A review of organic Rankine cycles (ORCs) for the recovery of low-grade waste heat

The efficiencies of ORCs using cryogens such as benzene, ammonia, R11, R12, R134a and R113 as working fluids have been analyzed parametrically and compared. For operation between two isobaric curves, the system efficiency increases and decreases for wet and dry fluids, respectively, and the isentropic fluid achieves an approximately constant value for high turbine-inlet temperatures. These effects are primarily due to the different slopes and shapes of the saturation vapor curves of the fluids. Isentropic fluids are most suitable for recovering low-temperature waste heat. Freons and their alternatives have been studied and shown similar system responses in ORCs. (C) 1997 Elsevier Science Ltd.