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Open AccessArticle

Mapping of the Temperature–Entropy Diagrams of van der Waals Fluids

1
Department of Energy Engineering, Faculty of Mechanical Engineering, Budapest University of Technology and Economics, Műegyetem rkp. 3, H-1111 Budapest, Hungary
2
Department of Thermohydraulics, Centre for Energy Research, POB. 49, H-1525 Budapest, Hungary
*
Author to whom correspondence should be addressed.
Energies 2020, 13(6), 1519; https://doi.org/10.3390/en13061519
Received: 14 February 2020 / Revised: 13 March 2020 / Accepted: 16 March 2020 / Published: 23 March 2020
The shape of the temperature vs. specific entropy diagram of a working fluid is very important to understanding the behavior of fluid during the expansion phase of the organic Rankine cycle or similar processes. Traditional wet-dry-isentropic classifications of these materials are not sufficient; several materials remain unclassified or misclassified, while materials listed in the same class might show crucial differences. A novel classification, based on the characteristic points of the T–s diagrams was introduced recently, listing eight different classes. In this paper, we present a map of these classes for a model material, namely, the van der Waals fluid in reduced temperature (i.e., reduced molecular degree of freedom) space; the latter quantity is related to the molar isochoric specific heat. Although van der Waals fluid cannot be used to predict material properties quantitatively, the model gives a very good and proper qualitative description. Using this map, some peculiarities related to Ts diagrams of working fluids can be understood. View Full-Text
Keywords: adiabatic expansion; Ts diagram; working fluid classification; molecular degree of freedom adiabatic expansion; Ts diagram; working fluid classification; molecular degree of freedom
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Imre, A.R.; Kustán, R.; Groniewsky, A. Mapping of the Temperature–Entropy Diagrams of van der Waals Fluids. Energies 2020, 13, 1519.

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