Wake Management and Capacity Augmentation by Toe-Out Type Vortex Generators in Finned-Tube Heat Exchangers

Abstract

Waste heat recovery usually involves indirect heat transfer, between two fluids, across a diathermic wall; and finned-type recuperative heat exchangers are preferred for the stipulated task. Strategic integration of vortex generators in aforesaid systems produces such flow structures which greatly improve the effectiveness of the heat exchanger. Often heat exchanger designers place generators at under-performing locations, despite knowing the best ones, due to manufacturing restrictions. Since the generators' geometry too affects the thermal augmentation, positional compromise can be duly compensated. This study uses a computational analysis to investigate the effect of varying the geometric aspect ratio of the generators. For a conclusive assessment of the geometric designs, the attack angles espoused for integrating the generators cater to the entire effective range. In order to understand the changes in flow characteristics, velocity fields are examined which suggests that reducing the generators' aspect ratio aids in diverting the oncoming flow, and so limits the tube wake zones. Additionally, the swirling flow generated by the vortex generators facilitates bulk mixing across a large fin surface. Both flow modifications together give a substantial boost to the thermal performance, thereby downsizing the system.