Mixed convection of alumina–water nanofluid inside a vertical annulus was investigated.
Modified two-component heterogeneous model for the nanofluid was used.
Asymmetric heating at the walls changes the direction of nanoparticle migration.
The efficacy of using nanofluids is always reduced for heat flux ratio ɛ > 1.
Using smaller nanoparticles enhances the efficacy of using nanofluids.