Performance Study on Single-screw Expander in Organic Rankine Cycle System

The selection of expanders for organic Rankine cycle (ORC) systems is very important, because it affects the performance of the system significantly. Single-screw expander is a new type of volume-type expanders, which is very suitable for medium/small scale ORC systems. In order to investigate the performance of single-screw expander in an ORC system, an experimental system is set up which is used high temperature gas as heat source and R123 as working fluid. By adjusting the torque and back pressure of single-screw expander and the vapor dryness of working fluid, the performance of single-screw expander has been obtained. The power output of single-screw expander is 5.46 kW, and the total efficiency and volume efficiency are 48.7% and 80%, respectively. The results shown that under the same heat resource, the expander ratio of single-screw expander increased with the risings of torque and dryness, but it decreased with the increase of back pressure; the volume efficiency decreased with increases of torque and dryness; and the total efficiency of single-screw of expander decreased with increases of back pressure and dryness, and with increase of torque, it increased at first and then decreased after the maximum is gotten.