Membrane Filtration CFD simulation

zobekenobe · May 14, 2018, 08:21

I am trying to simulate a 2 dimensional rectangular geometry using Fluent (with UDFs)

There is an inlet and outlet (opposite faces), the top surface is a wall and the membrane is on the bottom surface

I use a scalar transport equation for the solute. Using an analytic equation I calculate the flux through the membrane (bottom surface).
I have to apply the negative of the flux at the membrane surface and also have to calculate the concentration layer thickness on the membrane surface.

How do I define two conditions on the same boundary?

would defining the membrane surface as an inlet with a negative(outward) flux be of any sense?

is there an alternative approach?

I have tried using DEFINE_ADJUST to specify the negative flux at the membrane but FLUENT doesn't allow that.

I have tried using DEFINE_PROFILE by defining the membrane surface as a velocity inlet but then that leads reverse flow from the outlet and overprediction of the flux term through the membrane.

Any help would highly be appreciated even an alternative approach.

Thanks

Jimmyhanchn · June 1, 2018, 04:03

I am doing the same job with you, in my opinion, you want to calculate mass transfer coefficient on the membrane surface, right? I try to do the same simulation in CFX. I think you should select the model, film model, gel layer model, KS model and so on firstly. Today I still confused how to input concentration gradient in CCL and how to calculate boundary layer thickness. If you have some experience about that, share it plz.

zobekenobe · June 1, 2018, 08:02

Hi Jimmy,

Are these models available in CFX or do you implement them with CCLs.

I have been using FLUENT and have a ready UDF that I can share with you. I am referring to Ahmad et al. 2007. They are using a modified version of the spiegler kedem model.

I would like to find the apparent flux and the concentration layer for my problem. Apparently, I have the UDF ready and the equations too.

Could you please share the boundary conditions you have used, especially for the membrane surface.

Thanks

Jimmyhanchn · June 2, 2018, 01:20

I focused on mass transfer in one of unit cell by 3D simulation and periodic boundary setting. I try to realize film model in the empty channel firstly. Of course, CFX cannot apply this model directly. So that is why I have to try to input equations in CCL. But today I still confused how to calculate concentration gradient. For you, I think in 2D model you have to take the thickness of boundary layer into consideration. It is not a constant! I don't know the publication you mentioned, Can you give its full name? Fluent is so difficult to me, do you have some experience with CFX? Can you tell me how to input differential equation in CCL?

Jimmyhanchn · June 3, 2018, 01:21

what kind of solution did you use, salt? I have a question, Do you know what the difference between setting flow as salt flow or setting a source subdomain in concentration simulation?

zobekenobe · June 5, 2018, 12:40

Hi Jimmy,

I am trying to simulate the following paper ahmad et al. 2005

Sorry but I'm not experienced with the CCL style programming of CFX. However the general strategy I have seen so far with FLUENT and OpenFOAM to solving the concentration polarization equations is to solve the transport equation for solute (scalar) mass and use the 2 film boudary model as in the paper to estimate the thickness layer.

In the follow up paper the authors account for a dynamic value of flux through the membrane.

May 14, 2018, 08:21	Membrane Filtration CFD simulation	#1
zobekenobe Member zobekenobe Join Date: Mar 2009 Location: Dublin, Ireland Posts: 72 Rep Power: 17	I am trying to simulate a 2 dimensional rectangular geometry using Fluent (with UDFs) There is an inlet and outlet (opposite faces), the top surface is a wall and the membrane is on the bottom surface I use a scalar transport equation for the solute. Using an analytic equation I calculate the flux through the membrane (bottom surface). I have to apply the negative of the flux at the membrane surface and also have to calculate the concentration layer thickness on the membrane surface. How do I define two conditions on the same boundary? would defining the membrane surface as an inlet with a negative(outward) flux be of any sense? is there an alternative approach? I have tried using DEFINE_ADJUST to specify the negative flux at the membrane but FLUENT doesn't allow that. I have tried using DEFINE_PROFILE by defining the membrane surface as a velocity inlet but then that leads reverse flow from the outlet and overprediction of the flux term through the membrane. Any help would highly be appreciated even an alternative approach. Thanks

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June 1, 2018, 04:03		#2
Jimmyhanchn Member Jimmy Join Date: Sep 2016 Location: Japan Posts: 38 Rep Power: 9	I am doing the same job with you, in my opinion, you want to calculate mass transfer coefficient on the membrane surface, right? I try to do the same simulation in CFX. I think you should select the model, film model, gel layer model, KS model and so on firstly. Today I still confused how to input concentration gradient in CCL and how to calculate boundary layer thickness. If you have some experience about that, share it plz.

June 1, 2018, 08:02		#3
zobekenobe Member zobekenobe Join Date: Mar 2009 Location: Dublin, Ireland Posts: 72 Rep Power: 17	Hi Jimmy, Are these models available in CFX or do you implement them with CCLs. I have been using FLUENT and have a ready UDF that I can share with you. I am referring to Ahmad et al. 2007. They are using a modified version of the spiegler kedem model. I would like to find the apparent flux and the concentration layer for my problem. Apparently, I have the UDF ready and the equations too. Could you please share the boundary conditions you have used, especially for the membrane surface. Thanks

June 2, 2018, 01:20		#4
Jimmyhanchn Member Jimmy Join Date: Sep 2016 Location: Japan Posts: 38 Rep Power: 9	I focused on mass transfer in one of unit cell by 3D simulation and periodic boundary setting. I try to realize film model in the empty channel firstly. Of course, CFX cannot apply this model directly. So that is why I have to try to input equations in CCL. But today I still confused how to calculate concentration gradient. For you, I think in 2D model you have to take the thickness of boundary layer into consideration. It is not a constant! I don't know the publication you mentioned, Can you give its full name? Fluent is so difficult to me, do you have some experience with CFX? Can you tell me how to input differential equation in CCL?

June 3, 2018, 01:21		#5
Jimmyhanchn Member Jimmy Join Date: Sep 2016 Location: Japan Posts: 38 Rep Power: 9	what kind of solution did you use, salt? I have a question, Do you know what the difference between setting flow as salt flow or setting a source subdomain in concentration simulation?

June 5, 2018, 12:40		#6
zobekenobe Member zobekenobe Join Date: Mar 2009 Location: Dublin, Ireland Posts: 72 Rep Power: 17	Hi Jimmy, I am trying to simulate the following paper ahmad et al. 2005 Sorry but I'm not experienced with the CCL style programming of CFX. However the general strategy I have seen so far with FLUENT and OpenFOAM to solving the concentration polarization equations is to solve the transport equation for solute (scalar) mass and use the 2 film boudary model as in the paper to estimate the thickness layer. In the follow up paper the authors account for a dynamic value of flux through the membrane.