Effect of number of round jets on impingement heat transfer from a heated cylinder

•Circumferentially arranged multi-jet impingement improves heat transfer significantly.•At very high curvature ratio, the secondary peak in local Nusselt number is not observed.•Number of round jets required for the uniform cooling increases as the curvature ratio increases. The details of an experimental study carried out on a single jet and multiple jets emerging from round nozzles of diameter, d and impinging over a uniformly heated cylinder of diameter, D are presented. The number of jets are varied from one to six in the parametric study. In the multi-jet configurations, the jets are arranged circumferentially around the heated cylinder. The range of Reynolds number, Red considered is 5000 – 20,000. The curvature ratio, D/d is varied from 5.1 to 20.4 and the nozzle-to-cylinder spacing, H/d is varied from 2 to 12. The present results show that the Nusselt number at the stagnation point (Nustag) is not affected when the number of jets is increased. However, in multi-jet configurations with four and six jets, the interaction between the wall jets increases heat transfer in the fountain regions. The number of round jets required for the uniform cooling increases with increase in the curvature of the target cylinder, D/d. Based on the experimental study, correlations are given for the stagnation point Nusselt number (Nustag) and average Nusselt number (Nuavg).