Heat Transfer Enhancement and Pressure-Loss Reduction for Fin-Surfaces of In-line Tube Bundle with a Single Front Row of Winglet Pairs.

Abstract

This paper proposes a novel technique that can augment heat transfer but nevertheless can reduce pressure-loss in a fin-tube heat exchanger with circular tubes in a relatively low Reynolds number flow, by deploying a single row of the delta winglet type of vortex generators beside the front row of the three-row tube bundles in an in-line arrangement. The winglets are placed with a heretofore-unused orientation for the purpose of augmentation of heat transfer. This orientation is called as “common flow up” configuration. The proposed device causes a significant separation delay, reduces form drag, and removes the zone of poor heat transfer from the near-wake of the tube. This enhancement strategy has been successfully verified by experiments in the proposed configuration. In the in-line tube bundle with three rows, the heat transfer was augmented by 10% to 20%, and yet the pressure loss was reduced by 8% to 15% for the Reynolds number (based on two times channel height) ranging from 350 to 2100, when the present winglets were built in a single front row.