The first law of thermodynamics indicates that energy is conserved. But processes like heat transfer or conversion from heat
to work have certain directions and limitations under specific conditions. Researches on irreversibility of process can reveal the essence of process directions. According to the second law of thermodynamics, entropy can express the irreversibility of physical processes. Bejan [32] analysed and proposed the expression of entropy generation in convective heat transfer. According to thermodynamics, the equilibrium equation for the incompressible fluid can be written as