In this article, the laminar mixed convection of Al2O3-water nanofluid flow in a horizontal flat tube has been numerically simulated. The two-phase mixture model has been employed to solve the nanofluid flow, and constant heat flux has been considered as the wall boundary condition. The effects of different and important parameters such as the Reynolds number, Grashof number, nanoparticles volume fraction, and nanoparticle diameter on the thermal and hydrodynamic performances of nanofluid flow have been analyzed. The results of numerical simulation were compared with similar existing data and good agreement is observed between them. It will be demonstrated that the Nusselt number and the friction factor are different for each of the upper, lower, left, and right walls of the flat tube. The increase of Reynolds and Grashof numbers, nanoparticles volume fraction, and the reduction of nanoparticle diameter lead to the increase of Nusselt number. Similarly, the increase of Reynolds number and nanoparticles volume fraction results in the increase of friction factor. Therefore, the best way to increase the amount of heat transfer in flat tubes using nanofluids is to increase the Grashof number and reduce the nanoparticle diameter.
