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Why no "Concentration source" like "Heat Source"?

I have been working on 4.2 and getting a grip on its interface since I have worked on 3.5 and other softwares before. I basically have a number of micropheres loaded with a drug. And these microspheres which are embedded inside a hydrogel and are slowly releasing the loaded drug. I want to assign these microspheres with a concentration that would vary as f(t).

I thought I could just assign the concentration of these micropsphere domains with the equation f(t), but apparently there is only option for a boundary concentration which I am not quite understanding (since I am getting wrong results with boundary concentration lol). Heat equation is essentially same as simple diffusion equation. Shouldn't the methods be same?

Would really appreciate if someone could shed some light on this.

7 Replies Last Post Oct 8, 2013, 9:32 PM EDT
Posted: 4 years ago Oct 7, 2013, 1:19 AM EDT
Hi,

Source what you looking for is "Species Source". I don't is this in version 4.2 but version 4.3b has it.

www.comsol.com/products/specifications/chemical-species-transport/

Best regards

Tero Hietanen
Hi, Source what you looking for is "Species Source". I don't is this in version 4.2 but version 4.3b has it. http://www.comsol.com/products/specifications/chemical-species-transport/ Best regards Tero Hietanen

Posted: 4 years ago Oct 7, 2013, 3:05 AM EDT
Thanks Tero. :)
But since I do not have access to 4.3b right now, is their a workaround this? I thought if I could assign the boundaries of sphere with variable flux, that might work. But apparently flux cannot be applied to interior boundaries.
Thanks Tero. :) But since I do not have access to 4.3b right now, is their a workaround this? I thought if I could assign the boundaries of sphere with variable flux, that might work. But apparently flux cannot be applied to interior boundaries.

Posted: 4 years ago Oct 7, 2013, 3:22 AM EDT
Hi,

Sorry, I don't know how to do this other way.... I have also try to found solution this (I don't have Chemical engineering module and CFD module doesn't include this) but I haven't found any good way to go around problem.

Best regards

Tero
Hi, Sorry, I don't know how to do this other way.... I have also try to found solution this (I don't have Chemical engineering module and CFD module doesn't include this) but I haven't found any good way to go around problem. Best regards Tero

Posted: 4 years ago Oct 7, 2013, 6:11 AM EDT
Hi,
It seems that the source term (the "species source" you want) is just the "Reactions" node, with which you can represent creation or destruction of the related species. It's present in raw COMSOL Multiphysics, for that you don't need additional Modules (or if you use that Chemical Reaction Eng. Module you'll have that feature for sure).
Regards,
Jesus.
Hi, It seems that the source term (the "species source" you want) is just the "Reactions" node, with which you can represent creation or destruction of the related species. It's present in raw COMSOL Multiphysics, for that you don't need additional Modules (or if you use that Chemical Reaction Eng. Module you'll have that feature for sure). Regards, Jesus.

Posted: 4 years ago Oct 7, 2013, 1:16 PM EDT
Hi Jesus,

I actually did think of that two. But isn't the reactions term made for only consumption or production? In a sense that if chemical A reacts with Chemical B to produce the species c. In my model the only thing that is happening is controlled release of drug from the microsphere into the hydrogel. So the total amount of drug in the system is same.

Although I am going to try this once more. The term "reaction" is just confusion to me lol.

Hi Jesus, I actually did think of that two. But isn't the reactions term made for only consumption or production? In a sense that if chemical A reacts with Chemical B to produce the species c. In my model the only thing that is happening is controlled release of drug from the microsphere into the hydrogel. So the total amount of drug in the system is same. Although I am going to try this once more. The term "reaction" is just confusion to me lol.

Posted: 4 years ago Oct 7, 2013, 1:37 PM EDT
Hi, Lokesh,

I had understood that you only wanted to simulate your species (drug) concentration and that the microspheres were not included in the geometry. Do you intend to include them? If so, their interior could be out of physics (diffusion), and their surfaces would then be external boundaries of the main geometry. But the prefix *micro* suggests that they are too small to take them into account in the geometry. In that case, you could simulate them simply by the drug delivering rate: f(t), if their effect is homogenous, or f(x, y, ..., t) if that drug-delivering is also a function of the position. You know where those micro-spheres are located, and how to spatially model their drug-delivering.

Jesus.
Hi, Lokesh, I had understood that you only wanted to simulate your species (drug) concentration and that the microspheres were not included in the geometry. Do you intend to include them? If so, their interior could be out of physics (diffusion), and their surfaces would then be external boundaries of the main geometry. But the prefix *micro* suggests that they are too small to take them into account in the geometry. In that case, you could simulate them simply by the drug delivering rate: f(t), if their effect is homogenous, or f(x, y, ..., t) if that drug-delivering is also a function of the position. You know where those micro-spheres are located, and how to spatially model their drug-delivering. Jesus.

Posted: 4 years ago Oct 8, 2013, 9:32 PM EDT
Hi jesus,

Thanks a lot!
You are actually right. The reaction term can be simply used as a source. I went back to comsol and stared at the equation for 10 minutes and realized I do not need a new "concentration source" term. I can simply specify it in the "reactions".

And about the microspheres, I am actually including them in the model. I will again run the simulation using the reactions term for these spheres and see results.

Hi jesus, Thanks a lot! You are actually right. The reaction term can be simply used as a source. I went back to comsol and stared at the equation for 10 minutes and realized I do not need a new "concentration source" term. I can simply specify it in the "reactions". And about the microspheres, I am actually including them in the model. I will again run the simulation using the reactions term for these spheres and see results.

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