Comparative thermodynamic study of refrigerants to select the best for use in the high-temperature stage of a two-stage organic Rankine cycle for RO desalination

A comparison of many organic working fluids was made. Emphasis was given to the efficiency of the thermodynamic cycle using each working fluid, as well as its environmental impact. The thermodynamic cycle consists of two stages: high temperature and low temperature. The maximum temperature of the first one is around 137°C and the second one 77°C. Not all the working fluids had a critical temperature higher than 137EC; therefore, not all could be used under these conditions. The study focused on 33 organic working fluids; according to various criteria that were followed, the most appropriate found was the R245fa. Although it was not the most efficient, nor produced the maximum mechanical work, it performed quite well and, in addition, its use is not restricted by any international regulations. The concept was part of the research within the framework of the project COOP-CT-2003-507997.