Detailed heat transfer and fluid flow investigation in a rectangular duct with truncated prismatic ribs

The paper presents an experimental study of detailed heat transfer and flow field characteristics in a rectangular duct having different types of truncated prismatic ribs on the bottom surface. The truncated prismatic ribs are manufactured by tapering the square rib from both the sides up to the center to provide rib height at the ends of 0, 2, 4, 6 and 8 mm. Experimental heat transfer results using transient liquid crystal thermography (LCT) are reported along with the mean flow field results using particle image velocimetry (PIV) at a rib pitch-to-height ratio of 10. The heat transfer effectiveness of proposed rib configurations is evaluated by examining the surface- and spanwise-averaged Nusselt number distribution. The effect of rib configurations on the flow parameters as well as on the heat transfer augmentation, with an emphasis to overall averaged augmentation Nusselt number, friction factor ratio, and performance index factors, are studied over a wide range of Reynolds number (9400-58,850). Most of the truncated prismatic ribs provide higher augmentation Nusselt number (about 25.15%) and lower pressure penalty (about 54.65%) than those with the square ribs. The truncated prismatic ribs provide better thermohydraulic performance than the square rib, however, these values are about 25-53% higher respectively at the lowest and the highest Reynolds number. Further, the aero-thermal characteristics are studied and documented in order to enhance the understanding and to correlate the flow dynamic mechanisms with the heat transfer augmentation from the fundamental perspective for all proposed rib configurations at a fixed Reynolds number of 42,500. The combined analysis of aerothermal characteristics puts in evidence the role of fluid dynamic factors i.e. flow features, mean velocities, and the turbulence intensity in the heat transfer augmentation.