Field synergy principle is based on the steady state laminar thermal boundary layer integral equations and has been validated by the experimental data and numerical simulations.However

at present

the descriptions for the general relation between the field synergy angles in different scopes and the nature of additional equivalent source and the mechanism for the two effects to enhance or weaken the heat transfer processes are lacking

which are essential for control of the field synergy heat transfer process.In this study

a universal theory for the field synergy principle is obtained through the analysis and establishing an equation for the total heat flux density vector divergence.The results show that the field synergy changes the divergence.Since the divergence reflects the relation between the source in the region and the flow on the border

the analysis of the effect of field synergy angle change on the divergence may identify the nature of additional equivalent source

as well as the change of volume and direction of the total heat flux density vector

so that the mechanism for heat transfer process to be enhanced or weaken is revealed.