For the multicomponent option, the transport property evaluation follows the method described by Dixon-Lewis.[30] Multicomponent diffusion coefficients, thermal conductivities and thermal diffusion coefficients are computed through the solution of a system of equations involving the binary diffusion coefficients, the species mole fractions, and the thermodynamic and molecular properties of the species. Details of the matrix of equations, the solution algorithms, and the subsequent determination of multicomponent transport properties are provided in Gas-phase Species Transport Properties . These equations result in the determination of ordinary multicomponent diffusion coefficients, , for species diffusing in species , as well as species thermal diffusion coefficients and thermal conductivities.

For the multicomponent formulation, the correction velocity, , is not required and the diffusion velocity is defined as:

(13–11)

Now, the ordinary diffusion velocity term is given in Equation 13–12 .

(13–12)

Here is the mean molar mass, is the molar mass of species , and is defined as:

The thermal diffusion velocity is given as:

(13–13)

where is the thermal diffusion coefficient for species . We strongly recommend using the multicomponent option when thermal diffusion effects are important, as this is considerably more accurate than the mixture-averaged approach.