Performance of an organic Rankine cycle with multicomponent mixtures

• The performance of an ORC operating with different zeotropic multicomponent mixtures is presented.
• A thermodynamic method is proposed for the design of multicomponent mixtures for ORC power plants.
• High exergy efficiency as well as high volumetric expander work can be achieved with appropriate mixtures.
• The method allows design of mixtures that can be used with off-the-shelf positive displacement expanders.

There is a renewed interest in ORC (organic Rankine cycle) systems for power generation using solar thermal energy. Many authors have studied the performance of ORC with different pure fluids as well as binary zeotropic mixtures in order to improve the thermal efficiency. It has not been well appreciated that zeotropic mixtures can also be used to reduce the size and cost of an ORC system. The main objective of this paper is to present mixtures that help reduce the cost while maintaining high thermal efficiency. The proposed method also allows us to design an optimum mixture for a given expander. This new approach is particularly beneficial for designing mixtures for small ORC systems operating with solar thermal energy. A number of examples are presented to demonstrate this concept.