Heat transfer enhancement from a surface affixed with rectangular fins of different patterns and arrangement in duct flow

Experiments were performed to investigate the heat transfer and fluid flow characteristics of a surface with arrays (7 x 7) of short rectangular plate fins of four different fin patterns co-angular, zigzag, co-rotating, and co-counter rotating - for air flow (Re = 15,700104,500) in a duct. T-type thermocouples and an infrared camera with a 160 x 120 point In - Sb sensor were used to measure the temperature and the detailed heat transfer at the endwall along with the fin base. A flow behavior and its effect on heat transfer were observed from smoke flow visualization and oil titanium oxide film flow techniques. Horseshoe vortices were formed in front of the fins and longitudinal vortices were generated by the side top edges of the fins while behind the fins rolled-up vortices appeared in every fin pattern. Among the four patterns, the largest friction factor occurred for the co-rotating pattern at a smaller pitch ratio owing to strong flow interactions and combined vortex attack on the endwall and fin surface whereas the least friction developed for the co-angular pattern. The heat transfer result shows that the co-rotating pattern has the highest Nusselt number and the co-angular pattern has the least Nusselt number. Considering the thermal performance, the co-rotating pattern with a smaller pitch ratio is found to be the most recommended pattern as the heat transfer augmentation with the co-rotating pattern is more than three times the finless duct.