Package Modelica.Media.UsersGuide
User's Guide of Media Library
Information
Library Modelica.Media is a free Modelica package providing
a standardized interface to fluid media models and specific
media models based on this interface.
A fluid medium model defines algebraic equations
for the intensive thermodynamic variables used in the mass
and energy balance of component models. Optionally, additional
medium properties can be computed such as dynamic viscosity or thermal
conductivity. Medium models are defined for single and
multiple substance fluids with one and
multiple phases.
A large part of the library provides specific medium models
that can be directly utilized. This library can be used in
all types of Modelica fluid libraries that may have different connectors
and design philosophies. It is particularly utilized
in the Modelica_Fluid library (the Modelica_Fluid library is currently
under development to provide 1D therm-fluid flow components for
single and multiple substance flow with one and multiple phases).
The Modelica.Media library has the following
main features:
- Balance equations and media model equations
are decoupled.
This means that the used medium model does usually not have an
influence on how the balance equations are formulated.
For example, the same balance equations are used for media
that use pressure and temperature, or pressure and specific
enthalpy as independent variables, as well as for
incompressible and compressible media models.
A Modelica tool will have enough information to
generate as efficient code as a traditional
(coupled) definition. This feature is described in more
detail in section
Static State Selection.
- Optional variables, such as dynamic viscosity, are only computed if
needed in the corresponding component.
- The independent variables of a medium model do not
influence the definition of a fluid connector port.
Especially, the media models are implemented in such a way
that a connector may have the minimum number of independent
medium variables in a connector and still get the same
efficiency as if all medium variables are passed by the
connector from one component to the next one (the latter
approach has the restriction that a fluid port can only
connect two components and not more). Note, the Modelica_Fluid
library uses the first approach, i.e., having a set of
independent medium variables in a connector.
- The medium models are implemented with regards to
efficient dynamic simulation. For example, two phase
medium models trigger state events at phase boundaries
(because the medium variables are not differentiable
at this point).
This User's Guide has the following main parts:
- Medium usage
describes how to use a medium model from
this library in a component model.
- Medium definition
describes how a new fluid medium
model has to be implemented.
- ReleaseNotes
summarizes the changes of the library releases.
- Contact
provides information about the authors of the library as well as
acknowledgements.
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Package Contents
Information
Version included in Modelica 3.0
See top-level release notes for MSL.
Version 1.0, 2005-03-01
Many improvements in the library, e.g., providing mixtures
of the ideal gases, table based media, test suite for all media, improved and
updated User's Guide.
Version 0.9, 2004-10-18
- Changed the redeclaration/extends within packages from the
experimental feature to the language keywords introduced
in Modelica 2.1.
- Re-introduced package "Water.SaltWater" in order to test
substance mixtures (this medium model does not describe
real mixing of water and salt).
- Started to improve the documentation in
Modelica.Media.UsersGuide.MediumDefinition.BasicStructure
Version 0.792, 2003-10-28
This is the first version made available for the public
for the Modelica'2003 conference (for evaluation).
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Information
Library officer and main author
Hubertus Tummescheit
Modelon AB
Ideon Science Park
SE-22730 Lund, Sweden
email: Hubertus.Tummescheit@Modelon.se
Acknowledgements
The development of this library has been a collaborative effort
and many have contributed:
- The essential parts of the media models have been implemented
in the ThermoFluid library by Hubertus Tummescheit with
help from Jonas Eborn and Falko Jens Wagner. These media models
have been converted to the Modelica.Media interface definition
and have been improved by Hubertus Tummescheit.
- The effort for the development of the Modelica.Media library has been
organized by Martin Otter who also contributed to the design,
implemented part of the generic models, contributed to the User's Guide
and provided the generic test suite Modelica.Media.Examples.Tests.
- The basic idea for the medium model interface based on packages
is from Michael Tiller who also contributed to the design.
- The first design of the medium model interface is from
Hilding Elmqvist. The design and the implementation has been further
improved at the Modelica design meetings in
Dearborn, Nov. 20-22, 2002
Dearborn, Sept. 2-4, 2003
Lund Jan. 28-30, 2004
Munich, May 26-28, 2004
Lund, Aug. 30-31, 2004
Dearborn, Nov. 15-17, 2004
Cremona Jan. 31 - Feb. 2, 2005.
- Hans Olsson, Sven Erik Mattsson and Hilding Elmqvist developed
symbolic transformation algorithms and implemented them in Dymola
to improve the efficiency considerably (e.g., to avoid non-linear
systems of equations).
- Katrin Pröß implemented the moist air model
- Rüdiger Franke performed the first realistic tests of the Modelica.Media
and Modelica_Fluid libraries and gave valuable feedback.
- Francesco Casella has been the most relentless bug-hunter and tester of the
water and ideal gas properties. He also contributed to the User's Guide.
- John Batteh, Daniel Bouskela, Jonas Eborn, Andreas Idebrant, Charles Newman,
Gerhart Schmitz, and the users of the ThermoFluid library provided
many useful comments and feedback.
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