# Diffusion-coefficient based on mole fraction

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 November 9, 2006, 10:27 Diffusion-coefficient based on mole fraction #1 Fady Guest   Posts: n/a Sponsored Links 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); }

 November 11, 2006, 10:00 Re: Diffusion-coefficient based on mole fraction #2 Fady Guest   Posts: n/a no one got anythig...? it is quite important, and i have to get this working soon. thanks for the help

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