Design of a rotary expander as an expansion device integrated into organic Rankine cycle (ORC) to recover low-grade waste heat

Abstract

An experimental and numerical study on a rotary expander derived from a rotary engine for an organic Rankine cycle was carried out to recover low-temperature and small-scale waste heat. In this study, a rotary expander having a pentagonal rotor was developed to recover low grade heat efficiently. First, the performance of the rotary expanders having a triangular rotor and a pentagonal rotor was numerically analyzed. The amount of power generated by the rotary expander having a pentagonal rotor was 80% greater than that having a triangular rotor. Although the displacement volume ratio of the expander having a triangular rotor was higher than that having a pentagonal rotor, the pentagonal rotor had more working chambers per revolution. Therefore, the amount of power generated by the expander having the pentagonal rotor was large. Then, the rotary expander having a pentagonal rotor was manufactured and integrated into the organic Rankine cycle system. The organic Rankine cycle system was designed to recover low-grade waste heat at a temperature below 70 °C and small-scale waste heat below 10 kW. The amount of power generation by the expander was 140 W and the efficiency of the system was 1.7% when the pressure ratio was 2.4. The performance of the system was expected to increase as the pressure ratio increases. The result showed the possibility of increasing the amount of waste heat recovery by introducing the rotary expander as a power generation device in the organic Rankine cycle system.