[lakshmi.bala]

Hi All

I am trying to simulate mixing between 2 fluids (Fluid A &B) in microchannels. I am currently using the species model to study diffusion of these 2 fluids to study their interaction and how mixing is enhanced. For my preliminary model, I tried to specify the mixture constituents as waterA and waterB. However in my boundary condition window I only get 1 kind of fluid where the mass fraction can be specified. I would like to know if I am missing out on some other functions in the previous steps thereby disabling the 2nd fluid to show up in my boundary condition window.

I am new to the species model and have been trying to figure this out for the past few days to no avail.

Best Regards
Lakshmi

[CeesH]

Hi,

I think you are confused between multiphase and multi-species simulations.
In multi-species simulations, the fluid is treated as a single liquid phase; for all flow modelling purposes, there is only one liquid. The species model is concerned with the transport of species within this phase, where it is assumed that your species are completely miscible. Reading your problem statement, I do assume this is what you want.

To set up such a simulation, enable the species-model and the appropriate diffusion tabs in that model. Then, specify a mixture under materials: the mixture contains a list of species (names), where you can add, in your case, WaterA and WaterB. The bottom of the list is always the bulk species. Then, you can specify in the boundary conditions what the mass fractions of each dilute species is there (the bulk is always 1 minus the rest - so if you have 2 fluids, you will only need to specify one).

Does that answer your problem?

Best,
Cees

[sbkashif]

Hi

Given the two components are treated as a single phase and assumption that the two species are completely miscible, how does the results given by this model, say mass fraction, signify that mixing has taken place and to what extent has the mixing taken place.

[LuckyTran]

Mass fraction is nearly synonymous with species fraction (differing only by a molecular weight). The local mass fraction tells you (almost) exactly how much mixing, quantitatively. If you started with a species fraction of 1 for component A and 0 for component B and you ended up with 0.5 for both A and B then the two components are completely mixed. Of course you need not start with 1 and 0 you could start with arbitrary amounts of A & B.

[sbkashif]

Dear Mr. Tran,

Thank you for your prompt response. I have got an insight into the quantification of mixing.

Please allow me to extend my question a bit.

Consider the case of a non-reactive gaseous mixture.

As per the simulations I have carried out, the mass fraction do change and is available separately for both the components.

What do you think is the factor contributing to this change?

It is noteworthy that all the components are assumed to move at the same velocity(the assumption made by the species transport model as per the literature), then what is the factor according to you which is contributing to decrease in quantity of one gas and increase in another.

[LuckyTran]

I don't quite understand why there would be any confusion of what causes mixing in a transport equation from a numerical simulation, assuming it is error free. The physical mechanisms responsible for the transport are explicit in the governing equation itself (advection, diffusion, sources, and sinks). If we were discussing physical measurements and got odd results we could question the physics, but in a numerical simulation where the physics are "selected", what is there to question?

[pmechz]

hi ...
would u plz help me?
I want to simulate mixing of Two fluids.
but by using species transport model, how can i allocate constant value to properties of each component?


best regard

[manoj.dundi]

Good evening Cees sir,

I am using micro T channel for mixing two species. species A from one inlet and species B from other inlet. Both are having water properties.
inlet diffusion is selected under species transport. steady laminar flow model is used.

The solution is not converging for continuity for the above settings even when a residual of only 10^-03 is used for continuity.

Thanks and regards,
Manoj

[arulmechmb]

hi, i am new for species model. i can't understand the basic concept of this model.
Please, anyone, help me. how to study the basic physics and its equations with explanations.
Also setup procedure.
Thanks for advance.

[LuckyTran]

Originally Posted by arulmechmb

hi, i am new for species model. i can't understand the basic concept of this model.
Please, anyone, help me. how to study the basic physics and its equations with explanations.
Also setup procedure.
Thanks for advance.

The species transport equation is a transport equation. You can derive it for example, but simply invoking the Reynolds transport theorem.

https://en.wikipedia.org/wiki/Reynol...nsport_theorem

The basic physics is, you have a transport variable that moves around with the flow (advection in space-time). But as it moves around, it can also undergo some other physical processes (such as diffusion, or spontaneous reactions) and so on and so on.

It looks a lot like Navier-Stokes (which is a momentum transport equation) or the energy equation (which is an energy transport equation). The difference is that you have a different transport variable. In N-S it's momentum. In energy it's energy. In species transport, it is the species mass fraction (which is like a concentration).

The other difference is you need constitutive models to model any physical effects. In momentum transport you need something like a Newtonian/Stokes fluid. In energy transport, you need Fourier's law. In species transport, you need Fick's law to model the diffusion of species. Any chemical reactions show up as source terms in the species transport equation.

[arulmechmb]

Originally Posted by LuckyTran

The species transport equation is a transport equation. You can derive it for example, but simply invoking the Reynolds transport theorem.

https://en.wikipedia.org/wiki/Reynol...nsport_theorem

The basic physics is, you have a transport variable that moves around with the flow (advection in space-time). But as it moves around, it can also undergo some other physical processes (such as diffusion, or spontaneous reactions) and so on and so on.

It looks a lot like Navier-Stokes (which is a momentum transport equation) or the energy equation (which is an energy transport equation). The difference is that you have a different transport variable. In N-S it's momentum. In energy it's energy. In species transport, it is the species mass fraction (which is like a concentration).

The other difference is you need constitutive models to model any physical effects. In momentum transport you need something like a Newtonian/Stokes fluid. In energy transport, you need Fourier's law. In species transport, you need Fick's law to model the diffusion of species. Any chemical reactions show up as source terms in the species transport equation.

Thank you, sir.
But I need more information about species model because I will work on this model, so please suggest me to which book or notes are best for the understanding of this model of theory as well as setup procedure.
If you have any notes or book related to species model please send to me.
Thanks for advance.

[arulmechmb]

In species transport model, how to choose reaction types and turbulent chemistry interaction.
If anybody has notes related to this, Please share with me.
Thanks for advance.

[alnossory]

Hi everyone

I am trying to model evaporating of species using Fluent but the results I am getting are not logical specially the mass fraction.
I the model I have a container half of it filled with a mixture of two liquids (A and B). the mixture will evaporate by gaining heat from the surrounding. so the component A (from liquid phase) will evaporate first as its saturated temperature is lower than the component B.
The results I expect to get, the concentration of component B in the liquid mixture should be increased while vapour of the component A in the gas region should be increased. I could not get this results therefore i think there is something incorrect in the model.

can anyone help me to correct the mode or suggest an alternative way to model such problem?

Kind Regards
Abdalqader

[UmudM]

Hi everyone, I'm trying to analysis biogas reactor performance with different impeller types. But I need a help for mixing two liquid in a rector. In Fluent I have to make chemical reaction. In species transport model, how to choose reaction types and turbulent chemistry interaction.
If anybody has notes related to this, Please share with me.
Thanks for advance.
Thanks for attentions.
Kind Regards
Umud MUradov

[soumendu.dasgupta]

Hello everybody,

I am new to multiphase flow modeling in fluent and would like to simulate reactions between a gas and a liquid flowing cocurrently through a porous media. I have developed an understanding of porous media and relative permeability model. But do I need to enable species transport for this or is there any other way? My reaction is between diphenylbenzene (liquid) and hydrogen (gas). I would really appreciate if someone could kindly help me with this.

Thanks in advance.

[Kummi]

Hello Soumendu,
I haven't worked with multiphase flow modeling before. But for reactions inside porous medium, u need to enable species transport model --> Volumetric..

Thank you

[soumendu.dasgupta]

Originally Posted by Kummi

Hello Soumendu,
I haven't worked with multiphase flow modeling before. But for reactions inside porous medium, u need to enable species transport model --> Volumetric..

Thank you

Dear Kummi,

Thank you for your reply. I am not able to understand where to patch the rate equation udf inside the porous media section. Can you please help me?

Thanks

[soumendu.dasgupta]

Originally Posted by Kummi

Hello Soumendu,
I haven't worked with multiphase flow modeling before. But for reactions inside porous medium, u need to enable species transport model --> Volumetric..

Thank you

Thank you for your reply. I have the following reaction:

ArS(l) + H2(g) = Ar(l) + H2S(g)

1. Do I need to define both reactants and products in the species list?
2. How do I segregate between the liquid and gas. Because if I enable mixture template in the species transport model for both gas and liquid then both phases will have all the species components but I need the gas phase to contain only gas species and liquid phase to have only liquid species.

I would really be grateful if someone could kindly help me.

Thanks

[alialemana]

Hi,

did you solve this problem because I have the same problem!

Thanks

[alialemana]

Originally Posted by manoj.dundi

Good evening Cees sir,

I am using micro T channel for mixing two species. species A from one inlet and species B from other inlet. Both are having water properties.
inlet diffusion is selected under species transport. steady laminar flow model is used.

The solution is not converging for continuity for the above settings even when a residual of only 10^-03 is used for continuity.

Thanks and regards,
Manoj

Did you save this problem?
Thank you!