Investigations on experimental performance and system behavior of 10 kW organic Rankine cycle using scroll-type expander for low-grade heat source

Abstract

In this study, experimental characteristics of a 10 kW organic Rankine cycle (ORC) with R245fa were investigated for low-grade waste heat recovery. A semi-hermetic scroll-type expander was utilized with proper lubrication. The conductive oil loop using electric heaters was to simulate low-grade heat source. The temperature and heat power of the heat source were set to 120 °C and 34–77 kW, respectively. Results showed that pressure ratio and degree of superheating exhibit high sensitivity on system performance. The trend of isentropic efficiency for expander presented decreasing with pressure ratio in rise, while pressure ratio for the inlet and outlet of the expander is larger than 4. In addition, there is a particular phenomenon existing under low pinch point temperature. Mass flow rate and pressure ratio exhibited periodic distribution with time, while the pinch point temperature is lower than 10 °C. It means that the pinch point temperature has a critical value, which leads to the supply of heat source not under stable situation for low pinch point temperature. This phenomenon of thermal fluctuation may result in reduce useful life for system components. The maximum measured electrical power, net thermal efficiency and net electricity efficiency are 6.2 kW, 8.9% and 7.9%, respectively. As a consequence, the electricity generation and net electricity efficiency could be further raised while the simulated heat power increases based on the present efforts. The present work demonstrates the potential of scroll-type expander for the small-scaled ORC applications, such as industrial waste heat recovery, geothermal energy.