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

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Giampaolo Manfrida (University of Florence - Department of Industrial Engineering)
Daniele Fiaschi (University of Florence - Department of Industrial Engineering)
Francesco Maraschiello (University of Florence - Department of Industrial Engineering)
Duccio Tempesti (University of Florence - Department of Industrial Engineering)

Abstract:
Organic Rankine Power Cycles (ORC) are well proven and reliable technology for energy conversion, particularly for exploiting low-temperature heat source. Nowadays, ORCs are increasing in popularity with several manufacturers of equipment available on the market. A lot of research has been dedicated to this subject, either on the heat source or on the system design and analysis, either on the criteria for selection of optimal working fluid or on the design of the expander (scroll, screw, micro-turbine, etc.) [1-3] In this paper, a micro combined heat and power (CHP) plant operating through an Organic Rankine Cycle (ORC) using geothermal energy at low temperature (80-100°C) and solar energy is presented. The system is designed to produce 50 kWe with a single turbine, while the solar field is composed only by evacuated solar collectors. The CHP plant is designed using meteorological data for a city in the centre of Italy and it is optimized in terms of cycle efficiency by varying the upper cycle pressure. Starting from the results of the energy analysis of the CHP-ORC system, a preliminary step by step design of a radial micro-turbine is carried out. The main innovative features of proposed design are the use of real fluid properties instead of ideal gases, and the estimation of turbine losses [4-7]. Six different fluids suitable for low-temperature energy conversion are investigated: R134a, R236fa, R245fa, R1234yf, n-pentane, cyclohexane. All the calculations are carried out with Engineering Equation Solver (EES®). The results show that the system can reach interesting first law efficiency (17% with cyclohexane and 15% with R245fa). Concerning the design of the turbine, for all the working fluids values of turbine efficiency within 0.78 and 0.85 are obtained, with R134a showing the maximum value (0.85). In addition, all the fluids present the same distribution of turbine losses, with friction and secondary flow losses accounting for approximately 70% of all the losses. REFERENCES [1] Schuster A, Karellas S, Kakaras E, Spliethoff H. Energetic and economic investigation of Organic Rankine Cycle applications. Applied Thermal Engineering 2009;29:1809–1817 [2] Heberle F, Brüggemann D. Exergy based fluid selection for a geothermal Organic Rankine Cycle for combined heat and power generation. Applied Thermal Engineering 2006;30: 1326-1332 [3] Tchanche BF, Lambrinos Gr, Frangoudakis A, Papadakis G. Low-grade heat conversion into power using organic Rankine cycles – A review of various applications. 2011;15:3963-3979 [4] Dixon S.L.,” Fluid Mechanics and Thermodynamics of Turbomachinery”, 1998; Butterworth, New York. [5] Whitfield A., Baines N.C.,”Design of radial turbomachines”, 1990; Longman, New York [6] Whitfield, A., “The Preliminary Design of Radial Inflow Turbines”, ASME J. of Turbomachinery, 1990;112:51-57. [7] Benson S. Rowland. " A Review of Methods For Assessing Loss Coefficients In Radial Gas Turbines". Int. J. mech. Sci. Pergamon Press. 1970;12:905-932. ACKNOWLEDGMENT The results here presented have been obtained within the framework of the project BT GEO H&P, funded by Regione Toscana, using European Social Fund (FSE) resources.