C	Concentration (kg·m−3)
D	Diffusion coefficient (m2·s−1)
di	Inner diameter of filler nanotube (nm)
do	Outer diameter of filler nanotube (nm)
J	Permeate flux (kg·m−2·s−1)
L	Length of nanotube filler (nm)
L 1	Size of the unit element in x-direction (nm)
L 2	Size of the unit element in y-direction (nm)
L 3	Size of the unit element in z-direction (nm)
M	Molecular weight (kg·kmol−1)
N	Number of nodes in simulation domain
n	Shape factor
P	Permeability (m2·s−1)
R	Gas constant (J·K−1·mol−1)
S	Solubility factor (g·m−3/g·m−3)
t	Time (s)
T	Temperature (K)
x	x coordinate
y	y coordinate
z	z coordinate
$\alpha$	Nanotube filler aspect ratio
$\theta$	Angle of filler orientation
$\psi$	Sphericity
φ	Volumetric filler content