An Eulerian-Lagrangian model for analyzing the flow of nanofluids in duct was developed and the effects of trap and reflect wall boundary conditions for nanoparticles were studied. The two-way coupled model was used and the discrete nature of particles was accounted for the analysis. The model was then used to simulate the laminar flow of Al2O3-water nanofluids between two parallel plates at constant temperatures. The effects of temperature differences between the fluid and the walls including the thermophoresis force were included in the model. The influence of the particle boundary conditions and solid volume fractions on concentration, nanofluid velocity profile and heat transfer rate were investigated. For a fixed values of Reynolds number (Re=100) and particle diameter (dp=30nm), series of simulations were performed for a range of solid volume fraction 0⩽ϕ⩽0.050⩽ϕ⩽0.05 for both trap and reflect boundary conditions for nanoparticle-wall interactions. It was found that for a reflecting wall, the concentration near the wall increased slightly that could cause a slight diffusion away from the wall. For the trapping wall, there was a sharp concentration gradient near the wall and the particles diffused toward the wall. Also, there was a small increase in the average Nusselt number for the reflecting wall in comparison to the absorbing wall.

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