Volumetric and Turbine Expander Technologies in Organic Rankine Cycle Systems: A Systematic Review

The present study provides a systematic review of expander technologies used in organic Rankine cycle (ORC) systems, examining their operational principles, performance characteristics, and application domains. Expanders can be broadly categorized into turbo and volumetric types, each exhibiting distinct operational advantages. Turbo expanders exhibit high isentropic efficiency and are well suited to high-temperature, high-mass-flow conditions. Their performance strongly depends on blade geometry and operating conditions, which can be optimized through computational fluid dynamics, meanline design, and advanced features such as variable guide vanes and partial admission. Volumetric expanders—including scroll, vane, and screw expanders—are commonly adopted in small- to medium-scale systems because of their simplicity, low cost, and ability to handle two-phase fluids. Scroll expanders are most effective at power outputs below 6 kW, whereas screw expanders provide a wider operational speed range and higher adaptability. Vane expanders, while compact, suffer from efficiency limitations due to internal leakage. All volumetric expanders face technical challenges related to sealing effectiveness, frictional losses, material selection, and thermal stresses. Turbo expanders, which require high manufacturing precision, are more frequently analyzed via simulations than experiments. This review consolidates current advancements, identifies unresolved technical barriers, and outlines strategies for performance enhancement. The insights presented herein are expected to inform expander selection, support system-level design (including control strategies for variable heat sources and mechanical expander–generator coupling), and guide future research, ultimately facilitating the deployment of ORC systems in sustainable and low-grade heat recovery applications.