Abstract: In order to obtain the working condition of minimum heat transfer entropy increase and to avoid the maximum entropy increase, the method of minimum entropy increase based on temperature and enthalpy analysis is proposed. Firstly, with the extreme values of the entropy increase as benchmark, the expression is deduced on the basis of the relationship between temperature and enthalpy. Then, the relationships between temperature and enthalpy of the two heat transfer fluids are fitted. With a constant logarithmic mean temperature difference, the C language program is compiled to compute the heat transfer conditions of condensations of the carbon dioxide transcritical cycle and R407C heat pump cycle. The results indicate that the minimum heat transfer entropy increase will be obtained when the heat transfer temperature differences approach to the logarithmic mean temperature difference at both ends of the heat exchanger, or the cold fluid side is nearly isothermal and the outlet temperature of hot fluid is close to the inlet temperature of cold fluid. While the maximum heat transfer entropy increase will be obtained when the heat transfer fluids on both sides are isothermal; when the entropy increase with unit heat transfer rate at the pinch point is small and shows small-scale fluctuations, the system entropy increase with unit heat transfer rate will present large range fluctuations. In general, the smaller the entropy increase with unit heat transfer rate at the pinch point is, the smaller the system entropy increase with unit heat transfer rate will be. This method is not only used to forecast the working condition of minimum energy loss, but also provides a reliable theoretical way for establishing the standard design conditions of heat exchangers.

Key words: Exergy loss, Heat transfer fluids Temperature matching, Minimum entropy increase, Temperature and enthalpy analysis