Eq. (14) is a new momentum equation with an additional force, and it is derived when the exergy destruction is the least on the condition of constant fluid power consumption. So the velocity field satisfying the equation will lead to the best performance of heat transfer. That is to say, any other forms of velocity field has worse performance of heat transfer when the fluid power consumption is constant. In Eq. (14), the additional force consists of constant coefficient, unknown scalar and temperature gradient, so it is related to the temperature field and it reflects the influence of temperature field on the flow field. This force will drive the fluid flow in synergy with the heat transfer. In other words, this force will drive the fluid to flowalong the direction of the temperature gradient. Besides, the force is obtained when the exergy destruction is the least, so the performance of heat transfer is the best when the flow is under the action of the additional force. The force is virtual because it comes from the mathematical optimization, so the flow resistance will not be high. The optimum pattern of velocity field will be obtained by solving the new momentum equation and it indicates the basic characteristics of the flow pattern which benefits the heat transfer mostly. If similar velocity field can be formed by any enhancemen unit, it will have a very satisfactory performance in heat transfer and flow resistance.