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Old   September 30, 2009, 17:44
Default 2 diferent fluids mixing
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Felipe Gutiérrez Donoso
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I need to mix 2 diferent fluids (air-water) in a 3 way pipe (2 inlets, 1 outlet). I´ve activated the mixing model, but didn´t know how to define diferent fluids in the inlet boundary conditions.

Anyone knows how to do this??

Thanks in advance
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Old   September 30, 2009, 22:22
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define>species transport

u need to edit ur material u want to mix there.
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Old   October 1, 2009, 03:06
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Try to read more about mixture models.... in case of such kind of fluids may be better to use vof...
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Old   October 1, 2009, 03:09
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as i know u don't need vof if there is not reaction between 2 fluid.
Normal mixing is ok for just species transport.
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Old   October 1, 2009, 05:52
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As I said: Read more!!!!

The VOF model (described in Section 23.3) is a surface-tracking technique applied to a fixed Eulerian mesh. It is designed for two or more immiscible fluids where the position of the interface between the fluids is of interest. In the VOF model, a single set of momentum equations is shared by the fluids, and the volume fraction of each of the fluids in each computational cell is tracked throughout the domain. Applications of the VOF model include stratified flows , free-surface flows, filling, sloshing , the motion of large bubbles in a liquid, the motion of liquid after a dam break, the prediction of jet breakup (surface tension), and the steady or transient tracking of any liquid-gas interface.
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Old   October 1, 2009, 06:16
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Opps.. i didn't saw its a multiphase flow.
I have no experience in VOF model..
Philipov should be right.
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Old   October 1, 2009, 09:53
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I´ve thought about VOF, but I think that species model with low difusivity coefficient is better, because I´m using a 2 inlet pipe with one exit. Air must flow trough one inlet and water in the other.

I need an air injection, defining an air and a water inlet that i can´t find how to define separately with VOF.

Thanks
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Old   October 1, 2009, 10:00
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Have no comment to the question.... you really do not understand the physics of vof.... try to read the provided help files and you will find that in vof method (in case of 2 phases) you get primary and secondary... All that is 100% filled with one phase i 0% filled with the other one.. so you can define from one inlet water to be 1 volume fraction and air to be 0 (zero).. for the other inlet - define the opposite... out let define as outflow or pressure BC... whatever....
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Old   October 1, 2009, 10:03
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Quote:
Originally Posted by herntan View Post
as i know u don't need vof if there is not reaction between 2 fluid.
Normal mixing is ok for just species transport.
Surprised..... you say no reaction between 2 fluids - do not use vof!!!!!!!!!!!
Just the opposite.....
To all the people using this forum.... pay attention to the things you write.
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Old   October 1, 2009, 13:34
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Quote:
Originally Posted by Philipov View Post
so you can define from one inlet water to be 1 volume fraction and air to be 0 (zero).. for the other inlet - define the opposite...
that´s the question, I can´t find where to do that. Where did you found it??

I can´t define the Volume fraction at the inlet, because the Multiphase tab in BC menu doesn´t allow to define Volume fraction there.
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Old   October 1, 2009, 18:52
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maybe it´s a bug in FLuent 6.3.

I used VOF, but when I´m trying to define volume fraction at BC, the first time I click the second-phase tab, to set the second phase volume fraction, the Multiphase option doesn´t appear at all. I have to set all other BC FIRST before the multiphase tab appears in the second Phase.

The simulation converged fine and there wasn´t another problem.
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Old   October 1, 2009, 21:32
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haha.... i don't know what VOF all about.
but when goes for species transport with same phase... there is an difference on reaction and non reaction...

Philipov must be good in multiphase multi species. I would need ur help one day if i touch VOF or multiphase.
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Old   October 2, 2009, 03:24
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May be I was not clear... try to find vof tutorial...
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