A numerical investigation of flow and heat transfer in rotating U-shaped square ducts

Three-dimensional incompressible viscous flow and heat transfer in a rotating U-shaped duct with a square cross-section are studied numerically. The governing equations including full Navier–Stokes and energy equations are solved using a finite volume method based on the SIMPLER algorithm in an orthogonal uniform grid. The effects of wall curvature and rotation on the flow field and heat transfer considering different directions of rotation are presented in detail. The results show that in the bend region, the centrifugal forces due to curvature are significant, performing an intensive outward secondary flows resulting in an increase of heat transfer on the outer wall. But in the straight parts of the duct, secondary flows due to Coriolis forces are dominant. The comparison of numerical results at different rotation angles indicates that the maximum heat transfer rate occurs when the duct rotates about an axis parallel to the axis of duct curvature, at which both the Coriolis and the centrifugal forces intensify each other, while the minimum heat transfer rate takes place in the negative diagonal axis of rotation with angles of α = 180 and β = 135 .