Thermal Expansion of Flowing Gas Changing Pressure


I am trying to run a basic simulation on the temperature change of compressed nitrogen as it leaves the pressurized environment. I have a simple tube setup with a small and a large end and am using a pressure inlet and a pressure outlet (and no-slip walls by default), but the simulation keeps failing. I am using the convective heat transfer analysis.

project link (hopefully this works):


Hi @RichieKass!

Nice project you got there, very interesting! Intuitively I would say if you know the flow rate (and the velocities lets say at the outlets) you can use a pressure inlet with zero gauge pressure. The mass flow rate at the inlet will be correct (continuity) and pressures will be relative to the inlet and the setup should be well posed. Let me have a closer look at it and get back to you with a fix.

Do you have a clue @Get_Barried & @vgon_alves?




That’s the thing, the only information I have about the system is the gague pressure of the nitrogen tank (and that the output is open air, so 0 gague pressure). I was hoping to get the local temperatures from that (and an output velocity would be nice, but isn’t critical).
I guess I’m just not sure if assigning input and outputs pressures is sufficient to define that.

Amazing response time btw.


Thanks for the feedback @RichieKass! :slight_smile:

We’ll have a look at your setup and see if we can achieve something with the given input parameter.

Keeping you up-to-date!



Hi everyone,

Copied the project over to see if I can get it running.




Hi @Get_Barried,

maybe try turning off Boussinesq and if that does not work we can try ramping the inlet as we usually do.




Hi Guys, I think the type of simulation should be changed to compressible, the solver is better-suited to highly compressible flows, there is no convection here. Try with laminar, slip walls and increase complexity from there.

Good luck!

Edit: but still ramp as suggested by Jousef