k-ω SST (shear stress transport) two-equation turbulence model was used to analyze the flow and heat transfer characteristics in rotating square U-duct at different inlet Reynolds numbers (10000~60000) and rotation numbers (0~2.013). Results show that both in stationary and rotating state

Nusselt numbers are augmented with the increase of inlet Reynolds number. Comparing with stationary state

at the same Reynolds number

the intensity of heat transfer in radial outward passage is dramatically enhanced by rotating

while the radial inward passage is just enhanced a little. Rotation number influences the U-duct heat transfer through changing the values of Coriolis force and buoyancy force. Coriolis force enhances greatly the heat transfer of trailing surface in radial outward passage

while the leading surface weakens. Buoyancy force causes flow separation in the vicinity of the wall

so it alters the heat transfer characteristics. In different positions of the radial inward passage

the heat transfer intensity of the leading surface firstly decreases and then increases with the rise of rotation number. The critical rotation numbers got by calculation are in good agreement with the experimental results. The product of dimensionless distance parameter and critical rotation is a constant.