Experimental and numerical investigations of slot jet impingement with and without a semi-circular bottom confinement

•A bottom semi-circular confinement enhances heat transfer from cylinder for lower nozzle to cylinder distance.•For the thinner air jet, confinement effect is negligible.•Maximum enhancement in heat transfer depends on flow and geometric parameters. In this paper, the details of experimental and numerical investigations of slot air jet impingement cooling of a circular heated cylinder have been presented. To improve heat transfer rate behind the cylinder, a semi-circular confinement is also considered. In the parametric study, the Reynolds number ReD, defined based on the cylinder diameter D, is varied from 6000 to 20,000. The ratio of the spacing between the nozzle exit and the heated cylinder H to the width S of the nozzle, H/S is varied from 2 to 12 and the non-dimensional parameter, the diameter of the target to the slot width, D/S=5.5, 8.5 and 17 are considered. To understand the effect of the bottom flow confinement, the ratio of the confinement radius Rc to the radius R, of the heated cylinder, Rc/R was varied from 1.7 to 3.7 and the ratio of the width of the bottom opening W of the confinement to the radius of the heated cylinder, W/R is varied from 0 to 1.2. Numerical simulations are carried out using the v′2‾-f model to obtain the flow pattern and temperature distribution over the cylinder and in the fluid region. In the case of jet impingement flow with a semi-circular confinement wall behind the target cylinder, after the flow separation from the cylinder, the heated fluid is diverted towards the inner wall of the confinement. The major part of the diverted hot fluid leaves through the opening provided at the bottom of the flow confinement without a direct contact with the bottom surface of the heated cylinder. In the case of smaller size semi-circular confinement walls, Rc/R=1.7 and 2.6, the strength of recirculation is higher than that of the unconfined flow and the flow with a larger size confinement. Hence, the local Nusselt number values are higher at the bottom surface of the heated cylinder when smaller size semi-circular confinement walls are used behind the cylinder.