Local and Average Heat/Mass Transfer over Flat Tube Bank Fin Mounted In-Line Vortex Generators with Small Longitudinal Spacing

Abstract

The local and average heat transfer characteristics over a flat tube bank fin mounted with in-line vortex generators (VGs) with small longitudinal spacing (six VGs per tube) have been studied by using the analogy of heat and mass transfer. Three rows of flat tube and several types of surfaces involved in heat transfer process such as fin surface mounted with VGs, its back surface (mounted without VGs), and flat tube surface are considered. The effects of the fin spacing and VG parameters such as height and attack angle on heat transfer and pressure drop are investigated. The heat transfer performances of flat tube bank fin element mounted with VGs are compared with that without VG enhancement under three constraints. The correlations of Nusselt number and friction factor are given out. The results reveal that VGs can greatly enhance the heat transfer in the region near flat tube on the fin surface mounted with VGs, and in the region away from flat tube wall with some distance on the back surface of the fin mounted with VGs; that the in-line 6 VGs per tube mainly contribute to the increase of heat transfer on the back surface of the fin mounted with VGs; that increases of VG height and attack angle increase the enhancement of heat transfer and pressure drop; that Nusselt number is almost independent of fin spacing with flat tube width as the characteristic length; that small fin spacing causes great increase of pressure drop; and that at identical pumping power and identical pressure drop constraints, fin spacing has the main effect on the increase of heat transfer performance.