Experimental modeling of a lubricated, open drive scroll expander for micro-scale organic Rankine cycle systems

Scroll compressors converted into expanders represent a good choice in micro-to-small-scale organic Rankine cycle (ORC) applications. Several studies have tested and modeled scroll expanders in ORC systems in the last decade to assess their performance and reliability in off-design conditions. In this work, SANDEN TRS090F scroll compressor is converted into an expander and tested in a micro-scale ORC system using R134a for power generation from low-grade heat. The experimental data are used to modify the available semi-empirical model in the literature considering a polytropic expansion, a more detailed suction pressure drop model, and a variable loss power correlated to the expander pressure ratio. In addition, the two known expander geometrical parameters, the built-in volume ratio, and the swept volume are considered as fixed inputs to the model instead of being determined as part of the model results. In general, the results of the analysis show that the proposed model can predict the expander's overall performance with good accuracy in different operating conditions. The maximum deviation between the model results and most of the measurements is 5% for the mass flow rate and the shaft power, 15% for the overall isentropic efficiency, and 3 K for the discharge temperature. Then, the impact of the different losses is presented, and finally, the validated model is used to generate the performance maps of the studied expander at different working conditions.