Investigation of heat transfer and fluid flow behavior between straight and inclined fins in tall duct

This paper describes the flow behavior and flow patterns developed by straight and inclined fins and their affect on heat transfer characteristics. A detailed experimental investigation of the heat transfer and flow characteristics of finned surfaces was conducted for airflow (Re = 3824-12,747) in a tall duct corresponding to 200 mm height. In this experiment short rectangular fins were attached in 7 × 7 arrays to a heating surface and exposed to airflow. T-type thermocouples and an infrared camera with a 160 × 120-point In-Sb sensor were used to measure the wall temperature and to get the detailed heat transfer coefficient over the endwall and fin base. A thermal image and the iso-heat transfer coefficient contour give a complete picture of the heat transfer characteristics of the endwall surface. Smoke flow visualization reveals the longitudinal vortex generated by the inclined fins which significantly enhances the heat transfer in the inter-fin region and the fin surfaces. From the time averaged velocity profiles and spanwise velocity distributions a non-continuous curve caused by the detachment or reattachment of the flow was observed which confirms the existence of a longitudinal vortex in the case of inclined fins. But the horseshoe vortex appeared for both straight and inclined fins. The Nusselt number shows that heat transfer enhancement at a factor of more than three times than the finless duct is achieved for the inclined fins whereas straight fins could reach upto an enhancement of more than two times.