Multicomponent diffusivities:
$ D_{kj} $
Mixture averaged diffusivities:
$ D_{km} = \dfrac{1-Y_k}{ \sum_{j \neq k}^{K} \dfrac{ X_j }{ \mathbb{D}_{jk} } } $
Binary diffusivities:
$ \mathbb{D}_{jk} $