An experimental study on heat-transfer in separated, reattached, and redevelopment regions behind a double step at entrance to a flat duct is presented. Measurements of turbulent fluctuation in a free shear layer are made by using a hot-wire anemometer. The experiments are carried out under a condition of uniform heat flux with the test fluid of air. Reynolds number ranges approximately from 4 × 103 to 2.5 × 105 and a step height ratio h/L is varied between 0.035 and 7.0. It is found that the heat-transfer rate in the separated region is closely connected with the behavior of transported heat to be represented by the product of velocity and temperature fluctuations in the free shear layer. An empirical equation is also proposed for the local Nusselt number in the separated and reattached regions.

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