Numerical investigation of confined single jet impinging on a dimpled target surface using Al₂O₃-water nanofluids

Jet impingement has been investigated widely owing to its high rates of convective heat transfer near the stagnation zone. Nanofluids, beyond the traditional working fluids, have great advantages in high-rate-heat flux removal. In the present work, a confined single jet impinging on a dimpled target surface with Al₂O₃-water nanofluids as a working fluid was investigated numerically for the first time. The effects of the jet Reynolds number Rej (10,000-20,000) and nanoparticle volume concentration φ (0-5%) on the flow structures and heat transfer characteristics were investigated. The geometrical parameters were H/Dj = 6, Dj/D = 0.5, and δ/D = 0.2. The vorticity contours and streamlines of the confined domain, wall shear stress and pressure coefficient on the target surface, the pumping power, and the Nusselt number distributions were obtained. The results indicated that the effects of Rej and φ on the flow field and heat transfer performance were magnified due to the interaction between them. A flow separation emerged near the dimple edge and got smaller with increase in Rej. The changes of three high vorticity magnitude zones in the confined domain depended on the variation of Rej and φ. The regularity of change in the Nusselt number was complex and the physical properties of the working substance had great effect on it. Furthermore, the concept map of the flow structures of nanofluids in confined impingement and correlations have been derived from the parameter analysis.