Heat transfer characteristics of single circular jet impinging on a flat surface with a protrusion

An experimental investigation of heat transfer from a single circular jet impinging normally on a flat plate with a protrusion of depth 1, 2 and 3 mm was carried out. The temperature was measured over a Reynolds number range of 10,000 to 33,000 and nozzle exit-to-plate spacing ranged from 2 to 10 jet diameters. The average heat transfer characteristics were compared with the results from the literature, and the agreements were good. Further, numerical simulations were performed using ANSYS Fluent 18.1 to compare the results with those from experiments. The results showed that the increase of jet Reynolds number and relative depth of protrusion enhances the heat transfer on the impinging surfaces up to 16.69% compared to a flat surface. The maximum increase in the Nusselt number occurs at a spacing of 5 jet diameters (nearly at the end of Potential core zone) and Reynolds number 33000 for all cases. Further, the average percentage change of Nusselt number over the Reynolds number range decreased from 9.74% to 4.73% as protrusion depth increases from 0 to 3 mm due to flow separation. The study of the effect of heat input on the heat transfer enhancement was carried out by comparing Nusselt number for heat supply values of 60 W and 90 W. For higher heat input (90 W) and longer stand-off distance (Z/d = 10) it was observed that the effects of weak impingement flow field are counter acted by natural convection plume flow emanating from the heated surface. Hence, in such cases, impingement cooling is not effective.