AixLib.DataBase.Media.Refrigerants.HelmholtzEquationOfStateBaseDateDefinition

# .AixLib.DataBase.Media.Refrigerants.HelmholtzEquationOfStateBaseDateDefinition

Base data definition for fitting coefficients of the Helmholtz EoS

## Information

This record is a base data definition for fitting coefficients of the Helmholtz equation of state (EoS). The EoS allows the accurate description of fluids' thermodynamic behaviour and uses the Helmholtz energy as fundamental thermodynamic relation with temperature and density as independent variables. The general formula of the EoS as it is implemented within AixLib.Media.Refrigerants.Interfaces.TemplateHybridTwoPhaseMediumRecord is given below:

As it can be seen, the general formula of the EoS can be divided in two part: The ideal gas part and the residual part. Both parts' formulas are given below:

Both, the ideal gas part and the residual part can be divided in three subparts (i.e. the summations) that contain different coefficients (e.g. nL, li, pi or ei). These coefficients are the fitting coefficients and must be obtained during a fitting procedure. While the fitting procedure, the general formula of the EoS is fitted to external data (e.g. obtained from measurements or external media libraries) and the fitting coefficients are determined.

#### Assumptions and limitations

The fitting procedure is performed for a predefined range of the external data that is given in terms of, for example, temperature and pressure. Therefore, all other thermodynamic state properties are also just defined within a certain predefined range and, as a consequence, the fitting coefficients are also just valid within the predefined range of Helmholtz energy.

#### References

Thorade, Matthis; Saadat, Ali (2012): HelmholtzMedia - A fluid properties library. In: Proceedings of the 9th International Modelica Conference; September 3-5; 2012; Munich; Germany. Linköping University Electronic Press, S. 63–70.

Thorade, Matthis; Saadat, Ali (2013): Partial derivatives of thermodynamic state properties for dynamic simulation. In: Environmental earth sciences 70 (8), S. 3497–3503.

Sangi, Roozbeh; Jahangiri, Pooyan; Klasing, Freerk; Streblow, Rita; Müller, Dirk (2014): A Medium Model for the Refrigerant Propane for Fast and Accurate Dynamic Simulations. In: The 10th International Modelica Conference. Lund, Sweden, March 10-12, 2014: Linköping University Electronic Press (Linköping Electronic Conference Proceedings), S. 1271–1275

## Revisions

- June 9, 2017, by Mirko Engelpracht, Christian Vering:
  First implementation (see issue 408).

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