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is it possible to define different mass diffusion coefficients in different zones?

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Old   June 3, 2019, 20:24
Default is it possible to define different mass diffusion coefficients in different zones?
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Weiqiang Liu
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Hi all,

I am trying to define an effective mass diffusion coefficient in porous zone while the other fluid zone has mass diffusion coefficient calculated by kinetic theory.

L-J parameters are imported for every species to calculate binary diffusion coefficient and then mixture averaged or multi-component diffusion coefficients are calculated according to model utilized.

In the porous zone, the mass diffusion coefficient is a function of both molecular diffusion coefficient and knudsen diffusion coefficient. In other words, in non-porous zone, diffusion coefficients for every species are calculated by kinetic theory while in porous zone, diffusion coefficients for every species are a combination of molecular diffusion(kinetic theory) and knudsen diffusion coefficient. I wonder is this doable in fluent? I put my UDF code below though it can not be loaded with some errors.

Can anybody help me to check the code whether the logic and syntax is right?

#include "udf.h"
DEFINE_DIFFUSIVITY(mass_diff,c,t,i)
{
double dpore=20e-9;
double gasconstant=8.314;
double Dknudsen;
double T=300.0;
double pi=3.14;
double tortuosity=3.0;
double porosity=0.5;
double Deffective;
double Dmolecular;
int isp;
real mw;
Domain *domain;
Material *mix_mat,*sp;
domain=Get_Domain(1);
mix_mat=mixture_material(domain);
mixture_species_loop(mix_mat,sp,isp)
{
if(isp==i)
{
mw=MATERIAL_PROP(sp,PROP_mwi);
}
}
T=C_T(c,t);
Dmolecular=C_DIFF_EFF(c,t,i);
Dknudsen=dpore/3*sqrt(8*gasconstant*T/(pi*mw))
if(THREAD_ID(t)==ZONE_17)
Deffective=porosity/tortuosity*(1/(1/Dmolecular+1/Dknudsen));
else if(THREAD_ID(t)==ZONE_16)
Deffective=Dmolecular;
return Deffective;
}
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