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Session: Parallel Session: Small-capacity systems
Session starts: Friday 23 September, 14:00
Presentation starts: 14:00
Room: Auditorium

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Antti Uusitalo ()
Juha Honkatukia ()
Teemu Turunen-Saaresti ()
Jaakko Larjola ()
Piero Colonna ()

Abstract:
ABSTRACT Most of the Organic Rankine Cycle (ORC) power systems currently on the market features an electrical power output in the range 100 kWe – 5 MWe. However, there are many energy conversion applications where an ORC energy converter with an electrical power capacity of ca. 10 kWe is attractive. Examples are heat recovery from prime movers, concentrated solar power, small-scale cogeneration of heat and power (e.g. for domestic use). In all these applications the thermal source is at moderate or high temperature. One of the key issues in designing a small-scale ORC turbogenerator is the selection of a suitable working fluid. Siloxanes have been successfully adopted in high-temperature ORC power plants for larger power capacities (400 kWe – 2 MWe). The main focus of this study is the evaluation of eight siloxanes as working fluid for a small-capacity ORC turbogenerator based on a high-speed technology. High-speed technology refers to the concept of a compact hermetic component containing the turbine, the generator, and the feed pump coupled to the same shaft, rotating at high speed (typically more than 20 000 rpm) and using the working fluid in the liquid phase to lubricate the shaft bearings. The siloxanes considered in the study are D4, D5, D6, MM, MDM, MD2M, MD3M, and MD4M. Toluene is included in the analysis as a reference working fluid. The effects of adopting different siloxanes on the thermodynamic cycle configuration, conversion efficiency, and on the turbine and component design are studied by means of computations. The working fluid parameters which are most influential are the critical temperature and pressure, and the molecular complexity, and, related to them, the condensation pressure, density and specific enthalpy over the expansion which affects the optimal design of the turbine. The fluid thermal stability is also extremely relevant in the considered applications. The results of this study provide valuable information for the design of efficient ORC systems in the tens-of-kW power range utilizing siloxanes as working fluids. Further research will be centered on technological issues, such as material requirements, process component design, as well as safety and reliability issues. REFERENCES [1] J.P. van Buijtenen, J. Larjola, T. Turunen-Saaresti, J. Honkatukia, H. Esa, J. Backman and A. Reunanen: “Design and validation of a new high expansion ratio radial turbine for ORC application” 5th European conference on Turbomachinery, Prague, March 17-22, 2003 [2] P. Colonna, N. R. Nannan, A. Guardone, “Multiparameter equations of state for siloxanes: [(CH3)3-Si-O1/2]2-[O-Si-(CH3)2]i=1,...,3, and [O-Si-(CH3)2]6”, Fluid Phase Equilibria vol. 263, no. 2, pp. 115–130, 2008.