Heat flux convection transfer equation is used to reveal the enhanced transfer mechanism of normal heat flux on fin surfaces of tube bank fin heat exchanger with vortex generators (VGs) under uniform wall temperature. It is found that no matter whether the vortex generators exists or not, the contribution of the velocity and velocity gradient on the upper and lower fin wall to the normal heat flux transfer mechanism on the wall is zero, and the heat flux transfer on the wall is a diffusion process. In the flow field, because the contribution of velocity and velocity gradient to the wall normal heat flux transfer mechanism is not equal to zero, the heat flux transfer is a convective process. The fin wall normal component q_z is the largest, the transmission intensity of q_z is the largest, and the convective heat transfer intensity is the strongest. In the flow field, the values of q_x and q_y are very small, while q_z is large. The normal heat flux transfer intensity q_z decreases along the direction of the upper and lower wall moving towards the center, and the transfer intensity q_z on the upper wall is stronger than that on the lower wall. The local values of velocity contribution, velocity gradient contribution, velocity and velocity gradient contribution, and heat flux of the flat tube wall, upper and lower walls and the area around the vortex generators are large, and weaken along the main flow direction. Far away from the flat tube wall, the velocity contribution, velocity gradient contribution, velocity and velocity gradient contribution, and the local value of heat flux of the upper and lower walls and the area around the vortex generator are small, and the weakening along the main flow direction is not obvious. Thus, the mechanism of convective heat transfer on the fin surface of flat tube and fin heat exchanger with and without vortex generator is revealed. The results of this study also indicate that VGs enhance heat transfer characteristics near the lower and upper surfaces of the fins, i.e., VGs only exhibit a characteristic of "local enhancement." In regions far from the lower and upper surfaces of the fins, the heat transfer enhancement effect is even less than that without VGs, even with VGs present. Without VGs, except for the relatively large Cq_z values at the leading edge where the flat tube appears and the trailing edge where it disappears, the Cq_z values are small at other locations along the mainstream direction. With VGs, the Cq_z values are influenced not only by the leading edge where the flat tube appears and the trailing edge where it disappears, but also by the leading and trailing edges of the VGs. Comparatively, the leading edge of the flat tube has a greater impact on the Cq_z value than the trailing edge, and the influence of downstream vortices is greater than that of upstream vortices. At the upstream VGs, downstream VGs, and each flat tube, the Cq_z values exhibit periodic fluctuation trends. Regardless of the presence or absence of VGs, in the "local enhancement" regions near the lower and upper surfaces of the fins, the cross-sectional average value of Cq_z increases with increasing Re. Conversely, in the non-"local enhancement" regions far from the lower and upper surfaces of the fins, the cross-sectional average value of Cq_z decreases with increasing Re. However, within both the "local enhancement" and non-"local enhancement" regions, changing the VG length l and the attack angle β has almost no effect on the cross-sectional average value of Cq_z. The larger the height of the VGs, the larger the region where the cross-sectional average value of Cq_z is greater than that without VGs, meaning the "local enhancement" region increases.
 

heat transfer, Convective Heat Transfer, heat flux, vortex generator, tube bank fin, uniform wall temperature, local enhancement region