductance across graphene–water interfaces. It is found that thermal conductance increases from 13.92 to 26.70 MW/m2 K as the orientation angle is increased from 0° to 90°. When the curved graphene is introduced by altering the length to width ratio from 1.0 to 1.8, the thermal conductance is elevated. However, as the length to width ratio exceeds 1.8, such a trend does not continue due to the variation of the intrinsic thermal conductivity of graphene and the formation of the complex graphene–water interface. Even though the curved graphene introduces an asymmetric assembly, no thermal rectification effect is observed for diverse directions of heat flux. It is demonstrated that the enhancement of overall thermal conductance of nanofluids is ascribed to the interface thermal transport rather than the base liquid with increasing temperature. This correlation is suppressed in a hydrophilic interface due to the structural change of liquid layer adjacent to the interface.