Numerical simulations of laminar convective heat transfer with nanofluids in two different geometries involving a straight pipe and a 90o curved pipe are presented. The Navier- Stokes and energy equations for an incompressible Newtonian fluid are solved in a body fitted coordinate system using a control-volume method. In the present work, the nanofluid is a mixture of water and alumina particles, and its thermophysical properties are considered as a function of temperature as well as particle concentration. The accuracy of the models employed for estimating the effective thermophysical properties of this nanofluid are first evaluated using available experimental data for heat transfer in a straight pipe. The same models are then employed for the simulation of flows in a curved pipe. Present results indicate that both the nanoparticle and curvature effects enhance the heat transfer performance but at the expense of increased pressure drop. However, in the present case, the nanoparticle contribution to the pressure drop is dominant, which increases by up to two orders of magnitude at higher nanoparticle concentrations. The ratio of the nanofluid Prandtl number to the based fluid Prandtl number is established as a criterion for the choice of a nanofluid. This ratio must be less than 1 to achieve higher heat transfer rates with relatively low pressure drops as the particle concentration is increased.

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