The effects of roughness and width on transport characteristics of methane in nanopores

This study presents the effects of nanopore surface roughness on the transport characteristics of methane by considering nanopore width dependence using the non-equilibrium multiscale molecular dynamic simulations. Results show a monotone increasing quasi-parabolic relationship between the mass transfer coefficient and the width of nanopore with different surface roughness levels, while the shear viscosity shows the opposite pattern of change. Moreover, in the middle of fluid domains, the shear viscosity slightly decreases (diffusivity increase) with the increase in the nanopore roughness amplitude at the given rough wavelength, an opposite trend is observed nearby the nanopore surface. For the selected rough amplitude and the same nanopore width, we find that the diffusion coefficient is the smallest for λ2=4.31σ. The shear viscosity is also the smallest in the center of nanopore for λ2=4.31σ, while it i's the biggest in the fluid domain nearby the nanopore surface. Furthermore, the diffusion coefficient and the shear viscosity approximate to the bulk system when the nanopore width h>4.968nm. In addition, the results of the C (H) atom number densities, velocities distributions, boundary slip velocity, velocity autocorrelation functions, mean force potential, and the escape rate display significant differences, which unanimously indicate that the nanopore width and surface roughness significantly influence the transport characteristics of methane nanofluidics. These numerical results are highly valuable for the design of micro and nano-devices.