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

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Markus Preißinger (Universität Bayreuth, Zentrum für Energietechnik, Lehrstuhl für Technische Thermodynamik und Transportprozesse)
Theresa Weith (Universität Bayreuth, Zentrum für Energietechnik, Lehrstuhl für Technische Thermodynamik und Transportprozesse)
Florian Heberle (Universität Bayreuth, Zentrum für Energietechnik, Lehrstuhl für Technische Thermodynamik und Transportprozesse)
Dieter Brüggemann (Universität Bayreuth, Zentrum für Energietechnik, Lehrstuhl für Technische Thermodynamik und Transportprozesse)

Abstract:
The Organic Rankine Cycle (ORC) is a widespread technology for geothermal applications and biomass fired power plants [1,2]. Due to challenging boundary conditions, like fluctuating heat transfer rates and a broad heat source temperature range, ORC units for waste heat recovery are still rare. Therefore, the adjustment of the ORC unit to the heat source is realized by choosing different working fluids and/or adapting the working pressure of the process. However, by changing the fluid, safety issues, plant specific aspects and thermodynamic conditions can change dramatically, especially when the new working fluid corresponds to a different chemical class [3]. From that point of view, the behavior of chemical classes instead of single working fluids is of great interest. In this study, homologous series of alkanes, alkylbenzenes and siloxanes are investigated for heat source temperatures of 300 °C to 600 °C. Firstly, the heat source temperature is varied and the influence of the working pressure on the exergetic efficiency is regarded for each fluid and temperature step. Secondly, the maximum exergetic efficiency and the corresponding fluid are determined from the gained results for each chemical class and temperature step. From these data a correlation for the maximum exergetic efficiency depending on the heat source temperature can be educed. For the homologous series n-pentane (C5) to n-undecane (C11) a polynomial dependency is found which predicts the maximum exergetic efficiency with a relative deviation of less than 2 % for the whole temperature range. Due to the location of the pinch-point at the beginning of the preheater, net power output depends linearly on the heat source temperature. However, pressure ratio in the turbine shows a polynomial dependency on the number of C-atoms. Additionally, main correlations for further thermodynamic and constructional parameters are deduced from simulation results and expressed by known physico-chemical input parameters (e.g. critical temperature, pressure and volume) or boundary conditions (e.g. heat source temperature). The prediction accuracy is better than 5 % for all investigated parameters. In summary, the above mentioned results are a first step towards a fluid-to-fluid modeling technique and, therefore, modular designed ORC power plants for the benefit of reduced simulation efforts for further scientific and industrial investigations.