Mapping of the temperature-entropy diagrams of van der Waals fluids

Attila R. Imre, Réka Kustán, Axel Groniewsky

Research output: Contribution to journalArticle


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 T-s diagrams of working fluids can be understood.

Original languageEnglish
Article number1519
Issue number6
Publication statusPublished - Mar 2020


  • Adiabatic expansion
  • Molecular degree of freedom
  • T-s diagram
  • Working fluid classification

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Energy Engineering and Power Technology
  • Energy (miscellaneous)
  • Control and Optimization
  • Electrical and Electronic Engineering

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