Organic Rankine Cycle for Low-to-Medium Temperature Heat Recovery: Working Fluids, Architectures, Expanders, Control, and Deployment Pathways

Abstract

Organic Rankine cycles (ORCs) have matured into a leading technology for converting low-to-medium temperature heat into electricity in applications spanning industrial waste heat, geothermal, biomass, and solar thermal systems. Their competitiveness stems from the ability to match diverse heat-source temperature profiles using organic fluids, flexible architectures (subcritical, recuperated, regenerative, transcritical, and supercritical variants), and compact turbomachinery or volumetric expanders. This review consolidates the state of the art across (i) working-fluid selection under simultaneous thermodynamic, environmental, safety, and cost constraints; (ii) plant architectures and heat-exchanger design that govern pinch losses and off-design behavior; (iii) expander choices from radial turbines to scroll, screw, and piston machines; and (iv) modeling, control, and techno-economic assessment frameworks for robust deployment. The paper synthesizes performance trends drawn from experimental surveys and system demonstrations, highlighting that heat exchangers dominate irreversibilities and dynamic response, while expander efficiency and stable condensation strongly shape net output in small-to-mid scale systems. Recent advances in off-design optimization, moving-boundary dynamics, and supervisory control improve annual energy production and operational reliability. Remaining bottlenecks include fluid regulation transitions, high-temperature stability of “dry” fluids, cost-effective scaling below ~100 kWe, and integration constraints (cooling availability, fouling, and transient heat-source behavior).