In this paper, forced convection flow and heat transfer of a Al2O3/Water nanofluid have been investigated numerically by single and two phase (volume of fluid) models. Nanofluid flows inside the inner tube of the isothermally concentric circular and sinusoidal double tube heat exchangers while hot pure water flows in the outer tube. The single-phase and two-phase models is used to simulate the nanofluid forced convection of 2% and 3% volume concentrations. The renormalization group k-ε model is used to simulate turbulence in ANSYS FLUENT 15.0. Results show that the overall heat transfer coefficient increases with nanoparticle volume concentrations in the heat exchangers. The highest overall heat transfer coefficient rates are detected, for each concentration and shape, corresponding to the highest flow rate for the sinusoidal tube heat exchanger . The maximum overall heat transfer coefficient enhancement is 220% for the particle volume concentration of 3% at the inner tube of concentric sinusoidal double tube heat exchanger corresponding to flow rate =10 LPM. The results reveal that the Al2O3/water pressure drop along the inner tube of circular and sinusoidal double tube heat exchanger increases by about 3% and 5% for volume concentrations of 2% and 3%, respectively, given flow rate compared to the base fluid.Comparison of these results with Rohit S. Khedkar‘s published experimental data, showed good agreement.

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