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Session: Session 6C: Volumetric Expanders (2)
Session starts: Wednesday 11 September, 09:00
Presentation starts: 10:00
Room: Templar's

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Fabio Fatigati (University of L'Aquila)
Marco Di Bartolomeo (University of L'Aquila)
Davide Di Battista (University of L'Aquila)
Roberto Cipollone (University of L'Aquila)

Abstract:
Volumetric expanders are the most suitable technological solution for small scale ORC power units thanks to their compactness, flexibility, capacity to manage two-phase working fluid and low operating revolution speed. Among the positive displacement expanders, sliding vane rotary expanders (SVRE) is one of the most reliable and cheaper alternative. Nevertheless, volumetric and friction losses affect their performances more than other volumetric technologies. Moreover, some design choices introduced to reduce the volumetric losses such as the increase of the number of the vanes, lead to an increase of the mechanical power losses due to viscous and friction effects. A way to improve the performances of SVRE is be represented by the dual intake port technology, which involves a further intake phase after the end of the main one. Indeed, keeping constant the mass flow rate provided by the pump, the dual intake expander produces a mechanical power close to the single intake machine with a lower intake pressure. The machine, in fact, is more permeable and this reduces, for a given flow rate imposed by the pump, the upstream pressure at the expander’s inlet. This aspect ensures the reduction of both volumetric and friction losses as they are proportional to pressure difference between consecutive vanes. Moreover, the dual intake expander operating at lower intake pressure allows to preserve the sealing components integrity, increasing reliability. This novel design option was analyzed in this paper through a 1-D CFD model, validated on a wide set of experimental data collected on an ORC-based power unit test bench. The analysis opens the way to a model based design approach which aim to develop a new technological concept of SVRE.