The continual increase in energy demand and environmental problems calls for more and more utilization of sustainable energy. Since the organic Rankine cycle(ORC) is capable of converting low grade thermal energy into electricity

improving energy utilization efficiency and reducing CO2 emissions

it is gradually becoming a hot spot of concern. Expander is the core component of the organic Rankine cycle which directly affects the power generation efficiency

reliability and economy of the system. This paper summarizes various types of expander for low-grade energy utilization ORC system

and reviews their working principle

technical characteristics

research progress and application status. The results show that

comprehensively considering its performance and efficiency

the turbine expander is suitable for the waste heat utilization system with scale of 50 kW

the volumetric expander has obvious advantages in the ORC system with scale of 200 k W

and the screw expander is suitable for the ORC system with scale of 500 kW. For other types of expander

there are more experimental studies and fewer applications at present. During the selection of the expanders

not only the efficiency

but also the application

economy

complexity and post-maintenance cost need to be considered.