Experiment on forced convective heat transfer enhancement using MWCNTs/GNPs hybrid nanofluid and mini-tube

The development of new classes of fluids with enhanced heat transfer capabilities has been the subject of significant contemporary research. One area of interest in this field involves the use of nanomaterials to improve the properties of heat-transfer fluids. This research experimentally investigates promising hybrid nanofluids that contain graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs). The present article reports thermophysical properties, heat transfer coefficient, and pressure drop for MWCNTs/GNPs water based hybrid nanofluids that flow through a circular tube (Din = 1.1 mm). The flow was assumed as a fully laminar flow (Re = 200-500), and a uniform heat flux was applied to the tube surface. Different weight concentrations of MWCNTs/water nanofluids (0.075, 0.125, and 0.25 wt%) were used and mixed with (0.035 wt%) GNPs to prepare hybrid nanofluids. Heat transfer coefficient was significantly enhanced using MWCNTs and MWCNTs/GNPs hybrid nanofluids. The enhancement of heat transfer coefficient is found to be proportionally dependent on the nanoparticle concentrations and inversely related with the Reynolds number. The positive effect of adding GNPs to different concentrations of MWCNTs enhanced the heat transfer coefficient. The maximum enhancement was recorded for 0.25 MWCNTs/0.035 GNPs hybrid at Re = 200 for a 43.4% increase with an 11% rise in pressure drop.