The secondary flow is frequently used to enhance the convective heat transfer. In this paper, the cross-averaged absolute vorticity flux in the main flow direction is used to specify the intensity of the secondary flow produced by vortex generators that are mounted on a three-row flat tube bank fin surfaces. 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 the secondary flow; a significant relationship between this cross-averaged absolute vorticity flux and span-averaged Nusselt number exists for the case studied. This cross-averaged absolute vorticity flux can account only for the secondary flow effects on convective heat transfer but cannot quantify the effects of developing boundary layer on convective heat transfer. (C) 2009 Published by Elsevier Ltd.