The Riemann problem for a van der Waals fluid with entropy rate admissibility criterion — Isothermal case

1986 ◽  
Vol 92 (3) ◽  
pp. 247-263 ◽  
Author(s):  
Harumi Hattori
Keyword(s):  
Riemann Problem ◽  
Van Der Waals ◽  
Entropy Rate ◽  
Van Der Waals Fluid ◽  
Isothermal Case

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

Energies ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1519 ◽  
Author(s):  
Attila Imre ◽  
Réka Kustán ◽  
Axel Groniewsky
Keyword(s):  
Van Der Waals ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Model Material ◽  
Qualitative Description ◽  
Working Fluid ◽  
Expansion Phase ◽  
Van Der Waals Fluid ◽  
Characteristic Points ◽  
Reduced Temperature

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 T–s diagrams of working fluids can be understood.

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