Mass Transfer UDF using Fluent VOF
 

Hello, I am studying the air bubble dynamics from a submerged orifice in pool of aqueous soln of surfactants. As surfactant molecules adsorb and desorb on the moving bubble interface, I need to put a concentration boundary condn on the moving interface. (need to specify a specific concentration function on the bubble interface). As I am using VOF module in Fluent 12, my question is, can I specify a concentration BC on the moving bubble interface? How do I limit my concetration BC equation to region where volume fraction is between 0 to 1? Can I write a UDF for the same?

If your interface is actually defined by the fluid flow (it's arbitrarily deformable), you'll need to write a udf which loops over cells, determines the interface (C_VOF !=0 && C_VOF!=1), and then sets the mass fraction of the surfactants at the interface. While it's a phase interface, it's not really a boundary condition in the Fluent sense.

ComputerGuy

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@Computer Guy

Thank you very much for your reply.
I am still working on it. I might have more questions for you later. :P

But thank you very much for your prompt reply.

~
Anirudh

Hi,

This seems to be an old thread, but I will try anyway...

I am also working in my UDF to define mass transfer between 2phases. I need a transitory mass transfer, it is to said, the mass transfer between phases varies with time.

I know how to define a mass transfer in this sense. The question is I am not sure if the value I am sending to the mass transfer is correct. I have available a curve that measures concentration of a substance (ppm) with time, so, for example, at t=1 I have 24ppm of phase 2, at t=2 I get 20 ppm of phase 2 and so on.

I guess if I impose directly this values (fitted in a time-dependent curve) in my UDF I will be doing it wrong. I fairly remember I have read somewhere that you are specifying kg/m3/s.

Could any UDF expert seed some light on this issue?

Thank you in advance.

Regards,

Tensi