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TAYLOR DISPERSON: Instantenous Pulse Release of Dillute Solute and Effective Diffusivity

Posted Mar 3, 2011, 3:10 a.m. EST Chemical Reaction Engineering Version 4.1 3 Replies

iomega15
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Can anybody tell me how to do this in COMSOL? I am new to the software. I would like to release a pulse of a dillute solute at the entrance to a 2D channel. I would like this to happen at time zero only and not at any time after that.

Also, I would like to calculate the effective diffusivity from this simulation. Please help!

PS: I know how to do everything except for these two things (I know how to get the flow field, I know how to couple a time dependent solute transfer with a steady flow field, etc)
3 Replies Last Post Mar 3, 2011, 2:42 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Mar 3, 2011, 1:07 p.m. EST
Hi

I'm not that often in the chemisty module, but if you want t input a pulse of E field or a concetration, I would use the gaussian or the step/pulse functions. You should use a smooth pulse to allow the solver to take some continuous derivatives of the changes to manage to follow. Then in a transient solver I believe you can see the decay via a probe or a line cut plot of the concetration over time. You can also define a variable to fit a decay function and get it to be optimised via a mean square by a global equation. There are a few discussions around this, for a single parameter you can do it without the optimisation module, for many parameters the optimisatin module is set up to make things quicker for you

--
Good luck
Ivar
Hi I'm not that often in the chemisty module, but if you want t input a pulse of E field or a concetration, I would use the gaussian or the step/pulse functions. You should use a smooth pulse to allow the solver to take some continuous derivatives of the changes to manage to follow. Then in a transient solver I believe you can see the decay via a probe or a line cut plot of the concetration over time. You can also define a variable to fit a decay function and get it to be optimised via a mean square by a global equation. There are a few discussions around this, for a single parameter you can do it without the optimisation module, for many parameters the optimisatin module is set up to make things quicker for you -- Good luck Ivar
iomega15
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Posted: 1 decade ago Mar 3, 2011, 1:49 p.m. EST
I don't know how to use functions, thats what I am saying. Can you give me an example of how to write a gaussian pulse as a function of time, where it is released at time zero and not released at any time after that? Thanks.
I don't know how to use functions, thats what I am saying. Can you give me an example of how to write a gaussian pulse as a function of time, where it is released at time zero and not released at any time after that? Thanks.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Mar 3, 2011, 2:42 p.m. EST
Hi

in v4 you g undr the Definition node (right click) therein you have also functions, try them out, they are documented in the help files and the doc, you can plot them too to see how they behave.

Be curious and open up all hidden/closed sub-levels there are more things in there sometimes slightly hidden to make it simpler to navigate (and in v4 try a right click about everywhere ;)

--
Good luck
Ivar
Hi in v4 you g undr the Definition node (right click) therein you have also functions, try them out, they are documented in the help files and the doc, you can plot them too to see how they behave. Be curious and open up all hidden/closed sub-levels there are more things in there sometimes slightly hidden to make it simpler to navigate (and in v4 try a right click about everywhere ;) -- Good luck Ivar

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