Numerical investigation of the effect of oscillating injection nanofluid flow on forced convection heat transfer enhancement over a backward-facing step

In this study, the effect of the oscillating injection flow on laminar forced convection of nanofluid flow over a 2D backward-facing step was numerically investigated. The effects of Reynolds number, Strouhal number, and momentum flux ratio in terms of injection velocity, and injection position on the fluid flow and heat transfer were studied. The comparison of the results of the oscillating injection with different cases (with and without constant injection) indicates that using oscillating injection flow generates periodic oscillation in the flow and heat transfer characteristics, which can lead to heat transfer enhancement. Furthermore, the time-spatial average Nusselt number based on the Strouhal number exhibited a resonant-type behavior, and the best effect of flow oscillation on the heat transfer rate was achieved at St = 0.1. The numerical results showed that the oscillating injection can provide a heat transfer enhancement of about 144% in X-j = H for Reynolds number of (Re = 100) and momentum flux ratio of (J = 4). Moreover, it was found that the maximum effectiveness parameter, as a sufficient and reliable criterion, at the Re = 100 is equal to eta=1.54.