Functionalized graphene nanoplatelet-nanofluids for solar thermal collectors

This work reports on the characterization of new heat transfer fluids consisting in dispersions of functionalized graphene nanoplatelets (fGnP) in Havoline XLC Premixed 50/50 base fluid. Optical, stability and rheological properties have been considered, with the aim to assess the nano-suspension potential for volumetric direct solar absorbers. Nanoparticle addition leads to a considerably higher sunlight absorption with respect to the pure base fluid even at the investigated extremely low concentrations (0.005% and 0.05% wt). Rheology tests show a Newtonian behaviour in the shear rate range between 10 and 1000 s−1. Viscosity and thermal conductivities do not significantly increase with respect to the pure base fluid, showing that these new fluids will not require additional pumping powers to flow. •Nanofluids consisting of functionalized graphene nanoplatelets in Havoline XLC have been prepared and characterized.•A considerable sunlight extinction is obtained in short path lengths, even at low nanoparticle loading.•Obtained dynamic viscosity shows that the fluids are Newtonian in all studied conditions.•No significant viscosity increase with nanoparticle addition was found.•Therefore pumping powers necessary to make these new fluids flow will not noticeably rise.