[Moein Talebian]

Dear all,
There's a problem in static mixer simulation that any help and guidance of yours is appreciated
There's a Y-type static mixer which water enters one of the inlets and a mixture of water and ink (1 mol/m^3) enters the second
I wounder how I can calculate the concentration of ink on any cross sectional plane along the mixing channel in order to calculate the mixing quality.
And the other question is how can I specify the 1 mol/m^3 of ink in water.
This would solve a great problem of mine
Thanks in advance
Moein

[ghorrocks]

This simulation sounds like it should be a additional variable or multicomponent mixture simulation. If you have modelled this with multiphase models it would appear to be wrong.

If you put a plane on the cross section you want to measure you can calculate areaAve() of the mass fractions (or additional variable) to get the concentrations.

As for working out what 1 mol/m^3 is, you are going to have to work that out with the molar masses and densities. Mass fractions modelled in CFX are kg/m^3.

[Moein Talebian]

Originally Posted by ghorrocks

This simulation sounds like it should be a additional variable or multicomponent mixture simulation. If you have modelled this with multiphase models it would appear to be wrong.

If you put a plane on the cross section you want to measure you can calculate areaAve() of the mass fractions (or additional variable) to get the concentrations.

As for working out what 1 mol/m^3 is, you are going to have to work that out with the molar masses and densities. Mass fractions modelled in CFX are kg/m^3.

Dear Ghorrock,
Thanks for your reply
So should I figure out the features of water-ink combination beforehand and define it as a new fluid and then feed it to the system?

And other question would be:
Isn't mass fraction a non-dimensional parameter?
Shouldn't I look for something else?

Regards
Moein

[ghorrocks]

Have you done this simulation yet or are you trying to work out how to do it?

Yes, mass fraction is a non-dimensional number. I will let you derive how to get molar concentration from the mass fractions.

[Moein Talebian]

Originally Posted by ghorrocks

Have you done this simulation yet or are you trying to work out how to do it?

Yes, mass fraction is a non-dimensional number. I will let you derive how to get molar concentration from the mass fractions.

Yes. I simulated the same problem but with Acetone instead of water-ink mixture
I have also done it by the means of COMSOL multiphysics and my paper has been published lately.
I'm trying to substitute it with CFX due to finite volume nature of the solver.
Your help would probably be appreciated.

[ghorrocks]

OK, so what is your question? Do you want to know how to get the molar concentrations from the mass fractions?

[Moein Talebian]

Originally Posted by ghorrocks

OK, so what is your question? Do you want to know how to get the molar concentrations from the mass fractions?

There are actually two questions:
- How can I get molar concentration from the mass fraction?
- How can I define the mixing coefficient? (I couldn't find it in fluid definition module)

[ghorrocks]

1) Google it, if you can't derive it: https://en.wikipedia.org/wiki/Mass_fraction_(chemistry)

2) No idea. I suspect there are many ways to define mixing coefficient, so you have to choose the one suitable for your purpose.

[Moein Talebian]

Originally Posted by ghorrocks

1) Google it, if you can't derive it: https://en.wikipedia.org/wiki/Mass_fraction_(chemistry)

2) No idea. I suspect there are many ways to define mixing coefficient, so you have to choose the one suitable for your purpose.

Thanks an ocean for your guidance dear Ghorrock