Enhancement of heat transfer in a fin-tube heat exchanger using rectangular winglet type vortex generators

摘要

The present study simulates the air flow through fin-tube type heat exchangers with rectangular winglet pairs (RWP) of half the channel height as vortex generators (VG). The heat exchanger is approximated as a periodic rectangular channel with heated walls and three rows of built-in tubes placed at an appropriate interval. Two different orientations of the tubes in the heat exchangers are considered here - one with inline arrangement of three tube rows and the other with staggered arrangement of three tube rows. Further, the angles of attack in each orientation are varied. The heat transfer characteristics of the heat exchangers with vortex generators located near the tubes have been compared among the cases with varied angles of attack and orientations of tubes. The Navier-Stokes and energy equations along with the appropriate boundary conditions are solved using the ANSYS FLUENT 14.5 solver. Performance parameters in terms of Nusselt number, vorticity and quality factor (a ratio between the Colburn factor to apparent friction factor, also refer to as area goodness factor with slight modification) were evaluated. The results show significant improvement in the heat transfer performance due to the nozzle-like flow passages created by the winglet pair and the region behind the circular tube which promote accelerating flow. There is an increasing trend of the above for the in-line row of tubes; whereas with the staggered row of tubes, there is slight deviation of this trend. Due to the alternate CFD-CFU orientations of the VG, the performance improves with increase in angle of attack up to a certain point and afterwards it is going down.