Characteristics of turbulent flow and heat transfer in a rectangular channel with repeated rib roughness

Characteristics of heat transfer and turbulent flow over a repeated-rib-geometry, rough-wailed surface were investigated in connection with a two-dimensional square rib roughness that was put on the top and bottom surfaces in a rectangular channel. The experiments were performed on three types of rib configuration. The duct flow Reynolds number was set. which was similar to the condition for practical heat exchanger tubes. Flow measurements were performed using a fiber laser Doppler velocimeter. The results of the detailed flow measurements indicated that a recirculating flow existed behind the rib on symmetric and staggered rib geometries. A remarkably large peak value of Reynolds shear stress was observed behind the rib on the staggered rib geometry. The flow measurements show that the feature of turbulent flow structure was well correlated with the heat transfer characteristics over the ribbed wall.