CFD Online Discussion Forums

CFD Online Discussion Forums (
-   CFX (
-   -   porous filtration membrane area in model (

catherina March 30, 2007 09:53

porous filtration membrane area in model
Dear all,

I am currently working on a filtration model and I am simulating the flow along the two sides of the membrane and the flow inside the membrane. My membrane is hydrophobic and the current available CFX porous model does not take hydrophobicity or contact angles into account. Additionally it uses Darcy's equation while I need to use a set of different equations. I have the equations available, but I would very much appreciate some input from you on how to incorporate them into the model. I am fairly confident with FORTRAN so that would not be a problem. However I would like to know 1. How can I incorporate the external equations? Do I run them from a user subroutine as an option available in Pre? 2. For my membrane area I have chosen a 2-D mesh and would like to take each node as a pore (hence solving the equation there). Would that be at all possible? 3. Is it better if I was to use "porous" in the domain selection and put the extra equations or keep it as "fluid" and add what is needed? Any ideas would be more than welcome Many thanks in advance


opaque March 30, 2007 12:12

Re: porous filtration membrane area in model
Dear Catherina,

How would you model the hydrophobic behavior? Something along the lines of reflection coefficients (Staverman's)?

CFX does not use Darcy's equation? Where did you read that? The current porous model includes linear and quadratic resistance coefficients; therefore, it follows into the Darcy-Forcheimer models. It also includes viscous diffusion effects which will put them into the Brinkman type of models. In addition, it also includes advection.. What model are you planning to use?

1 - If by external equations you mean solving additional equations.. Please see doc about Additional Variables.

If you mean adding additional terms to the equations, please see doc about Sources (either volumetric or boundary) into the different equations.

2 - Do you plan to solve the equation on the surface of the membrane with solution values different from those on both sides of the domain? I do not believe that is possible. You should probably extrude the mesh one element, and solve an additional variable as a solid domain.

3 - Not knowing your equations, it is not easy to say.


catherina March 30, 2007 13:01

Re: porous filtration membrane area in model
Dear Opaque

Many thanks for your answer. CFX does use Darcy I know that but what I was wondering is whether (since I don't need to use Darcy) I could dismiss the available porous models completely and add my own equations (which I think is possible via the additional variables). The other thing regarding solving the membrane equations on a grid I think is quite difficult and then there is the evaporation and condesation on the membrane surface but ... I will post my equations on the forum in the next few days.

Kind regards


vittal October 27, 2011 06:05

porous model parameters
Hi any one tell me how to calculate permeability when velocity,porosity and thickness of the porous medium is known.
I am using discrete phase model.
Velocity is 5.6 m/s
water vapor and liquid droplets of 0.3 mm
pressure is 5690 pa
porous medium thickness 0.15mm

All times are GMT -4. The time now is 03:02.