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-   -   adsorption of moisture (http://www.cfd-online.com/Forums/fluent/36822-adsorption-moisture.html)

prasanth June 1, 2005 21:36

adsorption of moisture
 
hi,

what model would you suggest to simulate adsorption of moisture from air flowing through the silica-gel bed by the particles of the silica gel?

In multiphase model, we can specify these phases, but adsorption is a kind of reaction, hence i am thinking mass-tranfer in multiphase model wont do this.

will species transport model can do this?

awaiting an early response

us June 1, 2005 22:33

Re: adsorption of moisture
 
How about flow through porous media?

prasanth June 1, 2005 22:43

Re: adsorption of moisture
 
yeah, I too had thought about it. Actually, silica gel bed consists of small particles of silica gel. Also, how can we specify moisture being observed by silica gel.

Amir June 2, 2005 09:31

Re: adsorption of moisture
 
I have the same problem to solve but I haven't been able to get it converged yet :( First I tried to just solve for energy and species transport then I specified a porous media and solved for momentum and continuity too. It's been hard to get a realistic answer out of that. Still working on that though. I would be glad to hear what you guys come up with in this regards

Amir

Allan Walsh June 2, 2005 15:31

Re: adsorption of moisture
 

Allan Walsh June 2, 2005 19:13

Re: 2nd try adsorption of moisture
 
Hit the post message a bit too quickly last time.

Your options depend on how much time you want to spend and what sort of information you need.

If you just want mass loss, you could specify the absorbent region as porous cells and then go in and specify the region as a global sink for gas-phase H2O. Porous cells have the added benefit that you can set the parameters to give a representative pressure loss, if that is your intent.

Otherwise, you could add include some internal walls and have the absorption set to be a surface reaction (i.e water vapor to a hydrated form of the silica gel).

Or, you could set the gel region of your domain as porous cells and then write a UDF that does a better job of representing the physics of absorbtion (effects of surface area, velocity, temperature, etc.) For me, I would allocate at least a few weeks to write this kind of UDF. The previous approaches should require somewhat less time.

prasanth June 6, 2005 00:27

Re: 2nd try adsorption of moisture
 
hello Allan

thanks for your prompt reply and sorry for not replying immediately.

in your message: "If you just want mass loss, you could specify the absorbent region as porous cells and then go in and specify the region as a global sink for gas-phase H2O. Porous cells have the added benefit that you can set the parameters to give a representative pressure loss, if that is your intent."

our aim is to get that mass loss of h2o and air with reduced moisture comes out the unit. As u said, HOW TO SPECIFY THE POROUS CELL AS GLOBAL SINK FOR GAS-PHASE H20. looking for your reply

thanks prasanth

Allan Walsh June 6, 2005 13:30

Re: 2nd try adsorption of moisture
 
For global source/sink term, just click off the source box for the fluid region of interest and then go to the source tab and specify it. But, perhaps that really wasn't your question?

prasanth June 7, 2005 06:23

Re: 2nd try adsorption of moisture
 
hi alan

i know the optin of source term, infact i used for my earlier analysis. As you said, if we specify mass source, the mass transfer will be between air and water vapour. but we want the porous medium (silica gel) to absorb moisture from moist air.

Hope you understood my point and thanks for your kind response

prasanth

_Greg_ July 9, 2009 10:41

Hi,

If you want the porous media to adsorb moisture then i see 2 possibilites :

if you use a local equilibrium model for adsorption kinetic then the surface reaction capabilites of FLUENT could be enough.

if you use another kinetic model like Linear Driving Force to represent the mass transfer between column scale and macropores then you can use an UDF to modelize it. Then you will need to implement adsorption isotherms and add source terms on species transport, continuity and energy equations.


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