Discussion Forum

Hi everyone, new user here.

I am trying to build a simulation of a gas nozzle (1 bar pressure, Helium) introducing a gas into a small cell (10mmx20mmx30mm), which has three small (around 1mm or 500µm diameter) openings - one for the input nozzle, two which allow the gas to leak out.
Now, in my actual experiment, the box will be in a vacuum, but since I understood that the Comsol CFD simulation uses the Navier-Stokes equations for the modeling, i.e. no long free path lengths, I will just assume a low density of Helium gas around and inside the box.
I want the simulation to show
a) the time until the box is in an equilibrium, i.e. the Helium "input" from the nozzle matches the "output" through the other two holes, and
b) the gas density distribution in this case.

Now, I watched the tutorial at www.comsol.com/products/tutorials/CFD-COMSOL-demonstration/ and tried to stick by this tutorial as closely as possible, but right now I'm stuck.

First of all, I modeled the box with six work planes, three of them have a spherical hole (created by the boolean "difference" operator) (one input, two output).
Then I built the gas inside and outside the box with another work plane and a extrusion, so the box is completely "immersed" in the gas work plane.
Next, I wanted the simulation to "know" that the gas should view the box as boundary.
So, I applied materials (Glas and Helium) to the box and the gas, and then I wanted to connect both in the "Fluid-Solid-Interface Boundary" of the Fluid-Structure-Interaction physics from the Structural Mechanics Module.
Here, all existing planes are "not applicable".
What am I doing wrong, so far?
Is there any hope for this project? Or are there fundamental flaws?
The next step would be to introduce the gas nozzle into this system, how would I go about that (it should supply Helium gas with constantly 1 bar).

Thanks very much in advance, best regards


Thomas