Methane Transport through Distorted Nanochannels: Surface Roughness Beats Tortuosity

Fluid transport through carbon nanotubes have shown remarkable flow properties, with measured flow rates orders of magnitude larger than the expected from standard continuum flow theories. Related studies have indicated that the observed high flow rates were driven by the extreme smoothness of the cylindrical nanotubes used in the experiments. In this work, we consider several types of nanochannels far from the cylindrical geometries. Using a combination of simulation techniques, such as molecular dynamics and the lattice Boltzmann method, we study the flow behavior under tortuous and rough channels, which are of fundamental relevance either for optimizing carbon nanotubes for nanofiltering applications, as well as for characterizing nanoporous organic media. We show that, although both features have a detrimental effect on flow rates, when nanochannels have both roughness and tortuosity simultaneously, shorter length-scales associated with surface roughness have a deeper impact, dominating the overall properties of the flow.