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Combination of multicomponent/multiphase for a mixing vessel

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Old   June 28, 2015, 11:56
Default Combination of multicomponent/multiphase for a mixing vessel
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I am simulating the mixing behaviour in a mixing vessel. Therefore I am using VOF to implement the free surface at the top of the mixing liquid (see Image 1 and 2).
To track the mixing I intended to define the mixing liquid as a mixture with two times the same material. So I can define an upper and a lower mixing liquid with a cel-function for the mass fraction of each one (see Image 3).

The problem I am facing is, that I can define one of the liquids as wished but the other one needs to be set as constraint (typical for multicomponent).
This sets the constraint mixing liquid2 to the mass fraction 1-mass.fraction(liquid1) everywhere to sum up to mass fraction=1.
Which means, it sets mass fraction of liquid2 also in the area where Volume Fraction of the mixture liquid is 0 (above the surface, in the air). (see Image 4).

Hope, it is more or less understandable what I am trying to do here.

So far, I don't see a way to solve this. How is it possible to combine Multiphase and Multicomponent?

I'd really appreciate any advice here!




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Old   June 29, 2015, 10:40
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It is definitely possible to model multiphase flow where each phase is a mixture of materials.

When describing such complex setup, it is extremely helpful to keep the vocabulary straight about phases and multicomponent materials. For example,

Phase A is made of Material M1, M2, and M3

Phase B is made of Material M3, M4, and M3

I assumed that there should be at least one common material between the phases, such as it can migrate from one phase to another.

Also, not sure why you want to make the phase a multicomponent material if it is not part of the physics. If you need a tracer, you can create an "Additional Variable" which is a passive scalar and it does not have the requirement to be constrained to another passive scalar.

Hope the above helps,
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Old   June 29, 2015, 11:01
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Thanks for the reply!

The configuration is as followed:
Phase A: Air (above free surface)
Phase B: Liquid 1 and Liquid 2 (below the surface).

Phase A and B don't interact. But the free surface (based on the vortex -> Image 2) is important for the mixing behaviour.
I'd like to define the case like this because that's how I set up the experiment. Two times the same liquid with different colors.
Using the multicomponent method for the mixture would give me the possiblity to trace and visualize the mixing (for example by monitoring the mass fraction of one liquid).

But because of the constraint function for multicomponent it defines the sum of the mixture mass fraction in the whole domain, also above the surface.
How should that be approched?
I considered using a subdomain and algebraic equation instead of constraint. But so far I wasn't sucessful.

Thanks in advance,
Thomas
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Old   July 1, 2015, 07:27
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Anyone? I'd appreciate any kind of advice here!
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