Suppose that I have a binary gas mixture at low pressure. Can I calculate the mean free path $\overline{\ell}$ of the gas molecule in a pores of solid material by substituting a molecular weight of a single component by Molecular weight of the binary mixture $M_{m,\rm mix}$ as well as the specific gas constant of this mixture $R_{\rm mix}$, such that I get:
\begin{equation} \overline{\ell} \:=\: \dfrac{3.2\cdot \mu_g}{p}\cdot \left(\dfrac{R_{\rm mix}\cdot T_{\rm abs}}{2\pi\cdot M_{m,\rm mix}}\right)\:\:\:\rm\left[m\right] \end{equation}
I am calculating $\overline{\ell}$ in order to determine the main diffusion mechanism in the pores (Bulk diffusion (Fick), Knudsen or its combination).