Learning Forum

[nkrpandian]

Hello everyone!nI am simulating blood flow in a vein (3D). I want to calculate the oxygen transport happening in the vein, where oxygen is absorbed by the vein walls. I felt this was a straight forward problem where I can add the diffusion coefficient, inlet oxygen concentration in the blood, whether oxygen is also transported by convection and the wall boundary condition as mass flux or a reaction. nI was able to simulate this problem with out the wall boundary condition. I gave the inlet BC for oxygen as a specific mass fraction. The diffusivity was defined in the material definition dialog box. And I solved the setup, which gave uniform distribution of oxygen in the vessel,nI am having confusion in giving the wall BC. Do I need to choose wall surface reactions? what about solid species (used for species deposition) and site species (for wall surface reaction)? I do not find an option to give the wall flux/reaction at wall boundary condition options.nMass transfer was very straight forward in another numerical software in which I had simulated the 2D problem, am I missing something in ANSYS?nAny help will be much appreciatedn

[DrAmine]

If you know the flux of species at the wall you can provide as a source term (volumetric) in the first cell layer near the wall. Other option will be to use a DEFINE_PROFILE to provide the mass fraction there but provide as input a function depicting the diffusing flux of the specie.n

[nkrpandian]

I tried solving the problem with and without specifying the wall mass fraction. When I provide mass fraction at the walls, it seems there is no effect of convection. Image one is with wall mass fraction and image 2 is without mass fraction.nI am looking to model some thing like this - https://www.youtube.com/watch?v=wSBE-TZmm7k.nI also need to include more complex geometry, this is just a starting point. I am not sure if I can use the source term on a layer of cells as my final geometry has very thin cross sections where only one cell (I use quadratic elements to negate this) with present at the wall.n

[DrAmine]

I still think you can deal with that using source terms.nBoth images are different and have different scaling.nn

[nkrpandian]

Yes, both results are different. But I do not see the effect of convection mass transport in the first one, which is a bit confusing.nnHow do I add a source term? where is that option available, is it in boundary conditions.n

[DrAmine]

Yes best to do with a UDF which will add source term in the first layer of cells near the wall. Or you separate the first layer at the wall and use directly sources terms in the GUI.nProviding the mass fraction at wall is just a boundary condition for mass fraction at the wall.nAlternative is to use a profile for mass fraction as UDF. Assume the governing equation is D??m/?y+J?m=0. D, J are known. Here you can provide m (being mass fraction) as sort of solution of that equation.nnA lot of ways..n