MultiPhaseMixture has an interface to the C-interface ExternalMultiPhaseMixture which makes it possible to use fluids from an external property package. The overall structure of the framework can be seen below.

Using a external fluid in Modelica

To use a fluid from an external property package:

Challenges with external property code

Most of the available external property packages have not been designed to be used for dynamic simulations. General problems are:

We have seen in this project that without any additional handling of the validity region issue, simulation will often crash during initialization or simulation. An explanation is that even if a simulation model is set-up to operate within the validity region, the solver might call property routines with invalid inputs when it tries to find a solution for a system of non-linear equations or when it test a large step-size.

In the external interface we decided that it should be the property calculator responsibility to handle this as different property types such as e.g. transport and equation of state based properties may have different validity regions and might be a function of composition.



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