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Article

Thermodynamic Selection of the Optimal Working Fluid for Organic Rankine Cycles

1
Department of Energy Engineering, Budapest University of Technology and Economics, Muegyetem rkp. 3, H-1111 Budapest, Hungary
2
Centre for Energy Research, Department of Thermohydraulics, Hungarian Academy of Science, P.O. Box 49, H-1525 Budapest, Hungary
*
Author to whom correspondence should be addressed.
Energies 2019, 12(10), 2028; https://doi.org/10.3390/en12102028
Received: 6 May 2019 / Revised: 20 May 2019 / Accepted: 24 May 2019 / Published: 27 May 2019
A novel method proposed to choose the optimal working fluid—solely from the point of view of expansion route—for a given heat source and heat sink (characterized by a maximum and minimum temperature). The basis of this method is the novel classification of working fluids using the sequences of their characteristic points on temperature-entropy space. The most suitable existing working fluid can be selected, where an ideal adiabatic (isentropic) expansion step between a given upper and lower temperature is possible in a way, that the initial and final states are both saturated vapour states and the ideal (isentropic) expansion line runs in the superheated (dry) vapour region all along the expansion. Problems related to the presence of droplets or superheated dry steam in the final expansion state can be avoided or minimized by using the working fluid chosen with this method. Results obtained with real materials are compared with those gained with model (van der Waals) fluids; based on the results obtained with model fluids, erroneous experimental data-sets can be pinpointed. Since most of the known working fluids have optimal expansion routes at low temperatures, presently the method is most suitable to choose working fluids for cryogenic cycles, applied for example for heat recovery during LNG-regasification. Some of the materials, however, can be applied in ranges located at relatively higher temperatures, therefore the method can also be applied in some limited manner for the utilization of other low temperature heat sources (like geothermal or waste heat) as well. View Full-Text
Keywords: adiabatic expansion; isentropic expansion; T-s diagram; working fluid classification; optimization adiabatic expansion; isentropic expansion; T-s diagram; working fluid classification; optimization
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MDPI and ACS Style

Imre, A.R.; Kustán, R.; Groniewsky, A. Thermodynamic Selection of the Optimal Working Fluid for Organic Rankine Cycles. Energies 2019, 12, 2028. https://doi.org/10.3390/en12102028

AMA Style

Imre AR, Kustán R, Groniewsky A. Thermodynamic Selection of the Optimal Working Fluid for Organic Rankine Cycles. Energies. 2019; 12(10):2028. https://doi.org/10.3390/en12102028

Chicago/Turabian Style

Imre, Attila R., Réka Kustán, and Axel Groniewsky. 2019. "Thermodynamic Selection of the Optimal Working Fluid for Organic Rankine Cycles" Energies 12, no. 10: 2028. https://doi.org/10.3390/en12102028

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