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Session: Operational experience I
Session starts: Monday 07 October, 10:00
Presentation starts: 10:20
Room: Ruys & Rijckenvorsel Zaal

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Marco Frassinetti (Exergy)
Dario Rizzi (Exergy)
Aldo Serafino (Exergy)
Lorenzo Centemeri (Exergy)
Claudio Spadacini (Exergy)

Abstract:
All the existing ORC cycles worldwide that have been based on turbomachinery are employing axial or radial inflow turbines. Exergy has introduced a new alternative configuration: the radial outflow turbine. The radial outflow turbine has many unique characteristics which result in high ORC engines efficiency. The high efficiency of the machine is combined with the better overall cycle efficiency as a result of higher pressure ratio and volumetric ratio. In detail, Exergy radial outflow turbine most distinguishing features are: - The generally high inlet/outlet volumetric flow ratio is well combined with the change in cross section across the radius; - Compared to an axial turbine, the low inlet volumetric flow is compensated by higher blades at the first stage. This is due to the section change available along the radius, so that there is no need for partial admission; - The constant peripheral velocity along the blade span leads to constant velocity triangles and to prismatic blades; - Tip leakages and disk friction losses are minimized by the multi-stage configuration on a single disk; - The single disk/multi-stage configuration allows a solution with higher number of stages in overhung arrangement without affecting the rotordynamics of the turbine; - The intrinsic limits of a radial outflow expander to develop high enthalpy drop is not relevant for this cycle, presenting itself a very low enthalpy drop. Moreover the tip speed is limited by the low speed of sound and consequently this kind of expander suits well with this cycle arrangement. The predicted results about the radial outflow turbine presented at the 1st International Seminar on ORC Power Systems are reviewed and they are compared with empirical data from field. Firstly a brief description of the turbines is provided and the instruments used to perform the measurements are presented. Secondly the measured data are plotted, compared with the thermodynamic simulations and CFD analysis performed during the design phase. Finally an evolution of the radial outflow turbine is proposed and analyzed.