How to model the separation of oil from water, using Ansys CFX?

Ashkan Kashani · April 6, 2016, 16:37

Hi everyone
I am trying to model separation of oil from water by means of textures. I want to use Ansys CFX. I know that I should model the texture as a porous media but I don't know how can I model the absorption of oil since the porous model just added some extra pressure drop terms (i.e. Darcy–Forchheimer law) to momentum equation and there is not any real physical media to absorb the oil

.
Any suggestion or advise is much appreciated since i'm frustrated. Thanks guys in advance.

ghorrocks · April 6, 2016, 20:02

What scale do you wish to model this effect?

If you want to model the microscale, that is a physical model to directly model where the oil gets stuck in the material and the water flow around it - then you will need to model the material as labyrinth passages and a free surface model for water/oil.

If you want to model the global scale, that is oil/water goes in and only water comes out and you are not too concerned about the microscopic details - then you have a few options:
* If you use a momentum source term I think you can put different terms per phase. Then you can have a bigger resistance to flow for oil than water.
* You can use a mass source term to just make the oil disappear at a controlled rate.

Ashkan Kashani · April 7, 2016, 12:26

Hi

I'm so grateful for your reply

Actually I'm not interested in microscopic details. My aim is just to evaluate the absorption capacity of different porous materials.

I would ask how should I calculate the mentioned sources and introduce them to CFX solver?

ghorrocks · April 7, 2016, 19:18

Isn't the different absorption capacity of different materials dependent on the microscopic details? Then you have to do the microscopic model.

What sort of characteristics are different in the materials you are assessing? How different do you expect the absorption to be?

And probably the most important question: This is starting to sound like something which will be difficult to do well using CFD, but would be far more easily tested experimentally. So why do the CFD at all?

April 6, 2016, 16:37	How to model the separation of oil from water, using Ansys CFX?	#1
Ashkan Kashani Member Ashkan Kashani Join Date: Apr 2016 Posts: 46 Rep Power: 10	Hi everyone I am trying to model separation of oil from water by means of textures. I want to use Ansys CFX. I know that I should model the texture as a porous media but I don't know how can I model the absorption of oil since the porous model just added some extra pressure drop terms (i.e. Darcy–Forchheimer law) to momentum equation and there is not any real physical media to absorb the oil . Any suggestion or advise is much appreciated since i'm frustrated. Thanks guys in advance.

April 6, 2016, 20:02		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	What scale do you wish to model this effect? If you want to model the microscale, that is a physical model to directly model where the oil gets stuck in the material and the water flow around it - then you will need to model the material as labyrinth passages and a free surface model for water/oil. If you want to model the global scale, that is oil/water goes in and only water comes out and you are not too concerned about the microscopic details - then you have a few options: * If you use a momentum source term I think you can put different terms per phase. Then you can have a bigger resistance to flow for oil than water. * You can use a mass source term to just make the oil disappear at a controlled rate. Ashkan Kashani likes this.

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April 7, 2016, 12:26		#3
Ashkan Kashani Member Ashkan Kashani Join Date: Apr 2016 Posts: 46 Rep Power: 10	Hi I'm so grateful for your reply Actually I'm not interested in microscopic details. My aim is just to evaluate the absorption capacity of different porous materials. I would ask how should I calculate the mentioned sources and introduce them to CFX solver?

April 7, 2016, 19:18		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Isn't the different absorption capacity of different materials dependent on the microscopic details? Then you have to do the microscopic model. What sort of characteristics are different in the materials you are assessing? How different do you expect the absorption to be? And probably the most important question: This is starting to sound like something which will be difficult to do well using CFD, but would be far more easily tested experimentally. So why do the CFD at all?