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Energies 2014, 7(9), 5548-5565; doi:10.3390/en7095548

Performance of Siloxane Mixtures in a High-Temperature Organic Rankine Cycle Considering the Heat Transfer Characteristics during Evaporation

Lehrstuhl für Technische Thermodynamik und Transportprozesse, Zentrum für Energietechnik, Universität Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany
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Received: 30 June 2014 / Revised: 5 August 2014 / Accepted: 18 August 2014 / Published: 26 August 2014
(This article belongs to the Special Issue Waste Heat Recovery—Strategy and Practice)
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Abstract

The application of the Organic Rankine Cycle to high temperature heat sources is investigated on the case study of waste heat recovery from a selected biogas plant. Two different modes of operation are distinguished: pure electric power and combined heat and power generation. The siloxanes hexamethyldisiloxane (MM) and octamethyltrisiloxane (MDM) are chosen as working fluids. Moreover, the effect of using mixtures of these components is analysed. Regarding pure electricity generation, process simulations using the simulation tool Aspen Plus show an increase in second law efficiency of 1.3% in case of 97/03 wt % MM/MDM-mixture, whereas for the combined heat and power mode a 60/40 wt % MM/MDM-mixture yields the highest efficiency with an increase of nearly 3% compared to most efficient pure fluid. Next to thermodynamic analysis, measurements of heat transfer coefficients of these siloxanes as well as their mixtures are conducted and Kandlikar’s correlation is chosen to describe the results. Based on that, heat exchanger areas for preheater and evaporator are calculated in order to check whether the poorer heat transfer characteristics of mixtures devalue their efficiency benefit due to increased heat transfer areas. Results show higher heat transfer areas of 0.9% and 14%, respectively, compared to MM. View Full-Text
Keywords: Organic Rankine Cycle; siloxanes; high temperature heat source; zeotropic mixtures; heat transfer coefficients; heat exchange area Organic Rankine Cycle; siloxanes; high temperature heat source; zeotropic mixtures; heat transfer coefficients; heat exchange area
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This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Weith, T.; Heberle, F.; Preißinger, M.; Brüggemann, D. Performance of Siloxane Mixtures in a High-Temperature Organic Rankine Cycle Considering the Heat Transfer Characteristics during Evaporation. Energies 2014, 7, 5548-5565.

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