The main object of this study is to grasp the heat transfer characteristics of the flow over a backward-facing step in a rectangular duct having side walls. In this experiment, distribution of the local heat transfer coefficient on the bottom wall was measured. The duct tasted has 15 mm height and 240 mm width at the inlet. The aspect ratio and the expansion ratio of the stepped duct were 16 and 2, respectively. Temperature measurement of the wall downstream the step was done using thermo-sensitive liquid crystal method. Reynolds number based on the step height was changed from 200 to 1000 as a parameter. Local heat transfer changes not only in the streamwise direction but also in the spanwise direction. The maximum heat transfer coefficient always appears near sidewall at each Reynolds number due to the downwash flow from the step near the side wall. When the Reynolds number is low, the ratio of the maximum heat transfer coefficient of the entire duct to the maximum one at the center of the duct becomes high. As the Reynolds number increases, the location of the maximum heat transfer coefficient at the center of the duct moves to downstream from Re=200 to 400 and moves to upstream from Re=400 to 1000. This tendency is the same as the behavior of the reattachment point. It was also found that the maximum heat transfer coefficient occurs more downstream than the reattachment point at each Reynolds number.
