Pneumatic gas transportation system

Hi,

Does anybody know, how to properly model the gas flow in simscape pneumatics? Gas flow into pneumatic resistive pipe at some predefined pressure, say 30 bars. But if I use an ideal pressure generator, it creates the pressure of 30 bars in all the system, even at the end of the pipe which is not realistic, since pneumatic resistive pipe causes a pressure drop. but by using an ideal flow rate generator I cannot predefine initial pressure at the inlet of the pipe. Any suggestions how to implement this very simple case?

Answer 1

[Guy Rouleau]

What you mention is surprising. If you connect in series a reference, pressure source, an orifice (or pipe) and a reference, the pressure will be different on each side of the orifice (or pipe).

If you look at the demo model "ssc_pneumatic_actuator.mdl", there is a pressure difference at the ports of the pipes and orifices.

With the information available, it is hard to say, but I would bet the problem is in the way components are connected. Do you have a closed circuit where pressure stabilize to the same value everywhere after some time?

[Tomas Iesmantas]

Yes, in the case when there is a chain reference->pressures source->pipe->reference there will be a pressure drop, because this refere to the model where pipeline is open entirely, i.e. all the gas goes to the air directly. But my model is reference->pressure source (30 bars) -> pipeline (diam.=1 meter, length 10 km)->champer (equal to pipeline volume) -> orifice (like a tap). And the pressure drop at the beginning of the pipeline and before the orifice eventually drops to zero. Maybe this is because of the volume after the pipeline. But I think I need it in order to model gas compressibility within pipeline?

[Guy Rouleau]

You are correct, the Simscape documentation specifies that "every node should have a volume of fluid associated with it."

https://www.mathworks.com/help/toolbox/physmod/simscape/ug/br7vtpp.html#br7vtvl-1

I recommend using the Simscape Explorer to observe the pressure and flow at each node... this should help explaining where the flow is going:

http://www.mathworks.com/matlabcentral/fileexchange/28184-simscape-simulation-results-explorer

[Tomas Iesmantas]

Hi,

I found the reason why the pressure drop eventualy reaches zero: constant volume chamber, which I assumed would model the compressability of gases within pipeline, eventually fills up and all gases goes just through the orifice and not into chamber. Thats why pressure drop goes to zero - after some time there is no gas flow to the chamber. But this raises another issue: how to model (very) simple gas flow through pipeline and through orifice, because the volume after the resistive tube models something else?