Problem in species transport model

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anshs posted this 2 weeks ago

I'm using an Eulerian Multiphase model to simulate a system where I'm studying transport of species between 2 phases.

My 2 phases are defined like this: 
 

I'm running a simulation with the following initial conditions: 



But when I'm simulating it for species transport (transient analysis) without anything else (i.e no reaction involved), I'm getting new species as products . i.e I don't know how and why SO2 is being produced in the domain!




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abenhadj posted this 2 weeks ago

A post processing issue if no reaction is modeled and setup is correct. Better to multiply with of fraction for better understanding but why the volume fraction is not 1 at top and bottom of the tank?

Best regards,

Amine

anshs posted this 2 weeks ago

It's 1 only, The Check the volume fraction color bar. the top oil layer ( mixture_template_oil) which is the top phase represented by red is 1e+0. 
This phase contains a. kerosene Liq ( mass fraction = 0.9), b. SO (mass fraction = 0.1)  and c. SO2 (mass fraction = 0.0). 

What do you mean by 'Better to multiply with of fraction'?

I have 1 more query, What's the difference between heterogeneous reactions in the phase interaction setup and Volumetric reaction in species transport setup? 
Which one shall I use, in order to react the species SO (of top layer) and species O2 (of bottom layer), in order to produce SO2 at the interface! 

SO (oil_phase) + O2 (water_phase) = SO2 ( at the interface, i.e in both the phases)

Thank you. 

abenhadj posted this 2 weeks ago

If there is no reaction then everything is due to phase buoyancy and species diffusion in a phase. Just post-process species mass fraction x volume fraction (create a custom field function for that).

Heterogeneous reaction is   where products and reactants do not need to be in the same phase

Best regards,

Amine

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anshs posted this 2 weeks ago

With the above setup, now I have included the following heterogeneous chemical reaction, but still, I'm not getting any result in the heterogeneous reaction rate!

 

result: heterogeneous reaction rate

abenhadj posted this 2 weeks ago

Note the limitations highlighted in the documentation: the phases need to be well mixed. What you need is an UDF for mass transfer as the mass transfer does happen at the interface or you diffuse the interface

Best regards,

Amine

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anshs posted this 2 weeks ago

Aren't the phases well mixed? because of the species mass fraction showing the same value throughout! But I don't think it will remain so that way after some reaction starts to occur! 

Could you explain something more about the UDF's. Thanks

abenhadj posted this 1 weeks ago

both phases need to be well mixed as mentioned in the documentation.

UDF: User Defined Functions. There you need to use a custom mass transfer: there is an example in the customization manual regarding water evaporation which you look into.

Best regards,

Amine

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anshs posted this 1 weeks ago

So you're saying I need mass transfer UDF to supply these species to the interface in order for them to react with each other.

But why isn't the species transport equation taking care of all these things? since I'm enabling Diffusion in this model ( Multi-component + Thermal ) in the species transport model tab.

Thanks.

abenhadj posted this 1 weeks ago

I am talking about the mass transfer between the phases. Diffusion process is taken into account by Fluent.

Best regards,

Amine

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anshs posted this 1 weeks ago

No, but if the species are only diffusing and reacting then why do I need to perform a mass transfer between the phases?

abenhadj posted this 1 weeks ago

Because you want to model heterogeneous reaction.

Best regards,

Amine

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anshs posted this 1 weeks ago

But the physics of the problem seems to me as if I only want the species to travel. I want the phase to remain as it is!

But are you meaning that the species has no independent entity and is interlinked to the phase-in itself?

 

abenhadj posted this 1 weeks ago

But the phase will change the chemical component is the same but the state is different.

Best regards,

Amine

anshs posted this 1 weeks ago

I'm sorry but I couldn't follow your last explanation! May you please try explaining it again! 
Thanks

abenhadj posted this 1 weeks ago

Component a would move from liquid phase to gaseous phase. This require a model for mass transfer in Fluent.

Best regards,

Amine

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anshs posted this 1 weeks ago

Does that mean, the species can't get transferred/ transported from 1 phase to another without the use of a mass transfer UDF? 
Thanks

anshs posted this 6 days ago

And also may you please define a 'species' and a 'phase' and how are they distinguishable in terms of fluent's species transport model?

Given a mixture of water+salt+sugar, with the conditions that 'salt' is homogeneously mixed in the water, while 'sugar' is inhomogeneously mixed in water. May you please define the phase and species respectively for this system? 

May you please answer both these questions! Thanks.

abenhadj posted this 6 days ago

Species are mixed at molecular level. Phases depict a discernible interface and might different states (not obligatory). There are immiscible. Non condensable gas is dissolved in water and so we treat this as mixture. At certain condition the gas will leave the mixture escape it to form bubbles (weak cavitation for example).

You might ask your professor for further question like this one.

Best regards,

Amine

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anshs posted this 5 days ago

 

I want to know the relation between species transport equation and VOF in multiphase flows, I've read the theory book where there is a similar term on the RHS of both these equations. Which happens to be the mass transfer term!

But I want to know that how come the species in the figure 2(b) & 2(c), come out of the defined Volume of their parent containing phase?

 




Figure 1: initial conditions on, 1(a) = VOF oil phase, 1(b) & 1(c) = Corresponding species 'ch3' and 'so' respectively.

After diffusion takes place:

Figure 2: after a while , 2(a) = VOF oil phase, 2(b) & 2(c) = Corresponding species 'ch3' and 'so' respectively.

 

abenhadj posted this 5 days ago

The phase diffuses so do the contained species according to the figure without judging the setup. That was my last comment here.

Best regards,

Amine

anshs posted this 5 days ago

But the question here is, can a species diffuse out of its parent phase, while it was not defined in any other phase? ie. does a species have independent existence than a phase? 

Thanks

abenhadj posted this 5 days ago

No: that is why you need to post-process species-massfraction*volume fraction to get it best.

Best regards,

Amine

anshs posted this 4 days ago

Hey, I followed your reply and came up with these results: 

Figure: after a while , 2(a) = 'so' species mass fraction , 2(b) = =  VOF oil phase (parent phase of 'so') &  2(c) = species-massfraction*volume fraction.

Now can you explain it to me,
(1) Why the species 'so' diffused out of the volume of it's parent phase (oil) ?
(2) The significance of the result in (c) i.e VOF*mass_fraction.

Thank you very much!  

abenhadj posted this yesterday

Numerics and Eulerian Model principles. Just quantify the species where try phase is defined.

Best regards,

Amine

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