Effects of specifying thermodynamic method overrides

In the Fluid Editor, you can override the system thermodynamic method for certain property calculations. Currently, you can override the thermodynamic method for the following properties:

• Vapor Enthalpy

• Liquid Enthalpy

• Liquid Density

  

When you set one of these method-override options to a value other than the System thermodynamic method, the software calculates the property value according to the selected thermodynamic method and overrides the property value calculated during the equilibrium calculations. These overrides apply only after the equilibrium calculations are complete and do not affect the properties calculated and used in the equilibrium calculations. This effect is important for the Poynting correction and Henry's Law pressure correction that you can apply for some Fluid Types.

If your Fluid Type includes the Poynting correction (the Use Poynting Correction checkbox is selected) or the Henry's Law pressure correction (the Apply Henry's Law Pressure Correction using Brelvi O'Connell Model checkbox is selected), the Poynting correction and Henry's Law pressure correction always use the pure component volume data calculated from the temperature-dependent property correlations for liquid density, regardless of the Liquid Density selection in your Fluid Type. The temperature-dependent property correlations are defined by the pure component (PURECOMP) data bank that the Fluid Type uses and by the local thermodynamic data overrides specified on the Temperature Dependent tab in the Component Data section of the Fluid Editor.

Most streams include a PhaseProp submodel from the Submodels Library. (The Submodels Library appears only for Model Writers.) The PhaseProp submodel displays extended property values for the stream based on the stream configuration, including the liquid density for each component in the fluid. However, the liquid density in the PhaseProp submodel always displays the liquid density calculated from the temperature-dependent property correlations for liquid density, regardless of the Liquid Density selection in your Fluid Type. Therefore, if the Liquid Density option in the corresponding Fluid Type is not set to the System thermodynamic method, then the liquid density of the mixture that you see in the fluid may not match the hand-calculated value based on the pure component liquid densities in the PhaseProp submodel.