Energy and exergy analysis of a novel triple-tube-based organic Rankine cycle for combined heat and power generation

Abstract

The present study conducted an energetic and exergetic analysis of a novel ORC-CHP system that integrates a triple-tube evaporator. This design replaces conventional ORC evaporators, channeling hot fluids through the inner annular and normal fluid through the outer annular, and uses isopentane as the working fluid in the inner tube. The investigation focused on the effects of pinch point temperature difference (PPTD), condenser and evaporator temperatures, and hot fluid mass flow rate variations (1–5 kg/s) on system parameters such as network output, total irreversibility, exergetic efficiency, and heat transfer rates. The results revealed a significant impact of PPTD and temperature adjustments on system performance. With a PPTD shift from 3 °C to 10 °C, condenser and evaporator heat transfer rates dropped by 69.98%. A PPTD of 3 °C yielded higher condenser heat transfer and a network output of 3.29 kW with an exergy input of 21.55 kW. The lowest heat transfer rates were observed at 10 °C PPTD, 45 °C evaporator, and 38 °C condenser temperatures. The optimal performance occurred with a condenser at 28 °C and an evaporator at 45 °C, where higher heat transfer rates of 38.29 kW (condenser) and 41.52 kW (evaporator) were achieved. Additionally, as the hot fluid flow rate increased from 1 to 5 kg/s, evaporator and condenser irreversibility rose by 400% and 224%, respectively. In summary, this study demonstrates that the triple-tube evaporator design in ORC-CHP systems achieves higher efficiency by reducing heat transfer losses and irreversibility, thereby overcoming technical barriers and expanding the potential of ORC applications in combined heat and power systems. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.