Based on the second law of thermodynamics for an open system under non-equilibrium state an intensive analysis of the entropy generation in the process of falling film evaporation was made.A quantitative correlation was deduced to calculate the unit entropy generation number

Ns from the traditional Reynolds number and other parameters under the condition of Re>1450(cpμ/λ)-1.06(0.5-0.25ω)-1.It was unveiled that Ns decreased with decreasing thickness of the falling film and increased after the optimal ω

which corresponded with a minimum value of Ns.The good agreement between the expressions of correlation and the results obtained from an experimental rig of falling film evaporation for phosphoric acid concentration in a vertical heated tube with the dimension of φ30×2×6000 demonstrated that the correlation equation could be rationally used to predict the entropy generation in falling film evaporation.This theoretical prediction

calculated from ordinary thermal process parameters is useful in enhancement of thermodynamic efficiency in industrial processes.