Experimental investigation of laminar forced convective heat transfer of Graphene–water nanofluid inside a circular tube

In this paper, convective heat transfer coefficient of Graphene–water nanofluid in a laminar flow through a circular pipe with uniform wall heat flux is investigated experimentally. To achieve this aim, the nanofluid is synthesized chemically in various concentrations, and a testbed is constructed. The effective thermal conductivity and viscosity of the Graphene–water nanofluids are measured via hot wire method and an Ubbelohde viscometer, respectively. Results show that addition of low amounts (up to 0.02% volume fraction) of Graphene nanoparticles to water considerably increases the thermal conductivity and the convective heat transfer coefficient of the working fluid. Maximum enhancements are observed at 0.02% concentration. These enhancements are 10.3% for thermal conductivity and 14.2% for heat transfer coefficient at Re = 1850. Moreover, the stability of the prepared nanofluids is examined by using the UV–vis spectroscopy and is proved to be acceptably high. Finally, the results of the taken AFM images implied no agglomeration of nanoparticles.