Enhancing convective heat transfer, by strengthening fluid disturbance, is an effective way of raising the utilization efficiency of an energy system. In this study, in order to introduce a principle for convective heat transfer enhancement, a physical quantity called available potential was defined, and an equation of available potential was derived to obtain an expression of local exergy destruction caused by heat transfer and fluid flow. Then, a mathematical model of convective heat transfer optimization was established by adopting adequate objective function and constraint condition based on exergy destruction minimization, and an optimal flow field of longitudinal whirling flow with multi-vortexes was obtained by solving the optimization controlling equations. Finally, through numerical simulation and a PIV experiment, a heat transfer unit consisting of center-connected awl-shaped slices was studied to realize longitudinal whirling flow with multi-vortexes in a tube, which indicated an excellent effect of heat transfer enhancement. (C) 2018 Elsevier Ltd. All rights reserved.