Modelica Fluid was announced together with Modelica.Media on the Modelica’2003 conference, after the Modelica Association had made an attempt to standardize the most important interfaces and to provide good solutions for the basic problems of fluid modeling. By now Modelica.Media is widely used; regarding Modelica Fluid it has not been possible to utilize 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.

Exploiting lessons learned the Modelica Associaton 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 a flow, such as specific enthalpy transported by a mass flow. This makes it possible that the significant amount of work that went into Modelica_Fluid finally yields fruits (17 persons have contributed to the development 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 have been decoupled from the device models based on them. This not only simplifies the readability and understanding, but also the maintenance and further development of the library.

Take the simple model of a heating system shown in the figure as example: as simple as it is, it features steady-state simulation and dynamic simulation with fixed or steady-state initial conditions by just changing one configuration parameter in the global system object. It treats a closed flow cycle in each of these settings; it contains an idealized pressure control embedded in the pump as well as a simple temperature control in the burner. The heater, the pipe and the radiator have detailed pressure loss models covering small laminar and zero flow as well, depending on the valve opening.

Modelica Fluid 1.0 has been released on January 28, 2009, and can be downloaded here.

Partial financial support of ABB and DLR by BMBF (BMBF Förderkennzeichen: 01IS07022F) for the further development of Modelica_Fluid within the ITEA project EUROSYSLIB is highly appreciated.

This article is provided by Rüdiger Franke (ABB) and Francesco Casella (Politecnico di Milano).