Heat Transfer Coefficients in an Orthogonally Rotating Duct With Turbulators

Experiments were conducted to determine the influence of rotation on local heat transfer coefficient for the turbulent flow in a short square duct (L/D_H = 15) with a pair of opposite rib-roughened walls. The ribs are configured in an in-line arrangement with an attack angle of 90 deg to the main flow. The coolant used was air with the flow direction in the radially outward direction. The Reynolds numbers ranged from 5000 to 25,000; the rib pitch-to-height ratio was 5; and the rib height-to-hydraulic diameter ratio was kept at a value of 0.20. The rotation number range was 0 to 0.5. Local Nusselt number variations along the duct were determined over the trailing and leading surfaces. In addition, local heat transfer measurements on all sides of a typical rib as well as on a typical exposed base surface between two consecutive ribs in a fully developed region were conducted at various rotational speeds. It is shown that the Coriolis acceleration tends to improve the heat transfer due to the presence of strong secondary flow. Centripetal buoyancy is shown to influence the heat transfer response with heat transfer being suppressed on both leading and trailing surfaces as the wall-to-coolant temperature difference is increased with other controlling parameters hold constant. Results are also compared with previous investigations. It was found that the results agree very well with those reported by other works in this field.