Experimental study on an open-drive scroll expander integrated into an ORC (Organic Rankine Cycle) system with R245fa as working fluid

• Only a few experimental studies reported in the literature on oil free scroll expander.
• This paper shows performance measurement (isentropic efficiency, shaft power) of a small scale oil free expander.
• A performance map of the expander is generated using measurements.
• The use of oil free scroll expander in CHP system is considered.

The present paper focuses on the experimental characterization of an open-drive scroll expander integrated into an Organic Rankine cycle using R245fa as working fluid. The expander is a commercially available air compressor that was modified to operate in expander mode. The ORC (Organic Rankine Cycle) system is designed for a nominal heat input of 20 kW and a nominal net power output of 1.8 kW. A total of 74 steady-state operating points are measured to evaluate the expander performance over a wide range of conditions. The operating parameters that are varied include the inlet pressure (from 9 to 12 bar), outlet pressure (from 1.5 to 4 bar) and rotational speed (from 2000 to 3500 rpm). The maximum isentropic efficiency and shaft power are, respectively, 75.7% and 2.1 kW. A maximum cycle efficiency of 8.5% is reached for evaporating and condensing temperatures of 97.5 °C and 26.6 °C respectively. For most of the tests, hot water is produced in the condenser and the system therefore behaves as a CHP (combined heat and power). Depending on the water temperature requirement, a power to heat ratio varying between 1.9% and 11.8% is obtained. Water over 50 °C can be produced with a power to heat ratio higher than 8%.The experimental data points are then used to generate a performance map of the expander. This performance map allows for simulation of the use of such an expander in other ORC system.