Analysis of zeotropic mixtures used in high-temperature Organic Rankine cycle

• Using mixtures leads to an efficiency increase compared to pure fluids.
• MM/MDM (0.4/0.6) produces optimal cycle efficiency.
• Lower temperature gradients of heat source and sink give rise to higher cycle efficiency.
• Condensation step shows more effect than evaporation step on cycle efficiency.

The paper investigates the performance of high-temperature Organic Rankine cycle (ORC) with zeotropic mixtures as working fluid. A numerical model, which has been validated by comparing with the published data, is developed to predict the first law thermal efficiency of the cycle. The effects of mixture concentration, temperature gradient of the heat transfer fluid, pinch temperature difference, pressure ratio, and condensation pressure on the first law efficiency are presented firstly using a purposely designed program, and then the suitable conditions for the described ORC are suggested based on the results of the simulation. It is demonstrated that the use of zeotropic mixtures leads to an efficiency increase compared to pure fluids.