Several problems in thermodynamic calculation of surface air coolers

Discusses the application of the two commonly used conclusions in the thermodynamic calculation of surface air coolers, i.e.  “the same enthalpy of inlet air, the same enthalpy of outlet air” and “the mean coil surface state is on the line of the state points of the inlet and the outlet air ”. Verifies them according to the thermodynamic calculating formulas. Points out that the mean coil surface state is approximatively existent under wet conditions. Discusses the shortcoming and rationality of the method of judging work conditions by mean coil surface state. Puts forward a method to judge work conditions of the fully dry, partially dry and fully wet. Analyses and demonstrates the method by a detailed calculation.