Performance Optimization and Experimental Investigation of Organic Rankine Cycle System Using Binary Zeotropic Mixtures

Abstract This study proposes a novel optimization method to enhance the behavior of organic Rankine cycle (ORC) systems through utilizing zeotropic mixtures with temperature glide characteristics. The mixture is created by introducing a pure fluid with thermodynamic behavior similar to the target medium but capable of producing a larger temperature glide. Using R245fa as the reference fluid, the behavior of the candidates was examined through simulations and further validated on an experimental ORC test bench. Results show that the ORC system achieved its optimal behavior when the heat source, cooling water, and cycle medium mass flows are 4240 kg/h, 3000 kg/h, and 700 kg/h, respectively. Under these conditions, the turbine enthalpy drop reaches 10.29 kJ/kg, the net output power is 1.919 kW, and the thermal and exergy efficiencies are 12.6% and 3.53%, respectively. With the cycle medium flow range of 500–700 kg/h, the 0.3R134a/0.7R245fa mixture delivers consistently higher efficiencies than pure R245fa, confirming the mixture's performance advantage under practical low-temperature waste-heat conditions.