.BrineProp.PartialBrineMultiSaltMultiGasTwoPhase

Information

• PartialBrine_ngas_Newton is based on PartialMixtureTwoPhaseMedium, an extension to the Modelica.Media library. This extension was necessary because Modelica.Media supports mixtures and two-phase media, but not both combined.
• The vapour-liquid-equilibrium (VLE) is defined by the water vapour pressure and the gas solubilites. It is determined using Newton's method.
• Explicit material functions are not specified in this package, as it is just a template. They need to be provided in the instantiating package (e.g. BrineProp.Brine_5salts_TwoPhase_3gas).
• The model calculates properties for a thermodynamic state specified by p and T, p and h, T and d or p and d.

Fluid model assumptions

• The fluid consists of water, N_s salts and N_g gases.
• Its total composition is given by a vector of mass fractions X.
• There are one or two phases: liquid and, if absolute pressure is low enough, gas (no solid phase).
• The gas phase is an ideal mixture of water vapour and gases.
• The salts are completely dissolved in and limited to the liquid phase (no precipitation/evaporation).
• Water and gases are exchanged between both phases by degassing/dissolution or evaporation/condensation, taking into account mass and energy conservation.
• Gases dissolve in liquid depending on their respective solubility, which depends on temperature and salt content, but not on the content of other gases.
• The saturation pressure of water is reduced by the salt content.
• Water evaporation and condensation depend on its saturation pressure, which depends on temperature and the salt content according to Raoult's law.
• In two-phase state degassing pressures equal the respective partial pressures.
• Both phases are assumed to be in thermodynamic equilibrium, i.e. they have the same pressure and temperature. The vapour-liquid equilibrium is instantly reached.
• Boundary surface enthalpies are neglected.

See PhD thesis for more details.

Details

Brine is a mixture of components and, if gases are involved, potentially has two phases. As this is not possible with the components provided in Modelica.Media a new Medium template had to be created by merging Modelica.Media.Interfaces.PartialMixtureMedium and Modelica.Media.Interfaces.PartialTwoPhaseMedium of the Modelica Standard Library 3.1.

The model is explicit for p and T, but for h(p,T) the inverse function T(p,h) is defined. T(p,h) is inverts h(p,T) numerically by bisection, stopping at a given tolerance.

In order to calculate h(p,T), the vapour-liquid-equilibrium (VLE) is determined, i.e. the gas mass fraction q and the compositions of the liquid phases X_l. Only h is returned, due to the limitation of DYMOLA/Modelica not allowing inverse functions of functions that are returning an array. As x (gas mass fraction) and X_l (composition of liquid phase) are of interest themselves and required to calculate density and viscosity, the VLE calculation is conducted one more time, this time with T known. This additiona unnecessary calculation doubles the workload when p,h are given. When p,T are given, however, it adds only one more calculation to the multiple iterations of the bisection algorithm.

Usage

This is a partial medium and cannot be used as is.

See BrineProp.Examples.BrineProps2phase for usage example.

See BrineProp.Examples.BrineProps2phase or info of BrineProp.Brine_5salts_TwoPhase_3gas for more usage examples.

TODO:

Known Issues:

• The package is in one file, because it extends a MSL package (DYMOLA limitiation?).

Created by

francke@gfz-potsdam.de

Contents

Revisions