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Session: Poster session & Sponsor Exhibition
Session starts: Monday 07 October, 14:00

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George Kosmadakis (Agricultural University of Athens)
Dimitris Manolakos (Agricultural University of Athens)
Erika Ntavou (Agricultural University of Athens)
George Papadakis (Agricultural University of Athens)

Abstract:
A subcritical solar two-stage organic Rankine cycle (ORC) has been designed, according to optimization studies that have been conducted [1], and then manufactured. Some of its components have been properly modified (e.g. scroll compressors in reverse operation) in order to operate efficiently, while all components have been placed in a test-rig, equipped with the appropriate measuring equipment for its detailed experimental testing. An important feature of this ORC engine, with a capacity of around 10 kW and an efficiency of 10%, is the use of two similar scroll expanders, placed in series. The reason for selecting such configuration emanates from the requirement to operate these expansion machines at high efficiency (even over 70%). In other words, to keep the pressure ratio close to their built-in value, approximately equal to 3. The total pressure ratio at maximum heat input (maximum heat input: 100 kWth at around 130 oC) with a condensation temperature of 30 oC is close to 9-10, using the organic fluid R-245fa. At such conditions both expanders operate with high expansion efficiency, while at lower heat input when the evaporation temperature/pressure is lower, the first expander is totally by-passed and only the second one operates. By doing so, for the whole heat input range the scroll expanders operate at high efficiency and close to their maximum value, significantly contributing to a high system performance. The experimental testing of such ORC engine includes the controlled heat input from an electric heater (resembling the operation of a solar field), while focus is given on some operating parameters, such as the organic fluid mass flow rate, the rotational speeds of the expansion machines and the pump and the appropriate timing of by-passing the first expander. Acknowledgement: The present work is conducted within the framework of the project with contract No. 09SYN-32-982, partly funded by the Greek General Secretary of Research and Technology (GSRT). REFERENCES [1] G. Kosmadakis, D. Manolakos, G. Papadakis, “Investigating the double-stage expansion in a solar ORC”, Presented in the 1st Int Seminar on ORC Power Systems (ORC2011), Delft, The Netherlands, 22-23 September 2011.