Heat transfer and pressure drop in hexagonal ducts with surface dimples

Measurements of detailed Nusselt number (Nu) distributions and pressure drop coefficients (f) for four hexagonal ducts with smooth and dimpled walls are performed to comparatively examine the thermal performances of three sets of dimpled walls with concave–concave, convex–convex and concave–convex configurations at Reynolds numbers (Re) in the range of 900–30,000. A set of selected experimental data illustrates the influences of dimple configuration and Re on the detailed Nu distributions, the area-averaged Nu   over developed flow region (Nu¯) and the pressure drop coefficients. Relative enhancements of Nu and f from the smooth-walled references (Nu∞ and f∞) along with the thermal performance factor (η  ) defined as (Nu¯/Nu∞)/(f/f∞)1/3 are examined. Nu¯ and f correlations are individually obtained for each tested hexagonal duct using Re as the controlling parameter.