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-   -   Which model should I choose? (http://www.cfd-online.com/Forums/openfoam/118879-model-should-i-choose.html)

sharonyue June 5, 2013 19:50

Which model should I choose?
 
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Hi All,

Recently I am uncertain which model I should use in my project. Its a gas-liquid mixing system, but the liquid is xanthan gum. When gas is injected into xanthan gum. the flow type is kind like slug flow. Look the image 3, So there are many fine bubbles and some big gas slugs. Until now I am willing to choose VOF or Euler-Euler model.

1. Regarding VOF, as of the mesh reason, in the simulation there would not have this fine bubbles. but I can have this big gas slugs.

2. Reagrding Euler-Euler model, I am not sure what the reault looks like. I only made a test about air-water system. But I heard two fluid model cannot deal with seperation rite?

Any ideas ?


BTY, in experiment, which method do you use if you want to get global gas hold up or local bubble size? Now I am using expansion technique. But the liquid level fluctuate woo much which affect my global gas hold up badly.

Thanks in advance.

oj.bulmer June 6, 2013 05:40

VOF seems a strong contender. Since the the bubbles are of really large size having a distinct interface. But be aware that you will need a very fine mesh if you want to capture the interface.

Quote:

Reagrding Euler-Euler model, I am not sure what the reault looks like. I only made a test about air-water system. But I heard two fluid model cannot deal with seperation rite?
Euler model is great for dispersed bubbles and the additional population models can also model the coalescence and breakup. But I don't think you are look for this.

I was wondering, if this is a tank, do you specify the top surface as free surface or degassing boundary condition (using UDF)?

OJ

sharonyue June 6, 2013 23:36

Quote:

Originally Posted by oj.bulmer (Post 432384)
VOF seems a strong contender. Since the the bubbles are of really large size having a distinct interface. But be aware that you will need a very fine mesh if you want to capture the interface.



Euler model is great for dispersed bubbles and the additional population models can also model the coalescence and breakup. But I don't think you are look for this.

I was wondering, if this is a tank, do you specify the top surface as free surface or degassing boundary condition (using UDF)?

OJ

Hi OJ,

I am using OpenFOAM, I dont need to specify the gas-liquid interface's B.C. in the tank's outlet, I make U's zerogradient and pressure is fixedvalue. so in FLUENT I am not quite familiar with that, Sorry about that.

In OpenFOAM, there is no PBM, so I have to implent it by myself which its very tough for me.

Regarding VOF, Have you ever made a test to see the viscosity field? I have some of this unnormal viscosity problems...In OpenFOAM, if the liquid's viscosity is changing (non-newtonian fluid), all of the viscosity include the air's is the same. I dont know if this exists in FLUENT?

Thanks for your reply.

oj.bulmer June 7, 2013 06:52

I see, I think you are on the wrong forum then. Try posting it on OPENFoam forum?

OJ


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