Thermal and economic performance analysis of zeotropic mixtures for Organic Rankine Cycles

• Zeotropic mixtures R227ea/R245fa, Butane/R245fa and RC318/R245fa are researched.
• The mixture ORC is compared with the common ORC.
• The influence of temperature glide in ORC is studied.
• The first and second law efficiency for mixture ORC are both calculated.
• The net power output per unit UA based on counter flow is analyzed.

In order to reveal the performance of mixture in Organic Rankine Cycle (ORC), this paper presents the performance of ORC using hot air as heat resource. The zeotropic mixture fluids studied are R227ea/R245fa, Butane/R245fa and RC318/R245fa. The first law efficiency, the second law efficiency, exergy loss distributions and net power output of zeotropic mixture fluids are calculated and compared with corresponding pure fluids. By using the counter flow heat exchangers, the system's economic performance is analyzed based on the net power output per unit UA. The result indicates that better thermal performance can be achieved when the temperature difference of cooling water is near the temperature glide of zeotropic mixture in the condenser; cycle efficiency, exergy efficiency and net power output increase compared to corresponding pure fluid cycles, but the net power output per unit UA decreases; in other words, the economic performance of this system becomes worse in some degree.