Package Modelica.​Media.​Water
Medium models for water

Information

This package contains different medium models for water:

• ConstantPropertyLiquidWater
  Simple liquid water medium (incompressible, constant data).
• IdealSteam
  Steam water medium as ideal gas from Media.IdealGases.SingleGases.H2O
• WaterIF97 derived models
  High precision water model according to the IAPWS/IF97 standard (liquid, steam, two phase region). Models with different independent variables are provided as well as models valid only for particular regions. The WaterIF97_ph model is valid in all regions and is the recommended one to use.

Overview of WaterIF97 derived water models

The WaterIF97 models calculate medium properties for water in the liquid, gas and two phase regions according to the IAPWS/IF97 standard, i.e., the accepted industrial standard and best compromise between accuracy and computation time. It has been part of the ThermoFluid Modelica library and been extended, reorganized and documented to become part of the Modelica Standard library.

An important feature that distinguishes this implementation of the IF97 steam property standard is that this implementation has been explicitly designed to work well in dynamic simulations. Computational performance has been of high importance. This means that there often exist several ways to get the same result from different functions if one of the functions is called often but can be optimized for that purpose.

Three variable pairs can be the independent variables of the model:

1. Pressure p and specific enthalpy h are the most natural choice for general applications. This is the recommended choice for most general purpose applications, in particular for power plants.
2. Pressure p and temperature T are the most natural choice for applications where water is always in the same phase, both for liquid water and steam.
3. Density d and temperature T are explicit variables of the Helmholtz function in the near-critical region and can be the best choice for applications with super-critical or near-critical states.

The following quantities are always computed in Medium.BaseProperties:

In some cases additional medium properties are needed. A component that needs these optional properties has to call one of the following functions:

More details are given in Modelica.Media.UsersGuide.MediumUsage.OptionalProperties. Many additional optional functions are defined to compute properties of saturated media, either liquid (bubble point) or vapour (dew point). The argument to such functions is a SaturationProperties record, which can be set starting from either the saturation pressure or the saturation temperature. With reference to a model defining a pressure p, a temperature T, and a SaturationProperties record sat, the following functions are provided:

Details on usage and some examples are given in: Modelica.Media.UsersGuide.MediumUsage.TwoPhase.

Many further properties can be computed. Using the well-known Bridgman's Tables, all first partial derivatives of the standard thermodynamic variables can be computed easily.

The documentation of the IAPWS/IF97 steam properties can be freely distributed with computer implementations and are included here (in directory Modelica/Resources/Documentation/Media/Water/IF97documentation):

• IF97.pdf The standards document for the main part of the IF97.
• Back3.pdf The backwards equations for region 3.
• crits.pdf The critical point data.
• meltsub.pdf The melting- and sublimation line formulation (not implemented)
• surf.pdf The surface tension standard definition
• thcond.pdf The thermal conductivity standard definition
• visc.pdf The viscosity standard definition

Extends from Modelica.​Icons.​VariantsPackage (Icon for package containing variants).

Package Contents

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