Modeling of convective turbulent heat transfer of water-based Al2O3 nanofluids in an uniformly heated pipe

Turbulent convective heat transfers of Al2O3-water nanofluid flowing in a circular tube subjected to an uniform wall heat flux are numerically investigated using different turbulence models. Four nanoparticle volume concentrations φ up to 2% are considered for bulk Reynolds numbers within the range 3000⩽Re⩽20,000. The effects of the nanoparticle concentration and the Reynolds number on the Nusselt number and friction factor are reported. Two different numerical approaches including the single-phase and the mixture two-phase models with variable thermophysical properties are favorably compared to experimental results obtained from the literature for low nanoparticle concentrations (φ⩽0.5%). The results at a higher volume fraction φ=2% show the necessity to use a mixture model. Eight turbulence models in their low-Reynolds number formulation are also compared to assess their ability to predict the effect of turbulence on the convective heat transfer. The SST k-ω model was found to perform the best with errors in terms of the average Nusselt number and friction coefficient of 0.44% and 1.82% respectively. On the contrary, the linear pressure-strain Reynolds Stress Model completely failed to provide the good values with discrepancies of 41.91% and 133.54%, respectively. Finally, the benefit of using this nanofluid is discussed regarding four merit criteria.