Heat Transfer for Round Air Jets Flowing Along a Concave Surface

Local Nusselt number distributions for a square array of round air jets impinging on a flat surface and a concave surface were measured in high resolution by naphthalene sublimation techniques. Corresponding numerical simulations using a realizable k-ε model were also conducted to investigate the heat transfer characteristics of the multiple jets and to clarify the complex flow structure. The experiments were conducted for Re = 5000, 10000, and 15000 at the non-dimensional nozzle to plate distance of 3.75. The Nusselt number for both flat and concave surfaces increased as Reynolds number increased from 5000 to 10000. Unexpectedly, experimental results showed the tendency of Nu to be saturated for Re = 15000, while showing a monotonic increase in numerical simulations. Most amount of wall jets from a central impinging jet formed large-scale recirculating flows, which surrounded free jet region of each jet, while some other wall jet were entrained by a small vortical structure near the target wall and merged into large-scale recirculating flow of the neighboring jets.