Heat/mass transfer in rotating, smooth, high aspect-ratio (4:1) coolant channels with curved walls

The thesis presents an experimental study of heat/mass transfer coefficient in 4:1 aspect ratio smooth channels with non-uniform 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 inwards into the coolant passage (negative curvature on the leading surface and positive curvature on the trailing surface). 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 span-wise mass transfer distributions of fully developed regions of the channel walls are also presented, to delineate the effect of rotation number. The mass transfer data from the curved wall channels is compared to those from a smooth 4:1 rectangular duct with similar flow parameters. In the first set of experiments Re=10,000 with Ro=0-0.071 and 90 degree orientation, 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 at this Reynolds number for which heat transfer is the highest. For Re=20,000 with Ro=0-0.051 and 90 and 45 degree orientation, the heat transfer results show highest enhancements for the higher curvature positive-positive section, with respect to the 4:1 rectangular channel, but this enhancement is reduced with increase in rotation. The lower curvature positive-negative section shows the highest increment in heat transfer enhancement with rotation number for both 90 and 45 degree orientations. The heat transfer ratios are reduced with rotation for the 45 degree orientation for the higher curvature positive-negative section. Thus, all the measurements indicate that an optimum curvature exists for a particular Reynolds number where the heat transfer would be the highest

GT2006-90052 MASS/HEAT TRANSFER IN ROTATING, SMOOTH, HIGH-ASPECT RATIO (4:1) COOLANT CHANNELS WITH CURVED WALLS

ABSTRACT The paper presents an experimental study of heat/mass transfer coefficient in 4:1 aspect ratio smooth channels with non-uniform cross-sections. Curved leading and trailing edges are studied, for two curvatures of 9.06 m -1 (0.23 in ) 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 inwards 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 o 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 span-wise mass transfer distributions of fully developed regions of the channel walls are also presented. The mass transfer data from the curved wall channels is compared to those from a smooth 4:1 rectangular duct with similar flow parameters. The local mass transfer data is analyzed mainly for the fully developed region, and areaaveraged 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