Performance analysis of organic Rankine cycle based on location of heat transfer pinch point in evaporator

• Model seeking the location of heat transfer pinch point in evaporator of ORC is established.
• The matching coefficient between heat source and working fluid can be revealed based on pinch point.
• Performances of subcritical and supercritical ORCs are investigated using trough solar collector as heat source.
• The optimal initial pressure and maximum work output are obtained with and without IHX in cycles.

The location of heat transfer pinch point in evaporator is the base of determining operating parameters of organic Rankine cycle (ORC). The physical mathematical model seeking the location of pinch point is established, by which, the temperature variations both of heat source and working fluid with UA can be obtained. Taking heat source with inlet temperature of 160 °C as example, the matching potentials between heat source and working fluid are revealed for subcritical and supercritical cycles with the determined temperature difference of pinch point. Thermal efficiency, exergy efficiency, work output per unit area and maximum work outputs are compared and analyzed based on the locations of heat transfer pinch point either. The results indicate that supercritical ORC has a better performance in thermal efficiency, exergy efficiency and work output while outlet temperature of heat source is low. Otherwise, subcritical performs better. Small heat transfer coefficient results in low value of work output per unit area for supercritical ORC. Introduction of IHX may reduce the optimal evaporating pressure, which has a great influence on heat source outlet temperature and superheat degree. The analysis may benefit the selection of operating parameters and control strategy of ORC.