Abstract: The heat flow divergence equation is derived to reveal the inherent thermodynamic mechanism for enhancing convective heat transfer . It is found that the two mechanisms, in the case that heat and mass transfer processes are both spontaneous progresses, when mass flow and heat flow are in the same phase , the decreasing of phase difference between mass flow and heat flow, the increasing of heat transfer, which reflects field synergy mechanism of energy transfer between two spontaneous progresses with positive entropy generation rate, while in the case that heat transfer is nonspontaneous process and mass transfer is spontaneous process, when mass flow and heat flow are in the opposite phase, the increasing of phase difference between mass flow and heat flow, the increasing of heat transfer, which reflects the thermodynamic coupling mechanism of energy conversion between spontaneous process with positive entropy generation rate and nonspontaneous process with negative entropy generation rate. Between mass flow and heat flow from the same phase to the opposite phase, corresponding to the energy transfer mechanism of field synergy and the energy conversion mechanism of thermodynamic coupling.

Key words: convective heat transfer, divergence equation, field synergy, thermodynamic coupling