Problem with multiphase flow - mixture model

Mat22 · October 21, 2010, 10:38

Hello guys,

I am actually trying to model the flow in a stirred tank filled by two fluids with different density but very close 1.072 and 1.1), my final goal is to estimate the time needed to homogeize the two liquids.
First, I calculated the steady flow in the tank with one fluid.
And I patched the second liquid in the tank where i wanted and I run an unsteady simulation solving only the volume fraction equation. (It is very similar to introduce a dyer in a converged flow fiield i think)
The problem is that there is absolutely no change in the distribution of the two phases. I guess it comes from the resolution of the volume fraction equation
If someone could help me with this, it would be very nice.

Thanks

Mat

thecfduser · October 25, 2010, 06:18

Hi
u must know that multiphase models do not account for mass diffusion of a liquid in another: the 2 phase are immiscible.

Tell me :
1-wich phase are u simulating first? the heavier or the lighter?
2-ure second phase, are u patching it on the top or on the bottom of the tank?
3-Wich multiphase modeling are u using?
4-Wich turbulence model?
5-Did u verify that ure flow is really unsteady?
6-Why dont u use lagrangian model ?

Mat22 · October 27, 2010, 03:07

Hi,

Thank you for answering my questions.
I called the fluent hotline after and I was told that the multiphase-mixture model is not wrong for my problem but is not the most appropriate, so, i changed to multi-species model, which works quite well.
I was also told that the mixture model is more for two phases where one is made of small spheres and so the model takes care of the drag and so on.

Mat

October 21, 2010, 10:38	Problem with multiphase flow - mixture model	#1
Mat22 New Member Mathieu Neuville Join Date: Aug 2010 Posts: 2 Rep Power: 0	Hello guys, I am actually trying to model the flow in a stirred tank filled by two fluids with different density but very close 1.072 and 1.1), my final goal is to estimate the time needed to homogeize the two liquids. First, I calculated the steady flow in the tank with one fluid. And I patched the second liquid in the tank where i wanted and I run an unsteady simulation solving only the volume fraction equation. (It is very similar to introduce a dyer in a converged flow fiield i think) The problem is that there is absolutely no change in the distribution of the two phases. I guess it comes from the resolution of the volume fraction equation If someone could help me with this, it would be very nice. Thanks Mat

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October 25, 2010, 06:18		#2
thecfduser Senior Member karine Join Date: Nov 2009 Posts: 158 Rep Power: 16	Hi u must know that multiphase models do not account for mass diffusion of a liquid in another: the 2 phase are immiscible. Tell me : 1-wich phase are u simulating first? the heavier or the lighter? 2-ure second phase, are u patching it on the top or on the bottom of the tank? 3-Wich multiphase modeling are u using? 4-Wich turbulence model? 5-Did u verify that ure flow is really unsteady? 6-Why dont u use lagrangian model ?

October 27, 2010, 03:07		#3
Mat22 New Member Mathieu Neuville Join Date: Aug 2010 Posts: 2 Rep Power: 0	Hi, Thank you for answering my questions. I called the fluent hotline after and I was told that the multiphase-mixture model is not wrong for my problem but is not the most appropriate, so, i changed to multi-species model, which works quite well. I was also told that the mixture model is more for two phases where one is made of small spheres and so the model takes care of the drag and so on. Mat