Learning Forum

[guan shengyi]

Hi all
I am trying to use an UDF to define mass diffusion coefficients for fluid in the system.
I am attempting to redefine the fluid diffusion coefficient using `DEFINE_DIFFUSIVITY`, but I am encountering issues. My goal is to modify the diffusion coefficient based on a pressure condition using a scaling factor, and I am using `C_DIFF_EFF(c,t,i)` to retrieve the diffusion coefficient. However, when storing this value in a User-Defined Memory (UDMI) variable, it remains 0. Can you help me identify the issue? Below is my UDF.
DEFINE_DIFFUSIVITY(DD, c, t,i)/*two-phase fluid*/
{
real Kg;/*diffusion coefficient*/

if (C_P(c, t) < 20e+05)
{
Kg = 10e-20*C_DIFF_EFF(c, t, 1);


}

else if (C_P(c, t) > 20e+05)
{
Kg = C_DIFF_EFF(c, t, 1);


}
C_UDMI(c, t, 0) = C_DIFF_EFF(c, t, 1);

return Kg;


}

[SRP]

Hi,

I suggest you to initialized kg to zero and try to store the modified kg in UDMI.

[Rob]

Duplicate /forum/forums/topic/define-mass-diffusion-coefficients-for-porous-media-and-multiphase/