Thermal matching and performance analysis of an organic Rankine cycle experimental system using R1233zd(E) and variable-frequency pumps

Efficient utilization of low-grade heat is an important pathway toward sustainable electricity generation. In this study, a 2 kW organic Rankine cycle (ORC) experimental system employing R1233zd(E) and dual variable-frequency pumps was developed to investigate the effects of coordinated heat source and working-fluid flow regulation on thermal matching and system performance. The results show that increasing the heat source flow rate improves heat supply, evaporation, and superheating, whereas increasing the working fluid flow rate raises mass throughput and evaporating pressure but may deteriorate thermal matching under excessive flow conditions. A heat matching supply-demand ratio (Φ_Q) was introduced to characterize the coordinated-flow matching condition. By combining Φ_Q with the evaporator pinch-point temperature difference (PPTD), the thermodynamic feasible region was identified, and its lower boundary was found to correspond to approximately Φ_Q = 0.5. Furthermore, the preferred operating region was determined from the overlap between the regions with electricity generation higher than 80% of the maximum power output and electricity-generation efficiency higher than 80% of the maximum efficiency. Under the present experimental conditions, the maximum electricity generation and electricity generation efficiency reached 2.1 kW and 6.2%, respectively, while the corresponding preferred operating region was mainly distributed within Φ_Q = 0.7–1.1. The results demonstrate the effectiveness of coordinated flow regulation for improving the energy-conversion efficiency, highlighting the potential of R1233zd(E)-based ORC systems for efficient low-grade heat recovery.