Review of Key Features of Selected Fluid Machines for Energy Systems

Fluid machines like compressors and expanders handling vapor or two-phase flows are required in many energy systems. Using a historical perspective the paper aims at highlighting key features of common technologies like scroll and twin-screw among the volumetric family and radial or axial among the dynamic family. One example of mechanical vapor recompression is cited to illustrate how some of the features considered can help practical decision making when operation deviate from expected nominal conditions. Another example highlights the importance of thermodynamic disequilibrium on the expected performance of two-phase expanders for geothermal fluids or heat pump cycles. Other examples relate to the oil-fluid mixtures in machines, particularly in the case two-stage heat pump cycles. Finally, the difficult path towards oil-free machines in small to medium scale machines is mentioned. At a time where AI design approaches for machines are anticipated this contribution could help overcoming some of the vital elements of choice for engineers.