Abstract The present paper analyzes the turbulent convection of Al 2 O 3 -water nanofluid inside a circular section tube subjected to constant wall temperature. The analysis is developed numerically by using the mixture model, which has been proved to be a convenient method to simulate nanofluids behavior. The numerical model is successfully validated by means of analytical equations and experimental correlations. The study is focused on the analysis of the performance of Al 2 O 3 -water nanofluid within the considered device. Performance indicators based on the first and second law of thermodynamics are taken into account and analyzed. At the increase of nanofluid concentration, the Nusselt number increases, but entropy generation and pumping power also increase, therefore the penalties overcome the benefits. The results reported in the present paper are believed to be useful for the thermal optimization of nanofluids flow inside tubes.