An experimental study is performed to investigate heat transfer and fluid flow in two straight, rectangular channels with a 180 degrees sharp bend. Ribs are attached to two opposite walls with an angle of 90 degrees or 60 degrees to the flow. More than 450 thermocouples are used to monitor detailed distributions of local heat transfer coefficients over the four wall surfaces of the entire flow channel. Flow visualization tests are performed which reveal the generation of secondary flows. The impacts of their interaction on heat transfer enhancement and the rib arrangement which gives the highest heat transfer performance are disclosed. Applications to the internal cooling of gas turbine blades are discussed.