Abstract:
This paper investigates the thermophysical properties and heat transfer performance of
graphene nanoplatelet (GNP) and alumina hybrid nanofluids at different mixing ratios. The
electrical conductivity and viscosity of the nanofluids were obtained at temperatures
between 15–55°C. The thermal conductivity was measured at temperatures between
20–40°C. The natural convection properties, including Nusselt number, Rayleigh number,
and heat transfer coefficient, were experimentally obtained at different temperature
gradients (20, 25, 30, and 35°C) in a rectangular cavity. The Mouromtseff number was
used to theoretically estimate all the nanofluids’ forced convective performance at
temperatures between 20–40°C. The results indicated that the thermal conductivity
and viscosity of water are increased with the hybrid nanomaterial. On the other hand,
the viscosity and thermal conductivity of the hybrid nanofluids are lesser than that of mono-
GNP nanofluids. Notwithstanding, of all the hybrid nanofluids, GNP-alumina hybrid
nanofluid with a mixing ratio of 50:50 and 75:25 were found to have the highest
thermal conductivity and viscosity, enhancing thermal conductivity by 4.23% and
increasing viscosity by 15.79%, compared to water. Further, the addition of the hybrid
nanomaterials improved the natural convective performance of water while it deteriorates
with mono-GNP. The maximum augmentation of 6.44 and 10.48% were obtained for
Nuaverage and haverage of GNP-Alumina (50:50) hybrid nanofluid compared to water,
respectively. This study shows that hybrid nanofluids are more effective for heat
transfer than water and mono-GNP nanofluid.
