Nonhomogenous modeling of nanofluidic energy transport accounting for thermophoretic migration of nanoparticles inside laminar pipe flows

In this paper, heat transfer in a laminar convective flow of nano-fluids through a circular duct is investigated, and the results are presented. The study has been conducted under uniform heating and cooling conditions. A numerical analysis for water-alumina (AI₂O₃) nanofluids has clearly shown that the conventional homogeneous properties of nanofluids cannot explain the enhancement of the Nusselt number observed in experiments. A nonhomogeneous nano-fluid model using Brow- nian diffusion and thermophoresis effects has been incorporated in the present numerical analysis. Results indicate that the Darcy friction factor decreases under heating and increases under cooling condition than predicted by a pure-fluid correlation. The Nusselt number shows an increasing trend with increasing nanoparticle volume fraction for heating, but the values are lower than predicted by using a pure-fluid correlation for cooling. Results also indicate that nanofluids might act as good coolants under heating condition, but not under cooling condition.