A continuum mechanical modeling of fully-developed forced convection of nanofluids in a coaxial cylinder

Nanofluid is a suspension of nanoparticles with high thermal conductivity. Many investigations have been performed to find out the mechanism of enhanced heat transfer in the nanofluids. In the present work, we model the Al2O3/H2O nanofluid employing the pseudo-single-phase continuum model and investigate the fully-developed forced convection in a coaxial cylinder under a fixed pressure drop. It is found that the heat transfer coefficients of both the cold inner wall and hot outer wall increase with respect to the inlet mass fraction of nanoparticles. The enhancement of convective heat transfer coefficient is found to be slightly higher than that of thermal conductivity of nanofluid itself due to the drift of nanoparticles. On the other hand, the Nusselt number of cold inner wall increases but that of hot outer wall decreases as the inlet mass fraction of nanoparticles increases. It is revealed that this peculiar behavior of Nusselt number on the hot outer wall is caused by the drift of nanoparticles from the cold inner wall to the hot outer wall due to the thermophoresis. As the inlet mass fraction of nanoparticles increases under the condition of fixed pressure drop, the mixture viscosity increases and the volumetric flow rate is retarded, since the viscous dissipation must balance the input rate of mechanical energy at the steady state.