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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Diffusion in two layers!

Posted 2015年2月17日 GMT-5 07:43 Version 4.4 4 Replies

Mikael Hedenqvist
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Hi, I am pretty new on Multiphysics. I want to make a solid sphere with two layers. I want to calculate the mass uptake in the inner layer (from origo to the border between the layers). As a first approximation there will be two diffusion coefficients but the same solubility in both. The boundary will be a continous flux (in the next case two different solubilities will be used). How do I set up the system. As I understand there are various ways of doing this, two components, two physics and two domains, please advise how to make sucg systems.
4 Replies Last Post 2015年2月24日 GMT-5 04:08
Lasse Murtomäki
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Posted: 10 years ago 2015年2月17日 GMT-5 09:12
Hi

1. Make an axisymmetric 2D-model.
2. Draw a semicircle with a desired layer thickness.
3. Mesh across the boundary very densely (attached).
4. No boundary condition needed between the domains.
5. Initial concentration in the inner sphere = 0.
6. Compute with logarithmic time step, because initially there is an enormous concentration gradient across the boundary.
7. Surface integration in the inner sphere, activate "Compute volume integral".
8. Check that the total amount = volume integral over entire geometry = constant = 4/3·pi.

Thus, only one physics (Transport of Dilutes Species), one component. I make always dimensionless models, if possible, like this:

R = r/r0 (r0 = outer sphere radius)
D = 1, because
T = Dt/r0² (dimensionless time)
C = c/c_init (c_init = initial conc. in the outer sphere)

At T = 0.1 80% of the material is in the inner sphere.

br
Lasse
Hi 1. Make an axisymmetric 2D-model. 2. Draw a semicircle with a desired layer thickness. 3. Mesh across the boundary very densely (attached). 4. No boundary condition needed between the domains. 5. Initial concentration in the inner sphere = 0. 6. Compute with logarithmic time step, because initially there is an enormous concentration gradient across the boundary. 7. Surface integration in the inner sphere, activate "Compute volume integral". 8. Check that the total amount = volume integral over entire geometry = constant = 4/3·pi. Thus, only one physics (Transport of Dilutes Species), one component. I make always dimensionless models, if possible, like this: R = r/r0 (r0 = outer sphere radius) D = 1, because T = Dt/r0² (dimensionless time) C = c/c_init (c_init = initial conc. in the outer sphere) At T = 0.1 80% of the material is in the inner sphere. br Lasse

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Lasse Murtomäki
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Posted: 10 years ago 2015年2月18日 GMT-5 07:04
Hi

And the model file.

Lasse
Hi And the model file. Lasse
Lasse Murtomäki
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Posted: 10 years ago 2015年2月24日 GMT-5 01:46
I have only version 5.0.

br

Lasse
I have only version 5.0. br Lasse
Mikael Hedenqvist
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Posted: 10 years ago 2015年2月24日 GMT-5 04:08
OK, thanks anyway,

Regards

Mikael
OK, thanks anyway, Regards Mikael

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