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Stirred Vessel with Comsol

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Hi Everyone,
I'm trying to model a standard stirred tank with a rushton impeller, and I'm finding it quite a difficult task!

The system is in a full laminar regime for stirred tanks ( Re < 10 )

I started with a simple 2d model using the moving mesh (ALE) and very small length scale (impeller diameter is about 10^-3 m, rpm imposed so that Re = 1), following guide lines given in the documentation for Deformed Meshes and Incompressible Navier-Stokes.
I was able to run a transient simulation of an impeller rotating in a cylindrical geometry, even though problems arise as I try to get closer to Re = 10. I guess I'm not running the model with optimal solver or mesh parameters, since it's still a laminar problem.

When I tried a 3d model using the same approach I was never, ever able to get initial values...
Has anyone (succesfully) tried such a simulation? I'm starting to think that maybe a full 3d fluid simulation with moving mesh is too much to handle for COMSOL, even for "small" systems.

Thanks for any answer!

2 Replies Last Post Nov 1, 2010, 8:47 AM EDT
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Hello Marco Formisano

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Posted: 10 years ago Jan 12, 2010, 7:21 PM EST
Hi Marco!

Good day to you! Currently I have been trying to simulate laminar CSTR, which is quite close to a (batch) stirred tank reactor.

Same as you, I was successful in 2D but not in 3D. Problem arises when it cannot get initial values.

Currently, I am trying to take things step-by-step. First, now I am trying to solve only the incompressible NS, which is pretty successful for steady-state analysis but not for transient. In transient state, the error that I have been getting consistently is "Failed to find consistent initial value".

I tried to use UMFPACK solver, listening to the advise found in this forum, but it failed after taking about 5 days to run, due to lack of memory.

Right now, I decided to halve my 3D CSTR along the plane of symmetry to speed up the computation. I am still working on it.

How about you? Have you found any solution?

Hi Marco! Good day to you! Currently I have been trying to simulate laminar CSTR, which is quite close to a (batch) stirred tank reactor. Same as you, I was successful in 2D but not in 3D. Problem arises when it cannot get initial values. Currently, I am trying to take things step-by-step. First, now I am trying to solve only the incompressible NS, which is pretty successful for steady-state analysis but not for transient. In transient state, the error that I have been getting consistently is "Failed to find consistent initial value". I tried to use UMFPACK solver, listening to the advise found in this forum, but it failed after taking about 5 days to run, due to lack of memory. Right now, I decided to halve my 3D CSTR along the plane of symmetry to speed up the computation. I am still working on it. How about you? Have you found any solution?

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Posted: 9 years ago Nov 1, 2010, 8:47 AM EDT
Hi Marco and Minghui,

I'm dealing with the exact same problem without any success. In particular I am interested to move a permanent magnet above a conducting plate and I have coupled the ALE moving mesh and quasi-static magnetic module. In 2d I can solve the model but in a 3d transient simulation I always end up with the error " failed to find consistent initial value". Although I have solved the model for the stationary case and used the solution as the initial value for time dependent case. Did you finally solve your problem? if so what did you do, I would appreciate if you can help me with my problem.

thanks in advance


Azar
Hi Marco and Minghui, I'm dealing with the exact same problem without any success. In particular I am interested to move a permanent magnet above a conducting plate and I have coupled the ALE moving mesh and quasi-static magnetic module. In 2d I can solve the model but in a 3d transient simulation I always end up with the error " failed to find consistent initial value". Although I have solved the model for the stationary case and used the solution as the initial value for time dependent case. Did you finally solve your problem? if so what did you do, I would appreciate if you can help me with my problem. thanks in advance Azar

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