Turbulent multi-jet impingement cooling of a heated circular cylinder

The experimental and numerical studies of eight circular air jets emerging from a piccolo tube and impinging over a long heated target cylinder of diameter (D), have been presented for both the inline and staggered layouts of holes. The ratio of the diameter of the heated cylinder (D) to the inner diameter of piccolo tube (d(pic)), D/d(pic) is taken as 2.4. The jet Reynolds number, calculated based on the average mass flow rate of a single jet and the diameter (d) of jet holes on a piccolo tube, Re-d = M(in)d/(nA(jet)mu), is varied in the range of 5000 - 20000. The dimensionless distance from the piccolo tube to the target cylinder, H/d is varied from 2 to 12. The dimensionless spacing between two adjacent holes, P-c/d(pic) and the D/d are considered in the range of 1.4 <= P-c/d(pic) <= 2.9 and 5.5 <= D/d <= 17, respectively. The experimental results show that the configuration of multi-jet impingement with D/d = 5.5 cools the circular cylinder more effectively due to higher mass flow rate of jet fluid for the fixed values of Re-d and H/d and P-c/d(pic). Correlations for the average Nusselt numbers are also presented for both the inline and staggered layouts of jets using the experimental results.