Performance evaluation of an Organic Rankine Cycle (ORC) for power applications from low grade heat sources

In this paper the performance of an Organic Rankine Cycle (ORC) module, which was designed and built for a specific power application, is experimentally characterized. The ORC tested satisfies the main specifications for an efficient power system, highlighting a volumetric expander with large built-in volume ratio. For tests development, a monitored test bench has been used and adapted to the planned test procedure, which consisted of varying the thermal power input for different condensing conditions. Thereby, 10 steady state points are achieved and analyzed according to thermal power input, gross and net electrical powers, electrical cycle efficiencies and expander effectiveness. The results show that the ORC performances are improved for higher thermal oil temperatures, capturing more thermal power, producing more electricity and achieving better cycle efficiencies. The maximum gross electrical efficiency obtained is 12.32%, for a heat source temperature about 155 °C and a direct dissipation to the ambient. Moreover, the expander reaches an electrical isentropic effectiveness about 65% for an optimum pressure ratio around 7, being a suitable system for power applications from low grade heat sources.