The ExternalMedia project was started in 2006 by Francesco Casella and Christoph Richter, with the aim of providing a framework for interfacing external codes computing fluid properties to Modelica.Media-compatible component models. The two main requirements were: maximizing the efficiency of the code and minimizing the amount of extra code required to use your own external code within the framework. The library was described in this paper.
The first implementation featured a hidden cache in the C++ layer and used integer unique IDs to reference that cache. This architecture worked well if the models did not contain implicit algebraic equations involving medium properties, but had serious issues when such equations were involved, which is often the case when solving steady-state initialization problems. The library was shipped with an interface to the FluidProp software, provided at the time by TU Delft.
The library was then restructured in 2012 by Francesco Casella and Roberto Bonifetto. The main idea was to get rid of the hidden cache and of the unique ID references and use the Modelica state records instead for caching. In this way, all optimizations performed by Modelica tools are guaranteed to give correct results, also in case of implicit equations, which was previously not the case. The library was mainly used with the Dymola tool, although some limited support for OpenModelica was given.
In 2013, the open-source CoolProp package was integrated in the library, thus providing built-in access to a wide range of fluids.
In 2014, Ian Bell initially provided some makefiles to automatically compile different versions of the library. Later on, Jorrit Wronski added support for CMake scripts.
In 2021, Jorrit Wronksi implemented the entire CMake build pipeline within the GitHub CI environment. New annotations introduced in Modelica 3.4 now allow to build and ship the ExternalMedia package with built-in pre-compiled libraries for many different operating systems, C-compilers, and Modelica tools.
In 2023, Federico Terraneo helped switching from statically linked to dynamically linked compiled binaries, while keeping access to the ModelicaError function to properly handle run-time and compile time errors generated by external media models. This eliminates the need to have different binaries for each compiler, now only one DLL/shared library is needed for each operating system. At long last, ExternalMedia can be used out of the box with different Modelica tools and operating systems, without the need of arcane installation procedures.