Heat transfer characteristics from in-line arrays of free impinging jets

An experimental investigation of the convective heat transfer on a flat surface in a multiple-jet system is described. A thin metal sheet was heated electrically and cooled from one side. On the other black coated side the temperature field was measured using an IR camera. Varied parameters were the jet Reynolds number in the range from 1,400 to 41,400, the normalized distance nozzle to sheet H/d from 1 to 10, and the normalized nozzle spacing S/d from 2 to 10. A geometrical arrangement of nine nozzle in-line arrays was tested. The results show that the multiple-jet system enhances the local and average heat transfer in comparison with that of a single nozzle. A maximum of the heat transfer was found for the normalized spacing S/d = 6.0. The normalized distance H/d has nearly no effect on the heat transfer in the range 2 ≤ H/d ≤ 4. The maximum average Nusselt number was correlated as a function of the jet Reynolds number