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Diffusion-coefficient based on mole fraction

Hello,

i want to write an UDF that defines my diffusion coefficient dependend on the mole fraction. Because there is no mole fraction macro i have to calculate it by my own. So i used the Molecular-Weight of the Molecules and the Mass Fraction to calculate the mole fraction. But something is still going wrong, i get an error when i want to interrate my Diffusionmodel. The file gets compiled and everything. anyone got an idea? thanks for the help

#include "udf.h"

DEFINE_DIFFUSIVITY(diffcoef, c, t, i) {

double M_ETH = 88.11; // [kg/kmol]

double M_CYC = 84.16; // [kg/kmol] double mass; // [kg]

double n_ETH; // [kmol]

double n_CYC; // [kmol]

double n_frac_ETH; // [-]

mass = C_R(c,t) * C_VOLUME(c,t);

n_CYC = C_YI(c,t,2) * mass / M_CYC;

n_ETH = C_YI(c,t,1) * mass / M_ETH;

n_frac_ETH = n_ETH / (n_ETH + n_CYC);

return 0.0833*pow(10,-7) * pow(n_frac_ETH,4)

- 0.1625*pow(10,-7) * pow(n_frac_ETH,3)

+ 0.1367*pow(10,-7)* pow(n_frac_ETH,2)

- 0.0494*pow(10,-7) * n_frac_ETH

+ 0.0184*pow(10,-7);

}