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Transport in diluted species

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Hi,
In my simulation there is a hollow sphere and time dependent mass transfer takes place from this sphere to the surrounding fluid. At the outer surface I am specifying the flux condition. At the inner surface my concentration should decrease with time. What kind of boundary condition can I specify at the inner boundary?

8 Replies Last Post 2015年12月8日 GMT-5 01:48

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Posted: 9 years ago 2015年11月23日 GMT-5 09:59
If a single solute transfers from the inner sphere through a wall to the exterior of the sphere, you do not need to specify any BC at the inner surface, just define the diffusion coefficient in the inner sphere and in the sphere wall. You need thus only one Transport of Diluted Species node.

BR
Lasse
If a single solute transfers from the inner sphere through a wall to the exterior of the sphere, you do not need to specify any BC at the inner surface, just define the diffusion coefficient in the inner sphere and in the sphere wall. You need thus only one Transport of Diluted Species node. BR Lasse

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Posted: 9 years ago 2015年11月23日 GMT-5 23:42
Thank you for the suggestion sir,
But, See the image attached.
I have tried what you have suggested.
Here I A have 2 concentric spheres (say s1 and s2 starting from the inner most one) over which a fluid is flowing . I have applied your suggestion of 2 diffusion coefficients in the 2 domains and on the outermost surface I have used a flux condition as fluid is flowing over.
my doubt is what condition should I specify at the inner most boundary of s1? 'No flux' condition is not working in my case. There my concentration is a function of time. I have searched a lot but I didn't get any appropriate analytical expression for time dependent concentration.
Can you provide any help in this case?
Thank you for the suggestion sir, But, See the image attached. I have tried what you have suggested. Here I A have 2 concentric spheres (say s1 and s2 starting from the inner most one) over which a fluid is flowing . I have applied your suggestion of 2 diffusion coefficients in the 2 domains and on the outermost surface I have used a flux condition as fluid is flowing over. my doubt is what condition should I specify at the inner most boundary of s1? 'No flux' condition is not working in my case. There my concentration is a function of time. I have searched a lot but I didn't get any appropriate analytical expression for time dependent concentration. Can you provide any help in this case?


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Posted: 9 years ago 2015年11月24日 GMT-5 02:30
I thought that the inner sphere is the source of the diffusing species, but in your image that is an empty cavity, i.e. it is not a part of the simulation domain?

If you need a time dependent concentration at the inner boundary, define an appropriate function under

Component --> Definitions --> Functions

Let's assume that you have defined a piecewise function that is named "pw1". Then, at the boundary call it as pw1(t).

BR
Lasse
I thought that the inner sphere is the source of the diffusing species, but in your image that is an empty cavity, i.e. it is not a part of the simulation domain? If you need a time dependent concentration at the inner boundary, define an appropriate function under Component --> Definitions --> Functions Let's assume that you have defined a piecewise function that is named "pw1". Then, at the boundary call it as pw1(t). BR Lasse

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Posted: 9 years ago 2015年11月29日 GMT-5 05:13
Thanks for the suggestion sir.
Sir,
In my model the thickness of the 2 layers decreases with time because of diffusion. So I have used the deformed geometry physics for this purpose.
In my inner layer the concentration is constant and becomes zero only when the thickness of this layer becomes zero.
When I am running the simulation with deformed geometry. It was displaying an error, 'Inverted mesh element'
Do you have any suggestion about how can I over come this?
Thanks for the suggestion sir. Sir, In my model the thickness of the 2 layers decreases with time because of diffusion. So I have used the deformed geometry physics for this purpose. In my inner layer the concentration is constant and becomes zero only when the thickness of this layer becomes zero. When I am running the simulation with deformed geometry. It was displaying an error, 'Inverted mesh element' Do you have any suggestion about how can I over come this?

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Posted: 9 years ago 2015年11月30日 GMT-5 03:00
When the thickness approaches zero, there won't be anything to be meshed. I have no clear solution to this, but if you define the thickness by a parameter, also the mesh can be parametrised. Like:

d = thickness of the layer
N = d*10 = number of layers in a mapped mesh

What kind of meshing are you using?
When the thickness approaches zero, there won't be anything to be meshed. I have no clear solution to this, but if you define the thickness by a parameter, also the mesh can be parametrised. Like: d = thickness of the layer N = d*10 = number of layers in a mapped mesh What kind of meshing are you using?

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Posted: 9 years ago 2015年11月30日 GMT-5 10:40
Thanks for the suggestion sir.
I am using free triangular mesh.
Thanks for the suggestion sir. I am using free triangular mesh.

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Posted: 9 years ago 2015年12月7日 GMT-5 06:56
Sir,
Suppose my concentric spheres are oppositely charged, is there a way I can incorporate this in my comsol model.
Sir, Suppose my concentric spheres are oppositely charged, is there a way I can incorporate this in my comsol model.

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Posted: 9 years ago 2015年12月8日 GMT-5 01:48
Hi

This is a question I have been thinkng a lot because I would like to model ion-exchange membranes that have fixed charged groups. So far I have not figured it out how to do it, and I have not found anything from this website or in the web.

BR
Lasse
Hi This is a question I have been thinkng a lot because I would like to model ion-exchange membranes that have fixed charged groups. So far I have not figured it out how to do it, and I have not found anything from this website or in the web. BR Lasse

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