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Mass extraction and saturation of bulk solution

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Hi all,

I am fairly new to COMSOL. I am after solving a non steady-state packed bed extractor with fluid flow convection in the axial direction of the extractor and diffusion of soluble material from the solid particles.

The first thing I am trying is to solve the diffusion equation in 2D with different boundary conditions, as if the particles were in a stirred vessel.

My question is:

When a forced convection boundary condition is imposed, how can be the saturation of the bulk fluid be accounted for?

Manually the process would be

1) Bulk concentration of the fluid is 0 at time 0
2) After the first time step has elapsed, the solution of the diffusion equation gives a total flow (mass released) out of the particle. That mass divided by the volume of the vessel gives the bulk concentration for the next time step.

In COMSOL, how can I update the bulk concentration by imposing that it would be the volume integral over the particle divided by the volume of the vessel for each time step? Is there a way to create a for loop of should I combine this problem with Matlab?

Thanks in advance

B

2 Replies Last Post May 16, 2013, 7:58 a.m. EDT

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Posted: 1 decade ago May 15, 2013, 5:05 a.m. EDT
I attach a picture be clearer about the problem.



I attach a picture be clearer about the problem.


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Posted: 1 decade ago May 16, 2013, 7:58 a.m. EDT
In case this is useful for anyone:

-The approach I followed was to solve the increment of concentration in the tank analytically
(V*dCbulk/dt = kA(Cbulk-C(t)), and define and expression with the analytical solution over the considered boundary, and then use the boundary condition "Flux" It seems to work but still I would like to know how to implement straight away a boundary condition which is a differential equation...

In case this is useful for anyone: -The approach I followed was to solve the increment of concentration in the tank analytically (V*dCbulk/dt = kA(Cbulk-C(t)), and define and expression with the analytical solution over the considered boundary, and then use the boundary condition "Flux" It seems to work but still I would like to know how to implement straight away a boundary condition which is a differential equation...

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