Learning Forum

[Akor]

[Surya Deb]

Hello, nI would recommend to model the thin membrane as a Porous Jump condition. That way, you should be able to provide the Face Permeability value. Porous Jump is a 1D simplification of the porous zone approach. If you have an idea of the pressure drop with flow rate across the thin membrane, then you can make use of it. nPorous Jump incorporates the resistance due to momentum but not due to any diffusion process. So a diffusion resistance might be provided using diffusivity UDF in cells neighboring the porous jump. You will need to check this. nAlso please make sure that the mass diffusivities are properly set for the Oxygen diffusion in blood. And also make sure to correctly setup the phases (gas and liquid) along with the species components.nHow do you model the thin membrane currently? nI hope this helps.nRegards,nSuryann

[Akor]

Hi Surya . Thanks for the Feedback. I will incorporate these and ask more questions if I need further clarification.nThe thin membrane is a pdms layer. I tried modeling it as a fluid and turning on porous zone but that didn't help. But right now, its just pdms. I included an image of what I have for the membrane. nMy Model overall is 3D. Can I used the porous jump for 3D? or I will have to simplify my model to 2D?nAlso, any comments on the Physics of Species Transport and if you think I am doing it right?nThanks alot!n

[Surya Deb]

Hello , nYes Porous jump can be used with 3D as well. No issues with that.nThe Species Transport setup for this model should be straightforward if I am getting the problem correctly.nI would suggest you to test the results against any test/experimental data that you may have as a benchmark.nRegards,nSuryann

[Amine Ben Hadj Ali]

Will the membrane be permeable for all components?n

[Akor]

. The membrane should only be permeable to Oxygen.n

[Akor]

. When I incorporate porous jump to the model and run the calculation, Fluent shuts down for some weird reason, any thoughts? I included an image that shows the error. I was only able to take a screenshot and not copy the entire error message.nn

[Akor]

So I read online that the porous jump condition should be used for a face, not a cell zone. Apparently, I am not given the option to change my interface to a porous jump condition (under type, towards the bottom of the image). Any thoughts?nn

[Amine Ben Hadj Ali]

Can you highlight the region which is supposed to be the membrane? Why are you using interfaces and non-conformal mesh?nBy the way if the membrane is allowed to let one component flow and block the other one, you will require some UDF treatment to deal with that. n

[Amine Ben Hadj Ali]

What is that empty space? Is it another cell zone?n

[Akor]

. The empty space is the thin membrane (another cell zone). Because it is modelled as a solid, it doesn't show when I am looking at the concentration distribution. nTo answer your question on why I am using interfaces - When I use the interior-membrane, and change the type to porous-jump, Ansys shuts down when I run the calculation. n

[Amine Ben Hadj Ali]

Why it is modeled as solid zone?n

[Akor]

. He is what comes up for the membrane, although I selected a 3D filled membrane when meshing.nn

[Akor]

. Its solid because I am using a pdms material. Should it be otherwise? What do you advise?n

[Amine Ben Hadj Ali]

Can you please issue share topology in SpaceClaim in order to end up with conformal mesh? The membrane should be fluid zone right?nIn Fluent you can change the type into Fluid (check under Cell Zones and not Boundary Zones) but I recommend double checking the names and enforce multi-body-part part meshing by sharing topology in SpaceClaimn

[Amine Ben Hadj Ali]

You need please to describe your problem from scratch...nIf it is modeled as solid you cannot use species transport in that zone!n

[Akor]

. Okay, I will start the problem from scratch, and implement all these. I'll provide feedback soon. I do appreciate your help!n

[Akor]

. I was able to fix all the issues with the model and it comes out fine. The next step is working on the UDF. Do you have an links to UDFs on gas diffusion, something that I can get started with or some place to look? I looked at the UDF manual, and didn't get anything much.n

[Rob]

The manual will have examples of most things, otherwise we do offer (paid for) training. n