Thermodynamic optimization of the match between two streams with phase change

The optimum thermodynamic match between two streams at different temperatures is determined by maximizing the power generation (or minimizing the entropy generation) associated solely with the stream-to-stream interaction. Each stream experiences a change of phase. It is shown that the optimum is marked by an optimal ratio between the stream mass flow rates, and an optimal ratio between the two heat exchanger sizes when the total heat transfer area is fixed. The sensitivity of the optimum relative to the various physical parameters of the two-stream arrangement is documented systematically. The study shows that the optimum is “robust” relative to changes in several parameters such as the distribution of heat transfer coefficient along the hot-end heat exchanger, and the model used for the thermodynamic behavior of steam.