Hello,

I am currently working on my bachelor thesis which thematises industrial compressed air systems and possibilities of making them more energy flexible. For modeling I use the modelica-based program SimulationX.
I started with a very simple model to familiarize with the software. Here, a pressure source (atmospheric pressure of ca. 1 bar) supplies a screw compressor which compresses the air to a certain pressure (here ca. 2.7 bar). Subsequently this compressed air flows through a pipe and after that directly to the exhaust of this small system. Very simple....you should think.
But the pressure at the end of the pipe was already reduced to the atmospheric pressure. The pipe itself can't be the reason for that, it is simply too short to cause such a flow loss, its surface roughness is also very small. I controlled also all the properties of the model elements and the simulation in general, they all should be fine.
When I removed the pipe, so that the compressed air flows directly from the compressor to the exhaust, the pressure of the 'compressed air' is also ca. 1 bar after it left the compressor. This also happened after I had repeated the simulation with the pipe still in the system, which didn't reduce my confusion really..... But a correct volume flow is still supplied by the compressor.
Interestingly, there is a quite similiar example model in the programm, ready for simulation. Here, instead of an exhaust, a second pressure source is put in at the end of the system. After a simulation, the pressure in the system corresponds to the required and expected value. When I replaced the second pressure source with an exhaust, the same problems appear which I experienced with my own model.
But this can't be the way it all works, because the pressure should come from the compressor and not artificially from that pressure source.

So my question is:
How does SimulationX (or similiar programs like OpenModelica, MATLAB Simulink etc.) handle fluids in general? What are your experiences with SimulationX? Does the software sometimes act arbitrarily? Or do I consider something wrong here? I assume and expect that the compressor generates the pressure and leads the related volume flow to the following components of the pneumatic system so that they can further exploit it.

Please click on the picture below to have a view on the model, it opens in an extra tab (went a little bit too big for the forum...)
The signal blocks with the functions which are connected to the compressor are for its control (Switch on/off by a 0/1-signal and the rotations per minute).

I would be very, very much thankful for an answer! I know that this is the forum for OpenModelica, but it is hard to find someone on the internet which knows about SimulationX well, so I try my luck here

Best regards!
BlackGin