Parametric investigation of open-drive scroll expander for micro organic rankine cycle applications

Organic Rankine cycles (ORC) are used to produce power from low-temperature heat sources. In the low power output range (<10 kW(e)), scroll expanders are preferred. However, the performance of the ORC system is dependent on the expander efficiency. The present work focuses on the parametric investigation of the open-drive scroll expander used for micro-organic Rankine cycle. A 5 kW(e), expander was used and its built-in volume ratio was 3.5. R245fa was used as the working fluid. The analysis was carried out using a well-known semi-empirical model available in the literature. Effect of key parameters such as expansion ratio, shaft speed, and expander inlet temperature on power output and expander efficiency wasevaluated for four different cases. Results showed that, at an inlet pressure of 10 bar, peak efficiency of 58% and 60% was achieved at shaft speeds of 1500 RPM and 2000 RPM respectively. It was also evident that,at higher shaft speeds, the increase in mass flow rate is not sufficient to counter frictional and mechanical losses within the expander. The analysis also indicated that increasing the expander inlet temperature could have a negative impact on the expander efficiency as well as the overall performance of the ORC system, as the thermal energy dissipation is higher at higher inlet temperatures for all cases.