Numerical analysis on heat transfer, flow structure and exergy loss of combined truncated and circular ribs in a square duct

Abstract

The heat transfer, friction and exergy loss of a square duct with combined circular and trun-cated rectangular ribs are analyzed using computational fluid dynamics. The study is focused on the effect of rib arrangements on the flow and heat transfer performance. The analysis is carried out with six truncated rib angles varying between 15° and 90° and Re range of 12000 – 43000. The heat transfer is maximum in the middle part of the duct for 30° and 45° rib angles along span wise direction. The position of wake region is highly dependent on separation point over the circular rib as wake moves away radially from the axis of the duct for rib angles of 60°, 75° and 90°. The turbulent flow structures in large scale originates from side wall have marked effect on the heat transfer for the rib angles of 60°, 75° and 90° and with nearly with equal intensity for 15°, 30° and 45° rib angles. The exergy loss associated with friction is higher for 60° rib angle. While the normalized friction factor obtained with Fanning’s equation varied between 1.8 and 4.2 and thermal hydraulic performance varied between 0.2 and 1.3 for the range of reexamined.