Setup for fluid flow in Membrane Contactor with 2 fluids in counter current flow

liaa0811liaa0811 Member Posts: 5

Hello!

I kind of have a stupid question (maybe), but I couldn't find similar question or discussion in the forum. But really need to know about this to continue with my thesis research. Please help me~ Thank you!

So, I know how to do one component fluid flow simulation and modeling with modification of the baffles.

However, I have a difficulty in using 2 types of fluids that flow in counter current flow as attached in figure below:

(Source: https://doi.org/10.1016/S0376-7388(99)00040-X)

Is it possible to model 2 different fluids flowing in counter current flow ? Should I just make the track(components/solids in DM) of fluid1 and fluid2? but how can I model the interaction between these 2 fluids? like what kind of interfaces will happen and etc.

Or that means I have to combine VOF-multiphase + turbulence? or just use turbulence but with separate "fluids" geometry?


Thank you! Any help will be helpfull!!

Best Answers

  • RobRob UKPosts: 8,966Forum Coordinator
    Accepted Answer

    Yes, you can do this.

    The easy model is to consider both fluid passes separately, that's a good approach if you need to optimise flow distribution etc.

    As the two fluids don't mix you will have a wall separating the two passes. This allows heat but not mass transfer. To model the latter you'll need some UDF coding to remove (sink) and add (source) species based on whatever model you want to use. Note, the fluids are set via the Cell Zones, and this is not a multiphase model.

    A multiphase model would be where the two fluids interact, such as water & air in a river or sand & water in a pipe.

  • RobRob UKPosts: 8,966Forum Coordinator
    Accepted Answer

    Assuming the gas is only formed at the membrane I'd probably skip the multiphase model, but remember to account for any latent heat in the source terms. That also makes the UDF easier as there's no phase domain to account for, just the species.

  • RobRob UKPosts: 8,966Forum Coordinator
    Accepted Answer

    If you're switching from one channel to the other and the gas side is all ammonia vapour then no, but you will need two fluid materials. If the gas side has (for example) air in it then yes as gas side will be a species mixture.

Answers

  • liaa0811liaa0811 Posts: 22Member

    @Rob Alright! I got what you meant, so that means I have to start UDF coding learning to add source species. Do I also specify the mass transfer with certain reactions in UDF too?

    One more question, I am well aware multiphase model would be at least 2 different phases interact, but here in the membrane contactor the phase is like this:

    ammonium (liquid) -> ammonia (gas) *that pass through the hollow fiber membrane* -> this ammonia gas will be in spontaneous reaction with the fluid#2 and mixed together

    If that's the case, then I should combine multiphase (for the HF area part) but consider both fluid passes separately with UDF for mass transfer at the same time?? Like combining 2 concepts? If it's not right, please kindly explain.

    Thank you so much!!

  • liaa0811liaa0811 Posts: 22Member

    @Rob Oh! I think I got what you mean. I will try to do it first and learn UDF more! Thank you so much!!

  • RobRob UKPosts: 8,966Forum Coordinator

    @liaa0811 you're welcome. Have a careful read up on source terms, and then the UDFs. The hard part is going to be working out the rates, or rather what data is needed to calculate the mass transfer rate. Have a hunt around online for things like osmosis and membrane distillation as they're related to your application, but different enough you may not have thought about them.

  • liaa0811liaa0811 Posts: 22Member

    @Rob Sorry, I have a (maybe stupid) question here. So that means do I have to turn on the species model? since there will be 2 species here.. and to define mass fractions right?

  • liaa0811liaa0811 Posts: 22Member

    @Rob Oh! Alright. I got what you mean. Thank you! Should have studied harder on ANSYS basic :( Thank you!

  • RobRob UKPosts: 8,966Forum Coordinator

    @liaa0811 possibly; I do have a few years more experience than you at using the software!

  • liaa0811liaa0811 Posts: 22Member

    @Rob Hey! Sorry, I have a follow up question, let's say I already created separate 2 fluids model separately, and there will be 2 inlets and 2 outlets. Since I already created 2 fluids model (A & B), that means in the material part I will assign fluid A : sulfuric acid and fluid B:ammonia

    After that, I tried to input the velocity for inlet A : 1 m/s and inlet B: 1m/s. Does this means automatically only sulfuric acid will flow into inlet A, and only ammonia will flow into inlet B ?? *so like separate channels*

    Because I tried the exact thing as above, and I found it weird on the results (as if the velocity only affect one type of material) as the following:

    *streamlines*

    start from: inlet A (1)


    start from: inlet B (2)


    start from: fluid1 (which is supposed to be only ammonia)


    start from: porous-media (which is supposed to be only sulfuric acid)


  • RobRob UKPosts: 8,966Forum Coordinator

    That should be the case. You should also have walls separating the two channels so no material can pass between them. The faceting on the porous tubes looks really coarse so check you do have two distinct regions.

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