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Ways to find Mass transfer coefficient using CFD?

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Old   August 11, 2010, 01:51
Question Ways to find Mass transfer coefficient using CFD?
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tukaram
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What are ways to find Mass transfer coefficient (MTC) using CFD? Example, Gas species A gets dissolved into liquid solution (i.e. transfer of A from gas mixture to liquid solution).
  • If species A gets transfered from Gas to liquid through interface, what are the ways to find mass transfer coefficient using hydrodynamics data from CFD?
  • Can we define diffusivity of species in both gas phase and liquid phase and predict concentration gradients? Either in CFX or FLUENT.
Has any body used CFD for predicting MTC like it's used to find heat transfer coefficient (HTC)?

Please reply.

Thanks!
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Old   August 11, 2010, 06:25
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Glenn Horrocks
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First question - no.
Second question - yes.

But a major factor in mass transfer is the interface condition, that is the jump from gas to liquid. You really need empirical data or a firm knowledge of the underlying physics to do this accurately.
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Old   August 11, 2010, 07:49
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Glenn,
Thanks for quick reply.
Second question: What if I have relationship between concentrations of species A at interface? That is equilibrium relationship between concentration in gas phase and liquid phase. [Example, Henry's constant. C_intf_gas = H_constant *C_intf_liquid].

Can I use such relationship and predict concentration profiles of A due to diffusive mass transfer from gas to liquid solution?

Thanks!
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Old   August 11, 2010, 08:01
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Glenn,
Thanks for quick reply to my post on cfd forum.
I agree with you, we need to know relationship of species concentrations between gas phase and liquid phase.
What if I assume the relationship is known like equilibrium relationship?
C_intf_gas = Eqbm_constant *C_intf_liquid.

Can I use this relationship along with diffusivity in both phase and predict concentration profiles of A?
If you have any document or sample solved using CFX/ FLUENT, please share with me, if permitted.

Thanks!
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Old   August 11, 2010, 08:03
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Yes, but only for equilibrium conditions. This means any transients need to be slow enough to be treated as equilibrium.
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Old   August 11, 2010, 08:16
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Well appreciated, the system dynamics should be slow enough for gas-liquid bulks to be in equilibrium.
But I have situation where gas and liquid bulks are not at equlibrium but equilbrium exists at interface.

Hence some clarification needed on how Henry's Law is used in interface mass transfer of CFX?

Henry's Law gives relationship between concentration of species in gas phase in euqilibrium with concentration in bulk liquid phase.

C_eqbm_gas = H_constant* C_bulk_liquid.

Thanks.
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Old   August 11, 2010, 18:47
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I have never modelling this type of thing. A search of the documentation for "Henry" found details of its implementation in CFX. You have better start reading.
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Old   August 15, 2010, 23:16
Default Ways to find Mass transfer coefficient using CFD?
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Thanks,
Glenn. I will try the option of Henry's constant. Please extend your help for any queries regarding mass transfer in CFX.

Regards
Tuks
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Old   August 16, 2010, 13:15
Default Diffusion coefficient
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Neil Duffy
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Hi,

My question is somewhat similar. I am looking to pull the mass diffusion coefficient from the solver and implement it into a UDF. Basically, I want to simulate the drying of a solid biomass particle in a furnace. To do this I need to find the mass transfer coeffiect which depends on the diffusion coefficient between the solid and gas phase. I also want to use the diffusion coefficient for char oxidation (to determine the mass transfer of oxygen to the solid).

As CFX uses the diffusion coefficient for many in built models, is there a way to extract it?

Any help would be greatly appreciated.

Cheers,

Neil
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Old   August 16, 2010, 18:19
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You will probably be able to do this in CEL, so no need for a user fortran routine. UDF is fluent-speak anyway.
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Old   April 15, 2011, 11:20
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Hi guys, I am not sure if this is the right place to ask, anyway here's my question:
what is exactly the difference between the 'particle transport fluid' option and the 'droplet(phase change)' one?
I saw that the second one activates the mass transfer keyword, is this it?
I thought that maybe the particle transport fluid model simply solves particles equations, but without accounting for their evaporation (and consequent diameter variation).

Thanks in advance

Marta
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