A Review on Two-Phase Volumetric Expanders and Their Applications

Abstract

The importance of volumetric expanders has been increasing in the last decades because several studies confirmed that they lead to improved energy savings, limit the environmental impact, and reduce the energy intensity of industrial and domestic applications. In particular, several applications of the two-phase volumetric expanders, in which the operating fluid consists of liquid and vapor phases, were recently proposed. Nevertheless, the contributions in the scientific literature related to the overview of the state-of-the-art aspects of this technology are rare. For this reason, the present work discussed the potentialities and drawbacks of the available typologies of volumetric expanders that process a two-phase pure working fluid by analyzing a summary of leading studies in this field to go beyond previous efforts in the literature. The analysis revealed that twin-screw machines represent the best candidates, while reciprocating piston devices seemed the least well-adapted because of their reduced tolerance to droplets and high friction losses. Flash evaporation appeared to have the most significant impact on the expander because it affects both inlet and expansion phases, thus, determining the shape of the indicated cycle and the isentropic efficiency.