Standardization of Thermo-Fluid Modeling in Modelica.Fluid Page: 1 of 10
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Standardization of Thermo-Fluid Modeling in Modelica.Fluid
Rudiger Franke, ABB AG, Germany - Ruediger.Franke@de.abb.com,
Francesco Casella, Politecnico di Milano, Italy - Casella@elet.polimi.it,
Michael Sielemann, DLR Institute for Robotics and Mechatronics - Michael.Sielemann@dlr.de,
Katrin Proelss, TU Hamburg-Harburg, Germany - K.Proelss@tu-harburg.de,
Martin Otter, DLR Institute for Robotics and Mechatronics, Germany - Martin.Otter@dlr.de,
Michael Wetter, LBNL, USA - MWetter@lbl.gov
This article discusses the Modelica.Fluid library that
has been included in the Modelica Standard Library
3.1. Modelica.Fluid provides interfaces and basic
components for the device-oriented modeling of one-
dimensional thermo-fluid flow in networks contain-
ing vessels, pipes, fluid machines, valves and fit-
A unique feature of Modelica.Fluid is that the com-
ponent equations and the media models as well as
pressure loss and heat transfer correlations are de-
coupled from each other. All components are imple-
mented such that they can be used for media from
the Modelica.Media library. This means that an in-
compressible or compressible medium, a single or a
multiple substance medium with one or more phases
might be used with one and the same model as long
as the modeling assumptions made hold. Further-
more, trace substances are supported.
Modeling assumptions can be configured globally in
an outer System object. This covers in particular the
initialization, uni- or bi-directional flow, and dy-
namic or steady-state formulation of mass, energy,
and momentum balance. All assumptions can be lo-
cally refined for every component.
While Modelica.Fluid contains a reasonable set of
component models, the goal of the library is not to
provide a comprehensive set of models, but rather to
provide interfaces and best practices for the treat-
ment of issues such as connector design and imple-
mentation of energy, mass and momentum balances.
Applications from various domains are presented.
Keywords: Modelica, thermo-fluid; one dimensional
fluid flow, single substance, multi substance, trace
Modelica.Fluid was announced together with Mode-
lica Media at the Modelica'2003 conference, after
the Modelica Association had made an attempt to
standardize the most important interfaces and to pro-
vide good solutions for the basic problems of fluid
modeling . By now Modelica.Media is widely
used. Regarding Modelica.Fluid it has not been pos-
sible to meet the ambitious goal for device-oriented
modeling in realistic fluid applications so far. Still
many different fluid libraries exist, each defining its
own basics and each having its own downsides.
Based on lessons learned, the Modelica Association
has made a second attempt to standardize the basic
fluid interfaces during the last year. It turned out that
the regular Modelica connection approach with effort
and flow variables is not sufficient for device-
oriented fluid modeling. The newly introduced
stream variables  represent properties transported
by large-scale motion of a flow, such as specific en-
thalpy transported via convection by a mass flow.
This makes it possible that the significant amount
work that went into Modelica.Fluid finally yields
fruits; 17 persons have contributed to the develop-
ment during the last 6 years. Compared to previous
beta releases, the code was reorganized and extended
to cover the whole range from steady-state models to
dynamic energy, mass and momentum balances. The
fundamental balance equations for one-dimensional
fluid flow and heat flow have been decoupled from
the device models based on them. This not only sim-
plifies the readability and understanding, but also the
maintenance and further development of the library.
2 Library Structure and Interfaces
2.1 Library Structure
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Franke, Rudiger; Casella, Francesco; Sielemann, Michael; Proelss, Katrin; Otter, Martin & Wetter, Michael. Standardization of Thermo-Fluid Modeling in Modelica.Fluid, article, September 1, 2009; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc1013828/m1/1/: accessed February 21, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.