Convective Heat Transfer and Absolute Vorticity Flux along Main Flow in a Channel Formed by Flat Tube Bank Fins with Vortex Generators Mounted on Both Fin Surfaces

Tube bank fin heat exchangers are employed in a wide variety of engineering applications. If vortex generators (VGs) are mounted or punched onto fin surfaces, heat transfer can be enhanced even if the height of the VG is small. The role of VGs is to produce longitudinal vortices along the main flow, and vortices are kinds of secondary flows. It is still not clear why a secondary flow can enhance heat transfer efficiently, and we lack a parameter that can be used to specify its intensity. In this paper, cross-averaged absolute vorticity flux in the main flow direction is used to specify the intensity of the secondary flow produced by the VGs mounted on both surfaces of the fin. The relationship between the intensity of the secondary flow and the strength of convective heat transfer is studied using a numerical method. The results reveal that cross-averaged absolute vorticity flux in the main flow direction can reflect the intensity of a secondary flow. For the case studied, there is a strong relationship between this cross-averaged absolute vorticity flux and the span-averaged Nusselt number. One would expect that the cross-averaged absolute vorticity flux along the main flow can be used to check the suitability of the arrangement of the VGs on the fin surfaces.