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Mixing two fluids with static mixer

Posted Dec 23, 2011, 2:49 p.m. EST Fluid & Heat, Microfluidics, Mesh Version 5.2 5 Replies

Shaun Ensor
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I'm attempting to model two fluids mixing through a static mixer. I'm using two Laminar Flow physics for each fluid and the Transport of Concentrated Species to get an idea for when it's fully mixed by mass fraction.

However I keep getting all sorts of meshing errors when it attempts to "create free mesh" (which generally takes about 15 minutes on i5 processor, 16gb RAM) that I believe is a result of the Transport of Concentrated Species physics.

I attached the model for reference if it helps. I'm new to COMSOL and the art of meshing. Can anyone lend a hand?

Thanks!

Attachments:

5 Replies Last Post Dec 7, 2016, 2:14 p.m. EST
Shaun Ensor
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Posted: 1 decade ago Dec 28, 2011, 10:41 a.m. EST
The Laminar Flow boundary conditions in the first attached files went missing for some reason. I've attached the correct file.

Whenever I run the study it creates a new mesh that fails due to "Internal error in boundary respecting." Any ideas where it's going wrong?

Thanks.
The Laminar Flow boundary conditions in the first attached files went missing for some reason. I've attached the correct file. Whenever I run the study it creates a new mesh that fails due to "Internal error in boundary respecting." Any ideas where it's going wrong? Thanks.

Attachments:

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 28, 2011, 3:16 p.m. EST
Hi

I must say I do not really understand your model, rather I do not understand how the two SPF physics interact as they solve on the same domain,"as if they where alone". But this could also be a lack of knowledge from my part, I have never had time to follow and intensive chemistry training course, as this is not my "everyday cup of tea".

Then why 2 mesh with a scale of 2 in between ?, obviously the second mesh is not being resolved correctly from the error message.

An interesting issue though mixing two products like that, but I notice I cannot find either any examples in the model library. My advice would be to ask for some "advanced advice" directly to COMSOL "support". But there are certainly also other out here with a better knowledge of these physics/chemistry than me ;)

--
Good luck
Ivar
Hi I must say I do not really understand your model, rather I do not understand how the two SPF physics interact as they solve on the same domain,"as if they where alone". But this could also be a lack of knowledge from my part, I have never had time to follow and intensive chemistry training course, as this is not my "everyday cup of tea". Then why 2 mesh with a scale of 2 in between ?, obviously the second mesh is not being resolved correctly from the error message. An interesting issue though mixing two products like that, but I notice I cannot find either any examples in the model library. My advice would be to ask for some "advanced advice" directly to COMSOL "support". But there are certainly also other out here with a better knowledge of these physics/chemistry than me ;) -- Good luck Ivar
Shaun Ensor
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Posted: 1 decade ago Dec 28, 2011, 4:58 p.m. EST
Thank you for the reply.

The flow through the static mixer diffuses the fluids together, there's no chemical reactions. There is a laminar_static_mixer model that I've used as a guide but unfortunately that's not mixing two different fluids. I have the two SPF physics based on a model I saw on the forums of hydrogen mixing with Air in a room (www.comsol.se/community/forums/general/thread/20821/). With my limited knowledge of COMSOL this seemed to be a logical solution path.

The second mesh is created as a result of the solver and I don't know why. I have this same concept working on another model with just the tube without the mixer baffles so that leads me to believe my troubles are a result of the complicated geometry.

I'll try contacting COMSOL support directly, thanks for that advice.
Thank you for the reply. The flow through the static mixer diffuses the fluids together, there's no chemical reactions. There is a laminar_static_mixer model that I've used as a guide but unfortunately that's not mixing two different fluids. I have the two SPF physics based on a model I saw on the forums of hydrogen mixing with Air in a room (http://www.comsol.se/community/forums/general/thread/20821/). With my limited knowledge of COMSOL this seemed to be a logical solution path. The second mesh is created as a result of the solver and I don't know why. I have this same concept working on another model with just the tube without the mixer baffles so that leads me to believe my troubles are a result of the complicated geometry. I'll try contacting COMSOL support directly, thanks for that advice.
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Dec 29, 2011, 12:52 p.m. EST
The second mesh “Mesh 2” is created because your Step 2 stationary solver specifies it. You can change that to the first mesh “Mesh”. The error you are getting is because the Multigrid solver (part of the iterative solver) cannot create its internal mesh. You can fix that by refining the original mesh or choosing a solver that does not use Multigrid.

I did not look at the model in details but I share Ivar’s concern that you cannot model the mixing of two fluids like that. You need a multiphase CFD model.

Nagi Elabbasi
Veryst Engineering
The second mesh “Mesh 2” is created because your Step 2 stationary solver specifies it. You can change that to the first mesh “Mesh”. The error you are getting is because the Multigrid solver (part of the iterative solver) cannot create its internal mesh. You can fix that by refining the original mesh or choosing a solver that does not use Multigrid. I did not look at the model in details but I share Ivar’s concern that you cannot model the mixing of two fluids like that. You need a multiphase CFD model. Nagi Elabbasi Veryst Engineering
Gil Hezkia
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Posted: 8 years ago Dec 7, 2016, 2:14 p.m. EST
Hello

I've got the same problem. I want to mix 3 different liquids; Water,Brine and Glycerin,flowing through 3 different inlets each into a single domain. I haven't found any relevent tutorials (which is rather surprising,because mixing between several different liquids is a very common and rather trivial set of problems).

I'd like to ask anyone who modelled this kind of problem to share their solution or at least share the basic outlines to creat one.

Very much appreciated!

Hello I've got the same problem. I want to mix 3 different liquids; Water,Brine and Glycerin,flowing through 3 different inlets each into a single domain. I haven't found any relevent tutorials (which is rather surprising,because mixing between several different liquids is a very common and rather trivial set of problems). I'd like to ask anyone who modelled this kind of problem to share their solution or at least share the basic outlines to creat one. Very much appreciated!

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