Gas containment with output

Hello, I'm modelling gas flow system and what is quite strange that SimHydraulic doesn't have any container with output: constant volume chamber has just input port. Maybe it is possible to construct with simulink blocks some chamber (like constant volume chanber), but with output orifice? Or maybe it is possible to use other blocks (even I couldnt find any) to use instead?

Answer 1

[Arnaud Miege]

SimHydraulics is not designed for modelling gas flow systems, only (hydraulic) fluids. You can use the Simscape pneumatic foundation library instead. Note that it uses the ideal gas law approximation. More details are available in the documentation.

HTH,

Arnaud

[Tomas Iesmantas]

But if I use hydraulic fluid with parameters (density, viscosity and so on.) of gas under consideration? Isn't that valid?

[Arnaud Miege]

No it isn't. The fluid properties are different. For a start, SimHydraulics and the Simscape hydraulic foundation library assume a constant temperature throughout the hydraulic network and also for the duration of the simulation. The pneumatic domain, on the other hand, includes thermal effects. You can see this by looking at the domain definition files, where the hydraulic one only has one across and one through variables (pressure and volumetric flow rate, respectively), whereas the pneumatic one has 2 of each (pressure & temperature + mass flow rate & heat flow). The domain-wide parameters are also different between the two domains.

[Tomas Iesmantas]

Well, acctually I don't care about temperature process in gas. I just need pressure loss when hydraulic fluid (assumed gas)goes throught several local resistance elements and flow rate.

But still, back to my question. Even in simscape pneumatic foundation library there are no chamber-like block that would have some output orifice, just input (Constant Volume Pneumatic Chamber).

[Arnaud Miege]

So if understand correctly, you would like to model a pneumatic chamber with an inlet port and an outlet port, is that right? The source code for the Constant Volume Pneumatic Chamber is available (double-click on the block and then click on "View source for Constant Volume Pneumatic Chamber"), so using the Simscape language, it might be possible to adapt the code to create a new version, with two pneumatic ports. I suspect the equations will need to be modified slightly.

[Tomas Iesmantas]

But unfortunately, there is no way to view source code for hydraulic chamber. Maybe you have any sugestions for hydraulic systems? ( something like two-port Constant Volume Hydraulic Chamber, I mean).

[Arnaud Miege]

Don't use the hydraulic blocks for pneumatic simulations, the equations are different for hydraulic and pneumatic systems - and the assumptions used to derive those equations are also different. Forget about the hydraulics for your problem.