Entransy is a physical quantity describing heat transfer ability, and heat transfer is accompanied by entransy transfer. Thermal energy is conserved in its transfer process, while entransy is dissipated because of the irreversibility of its transfer process. As a result, entransy transfer must have its rules which are different from those of thermal energy transfer. Based on the definition of entransy, an entransy transfer equation is derived, which describes the entransy transfer processes of a multi-component viscous fluid subject to heat transfer by conduction and convection, mass diffusion and chemical reactions. The expressions of entransy flux and entransy dissipation are obtained simultaneously, and their physical mechanism is clarified. And further, the theory and method of optimizing heat transfer applying the entransy transfer equation to the steady-state convection heat transfer process are expounded. The minimum thermal resistance principle and the entransy dissipation extremum principle are obtained by applying the steady-state entransy transfer equation to the steady-state convection heat transfer process. The cases of the single-component steady-state convection heat transfer and the steady-state heat conduction show the application of the theory and method.
