Fluid mixtures in nanotubes

TL;DR

This paper models fluid mixtures in nanotubes using continuum mechanics, revealing that nanotubes can be filled with liquids or vapors and that flow rates can vastly exceed classical predictions, especially with vapor bulk.

Contribution

It introduces a continuum mechanics model for fluid mixtures in nanotubes based on mean-field molecular theory and density expansion, providing new insights into flow behaviors and component ratios.

Findings

Nanotubes can be filled with liquid or vapor mixtures depending on wall chemistry.

Flow rates in nanotubes can be several hundred thousand times larger than Poiseuille flow.

Carbon walls influence the fluid component ratios, favoring ethanol.

Abstract

The aim of the paper is the study of fluid mixtures in nanotubes by the methods of continuum mechanics. The model starts from a statistical distribution in mean-field molecular theory and uses a density expansion of Taylor series. We get a continuous expression of the volume free energy with density's spatial-derivatives limited at the second order. The nanotubes can be filled with liquid or vapor according to the chemical characteristics of the walls and of liquid or vapor mixture-bulks. An example of two-fluid mixture constituted of water and ethanol inside carbon nanotubes at 20{\textdegree} C is considered. When diameters are small enough, nanotubes are filled with liquid-mixture whatever are the liquid or vapor mixture-bulks. The carbon wall influences the ratio of the fluid components in favor of ethanol. The fluid-mixture flows across nanotubes can be much more important than classical ones and if the external bulk is vapor, the flow can be several hundred thousand times larger than Poiseuille flow.