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diffusion through a thin boundary layer
Posted 30.04.2010, 07:48 GMT-4 2 Replies
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I'm trying to model diffusion of a particle through a thin boundary layer. I'm using 2D axial symmetry mode and fluid dynamics and convection diffusion physics. I have a tube that has a flow inside and carries the particles from inlet to outlet. Particles may diffuse through the thin boundary layer into surrounding media. There are couple of problems that I have.
1. I want the flow to be restricted to the subdomain 1 (inside the tube). However, since I'm using a permeable thin boundary layer on one of my walls, the flow is allowed to permeate into the second subdomain which I only want the particles to diffuse. I increased the viscousity of the surrounding media to prevent convection and only allow diffusion.
2. the particle concentration inside the tube is much more higher (300 times) than the surrounding media. The result is not correct. There should be only 10-20% difference in concentrations inside the tube and in surrounding media. This can easily be prove by solving diffusion equation with neumann boundary condition on permeable wall for my initial conditions.
I also have another question:
3. In a multiphysic problem, is there any way to solve a physic in two geometries and another physic for only one of those geometries? I know the other way is possible (i.e., I can solve two physics in one geometry and one physic in a second geometry)
I would appreciate if you can help me.
Also if you have modeled a diffusion problem through a thin boundary layer and can provide me with the model, I'm sure it can help me alot.
Thanks
1. I want the flow to be restricted to the subdomain 1 (inside the tube). However, since I'm using a permeable thin boundary layer on one of my walls, the flow is allowed to permeate into the second subdomain which I only want the particles to diffuse. I increased the viscousity of the surrounding media to prevent convection and only allow diffusion.
2. the particle concentration inside the tube is much more higher (300 times) than the surrounding media. The result is not correct. There should be only 10-20% difference in concentrations inside the tube and in surrounding media. This can easily be prove by solving diffusion equation with neumann boundary condition on permeable wall for my initial conditions.
I also have another question:
3. In a multiphysic problem, is there any way to solve a physic in two geometries and another physic for only one of those geometries? I know the other way is possible (i.e., I can solve two physics in one geometry and one physic in a second geometry)
I would appreciate if you can help me.
Also if you have modeled a diffusion problem through a thin boundary layer and can provide me with the model, I'm sure it can help me alot.
Thanks
2 Replies Last Post 30.04.2010, 11:26 GMT-4
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Posted:
1 decade ago
Hi Saman,
First, I can't say I got a clear picture of what you are doing. So, if you have, please attach a schematic.
So, if it is something like a membrane, then you can divide your convection-diffusion in multiple physics: have convection in the pipe, diffusion in the boundary-layer and whatever you want in the surrounding. have the no-slip boundary for the flow on the wall, so no flow can pass inside the thin layer.
Hope I got you right.
First, I can't say I got a clear picture of what you are doing. So, if you have, please attach a schematic.
So, if it is something like a membrane, then you can divide your convection-diffusion in multiple physics: have convection in the pipe, diffusion in the boundary-layer and whatever you want in the surrounding. have the no-slip boundary for the flow on the wall, so no flow can pass inside the thin layer.
Hope I got you right.
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Hi Saman,
First, I can't say I got a clear picture of what you are doing. So, if you have, please attach a schematic.
So, if it is something like a membrane, then you can divide your convection-diffusion in multiple physics: have convection in the pipe, diffusion in the boundary-layer and whatever you want in the surrounding. have the no-slip boundary for the flow on the wall, so no flow can pass inside the thin layer.
Hope I got you right.
First, I can't say I got a clear picture of what you are doing. So, if you have, please attach a schematic.
So, if it is something like a membrane, then you can divide your convection-diffusion in multiple physics: have convection in the pipe, diffusion in the boundary-layer and whatever you want in the surrounding. have the no-slip boundary for the flow on the wall, so no flow can pass inside the thin layer.
Hope I got you right.