Organic Rankine Cycle
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Publication Name: FLUID-DYNAMICS OF THE ORC RADIAL OUTFLOW TURBINE
Original File Name Searched: 118.pdf
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Paper ID: 118, Page 1 FLUID-DYNAMICS OF THE ORC RADIAL OUTFLOW TURBINE
Claudio Spadacini*, Lorenzo Centemeri, Dario Rizzi, Massimiliano Sanvito and Aldo Serafino
Via Santa Rita 14, 21057, Olgiate Olona (VA) Italy
Web page: http://www.exergy-orc.com
It is well documented that axial turbines and radial inflow turbines have traditionally been the selected solutions for ORC, both with an overhung configuration. In the last years a different turbine technology for ORC has been developed, engineered, manufactured and tested by Exergy: the radial outflow turbine.
In order to better understand its potential and limits, the present study has the purpose of conducting a fluid-dynamic study of the ORC radial outflow turbine. To pursue this aim, here firstly a summary description of the radial outflow turbine and of its features is given, by means of mechanical and thermodynamic fundamentals.
Secondly, moving from the hypothesis of direct coupling with generator, boundary conditions for a 2 MW case are chosen and a radial outflow turbine is studied, focusing on fluid-dynamic design: after a preliminary mean line study a CFD simulation of the machine is performed.
The described analysis includes also a comparison with an axial ORC turbine with the overhung configuration directed coupled with a generator: this approach could allow to valuate fluid-dynamic losses in both technologies and can explain the reason why the radial outflow turbine shows a higher efficiency than the axial overhung one in many ORC applications.
In these days the ORC market is in expansion and as a matter of fact a rising interest about it can be observed in the scientific community. In terms of system performance, turbine is the most important and critical component of ORC systems (Macchi, 2013) and for this reason it is subject to many researches and studies.
An interesting innovation in this panorama is the ORC radial outflow turbine developed by Exergy, which has several unique characteristics qualifying this unconventional configuration as advantageous for many ORC applications, as it ideally matches the process conditions typical for these kinds of uses. In fact it has been demonstrated (Macchi, 2013 – Frassinetti et al., 2013) that this machine is competitive with both axial and radial inflow turbines, solutions usually adopted in ORC applications with the overhung configuration as it allows to have compact machines and to reduce sealing problems (Salucci et. al, 1983).
2. THE ORC RADIAL OUTFLOW TURBINE AT A GLANCE
To better understand the particular features of the radial outflow turbine (see Figure 1) some considerations about turbomachinery fluid-dynamics and about thermodynamics are necessary.
The well-known general Euler equation for turbomachinery, ignoring minor negligible losses, provides a formulation of the specific work for a single stage as (for instance Stodola, 1927):
𝒍=𝒖𝟏 𝒄𝒕𝟏 − 𝒖𝟐 𝒄𝒕𝟐 (1)
3rd International Seminar on ORC Power Systems, October 12-14, 2015, Brussels, Belgium
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