Heat transfer and energy performance of Al2O3/water nanofluid in a 90° bend with circular cross-section are investigated in the range of Reynolds number(Re)from 5 000 to 30 000,particle volume concentration(Φ)from 0.005％to 4％,Schmidt number(Sc)from 9 870 to 296 100,Dean number(De)from 6 636 to 14 847.The momentum and energy equations of nanofluid together with the dynamic equation for nanoparticles are solved numerically with the particle convection,diffusion,coagulation and breakage taken into consideration.Some results are validated by comparing with the available experimental or numerical results.The effect of Re,Φ,Sc and De on the friction factor and heat transfer of Al2O3/water nanofluidis discussed.The results showed that the particle number decreases along the pipeline.Increasing De,Sc leads to a decrease and increase of Φ,respectively.The mean particle diameter and particle polydispersity increase with increasing Debut with decreasing Sc.The friction factor increases with increasing Φ,Sc De and Pr but with decreasing Sc.The ratio of energy performance evaluation criterion(PEC)for the Al2O3/water nanofluid to the base fluid increases with increasing Re,Φ and De,but with decreasing Sc.Finally,the expression of ratio of energy PEC for the nanofluid to the base fluid as a function of Re,Φ,Sc and De is derived.