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Old   June 21, 2009, 19:16
Default Diffusion UDF
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My simulation involves species diffusion in a porous bed. There is steady state velocity profile of solvent in the bed, with stagnant zones inside the pores of the solid phase (like an HPLC column). I solve for diffusion + convection in the fluid zone, while only for diffusion in the porous zone. I use the porous zone formulation to define the porous zone.

Do I need to define different diffusion coefficients in the fluid and porous zones? If so, how do write a UDF to define my diffusion coefficient in the porous zone?

How does Fluent calculate porous formulation? Say the porus zone is 65% porous. Does that mean Fluent automatically takes porous zone diffusivity as 65% of fluid zone diffusivity? What if the pores in the porous zone are tortuous? How do I include:
Diffusivity (porous zone) = [ 0.65 * Diffusivity (Fluid zone) ] / [ Tortuosity ]

Please advise.

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