Mass∕Heat Transfer in Rotating, Smooth, High-Aspect Ratio (4:1) Coolant Channels With Curved Walls

The paper presents an experimental study of heat∕mass transfer coefficient in 4:1 aspect ratio smooth channels with nonuniform cross sections. Curved leading and trailing edges are studied for two curvatures of 9.06 $m−1$ (0.23 $in.−1)$ and 15.11 $m−1$ (0.384 $in.−1)$ and for two different curvature configurations. One configuration has curved walls with curvature corresponding to the blade profile (positive curvature on both leading and trailing walls) and the other configuration has leading and trailing walls that curve inward into the coolant passage (negative curvature on the leading surface and positive curvature on the trailing surface). A detailed study at Re=10,000 with rotation numbers in the range of 0–0.07 is undertaken for the two different curvature configurations. All experiments are done for a 90 deg passage orientation with respect to the plane of rotation. The experiments are conducted in a rotating two-pass coolant channel facility using the naphthalene sublimation technique. Only the radially outward flow is considered for the present study. The spanwise mass transfer distributions of fully developed regions of the channel walls are also presented. The mass transfer data from the curved wall channels are compared to those from a smooth 4:1 rectangular duct with similar flow parameters. The local mass transfer data are analyzed mainly for the fully developed region, and area-averaged results are presented to delineate the effect of the rotation number. Heat transfer enhancement especially in the leading wall is seen for the lower curvature channels, and there is a subsequent reduction in the higher curvature channel when compared to the 4:1 rectangular smooth channel. This indicates that an optimal channel wall curvature exists for which heat transfer is the highest.