Issue833 extend of real pass through medium

Created by: FWuellhorst

I fixed issue #833 (closed) by applying the proposed solution.

@PMehrfeld: I checked the conversion-script by creating a small example. However im unsure what happens if someone used the model in a different way, e.g. m_flow_nominal=0.3. Is there a better way to ensure correct conversion?

Closes #833 (closed)