Species transport through porous zone


I am modelling a storage building in Fluent in which air with a certain CO2 mass fraction enters the building via an underground channel, then the air goes up through a porous zone (pile of produce) into the headspace and out of the building.

I am using a transient 2D model. I defined a CO2 mass fraction as the inlet boundary condition for CO2. I used the default wall boundary conditions. I also defined a CO2 mass source in the solid part of the porous zone. I patched a certain (constant) CO2 mass fraction in all zones of the geometry before solving.

However, there seems to be no transport of CO2 over the boundaries of the porous zone. The CO2 mass fraction is higher in the porous zone due to the source term, but this CO2 seems to be trapped in this porous zone and doesn't get transported into the headspace. In the headspace the CO2 mass fraction stays the same as the patched value.

Can anyone help me with this? What am I doing wrong?

Thanks in advance for your time!

Kind regards,


Best Answer


  • RobRob UKForum Coordinator

    Check you actually have flow through the domain. The common error is to forget to share the topology of the parts so there's no flow path.

  • Hi Rob,

    Thanks for the tip, but the flow is going through the domain. This doesn't seem to be the problem. Any idea what else I can check?

  • RobRob UKForum Coordinator

    Can you run a pathline (streamline in CFD Post) through too? Are you adding mass as well as CO2 in the source region? How does that compare to the inlet mass flow (total, not just CO2)?

  • Yes, I am able to run a pathline through:

    and I used both a mass and a CO2 source, is that wrong?

    This is the overview of the mass flow rate balance:

    Can anything abnormal be seen from this?

  • RobRob UKForum Coordinator

    No, that's correct. If you only add a species source Fluent tends to convert mass rather than adding it.

    Looking at the concentration graph stop the CO2 on the inlet and see what happens, I'm wondering if the result is masked by the scale. You've got a max change of about 2 in 6,300. Altering the scale may help too.

  • Hi Rob,

    I'm not sure if this is what you suggested: at t=0.0003s I stopped the solution, set the species inlet BC for CO2=0 and I patched CO2=0 in the ventilation channel that is underneath the porous zone. That way air without CO2 enters the porous zone. Then I started the solution again. These are the plots:

    Area weighted average CO2 mass fraction in the porous zone:

    Area weighted average mass fraction of CO2 in the headspace:

    From the plot of the headspace I think that the CO2-production in the porous zone will eventually result in a rise of the CO2-mass fraction in the headspace, but that I just need a much longer period of time to see that result. Is that correct? Or can something else be concluded from these plots?

  • Thank you for all the help, Rob! I'll follow your advice!

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