Experimental and numerical optimization of a scroll expander for small-scale ORC systems using pure and mixture working fluids

This study presents a comprehensive investigation into scroll expander optimization for small-scale organic Rankine cycle (ORC) systems through combined experimental and numerical approaches. A systematic evaluation is conducted on five working fluids (including two pure working fluids and three mixture working fluid) to quantify their thermodynamic impacts on expander performance. A small-scale ORC test rig is engineered to characterize operational behavior and provide experimental boundary conditions for numerical validation. A three-dimensional transient computational fluid dynamics model incorporating real gas equations of state is developed, enabling precise analysis of pressure-rotation coupling effects on output power and isentropic efficiency. This study further establish response surface methodology (RSM) using Box-Behnken design to derive multi-objective optimization frameworks, identifying optimal operating parameters that maximize both output power and isentropic efficiency. Results indicate that the output power keep rising with inlet pressure, whereas the isentropic efficiency initially increases and then decreases with inlet pressure. R245fa exhibits a maximum isentropic efficiency of 49.2 %, representing a 6.91 % higher than 0.3R123/0.7R245fa (45.8 %). The predicted output power of the scroll expander ranges from 1.949 to 2.43 kW, reaching a maximum of 2.43 kW for 0.3R123/0.7R245fa, which is 17.8 % higher than that of pure working fluids. The minimum error between the predicted and simulated values of isentropic efficiency is 1.28 %. The findings of this study provide valuable guidance for the design and manufacturing of high-efficiency scroll expanders tailored for small-scale ORC applications.