AbstractIn a scenario characterized by a secondary flow called Dean's vortices, thermal and flow behavior analysis is examined. Forced convection of an Al2O3–water nanofluid through a three‐dimensional (3D) 90° elbow was analyzed numerically using a multiphase mixture model. Turbulence is taken into account by using the shear‐stress transportk–ωmodel. Also, entropy production is presented to obtain the optimized conditions. Simulation parameters consist of different Reynolds numbers (10,000100,000), nanoparticle volume fraction , nanoparticle diameter . The findings reveal that the increase in the and theRealong with a smallerdpdiscourages the appearance of Dean vortices in the flow. The pressure drop increases with the increase in the volume fraction and the decrease in the nanoparticles' diameter. The highestNuMis observed at for . Significant heat transfer rates are observed near the outer wall. The minimum total entropy production is obtained atRe = 100,000 for and .