Two-phase mixture simulation of Al₂O₃/water nanofluid heat transfer in a non-uniform heat addition test section

Highlights: •Two-phase nanofluid simulation have been conducted using CFD mixture model. •Effect of nanoparticle concentration on the heat transfer of coolant. •Addition of nanoparticles causes heat transfer coefficient to be increased. -- Abstract: This paper aims to present results of a numerical investigation on Al₂O₃/Water Nanofluid heat transfer. Two-phase mixture model is used to study effects of Reynolds number and nanoparticle concentrations on nanofluid heat transfer in flow around an annulus test section (which is 1 m long annuli). Non-uniform heat flux is assumed as heat boundary condition on annuli inner wall. Annuli wall and bulk temperature profiles, Local and averaged heat transfer coefficient profiles, local and averaged Nusselt number profiles are presented as functions of nanoparticle volume concentrations and Reynolds numbers. Both laminar and turbulence flow regimes are simulated. In order to validate results, they are compared with experimental data. Maximum error between two-phase mixture model results of wall temperature and experimental data is about 12%. Results indicate that two-phase mixture model can predict heat transfer of nanofluid very well. It is also understood that addition of nanoparticles (low concentration) causes heat transfer coefficient to be increased. Profiles of local heat transfer coefficient and Nusselt number would be smoother for higher nanoparticle concentrations. By increasing the concentration, maximum wall temperature decreases but its location goes higher within the fuel rod. The increase in heat transfer due to addition of nanoparticles is less in turbulence flow rather than laminar flow.