Flow behavior and crystallization of supercritical carbon dioxide in nanochannels: Insights from molecular dynamics simulations

Abstract

This work investigates the flow behavior and crystallization of carbon dioxide (CO2) in a metallic nanochannel using coarse-grained molecular dynamics simulations. It is found that a high temperature decreases the flow velocity of CO2, and high-density zones can be formed inside the channel, inducing CO2 crystallization by shear flow that is accompanied by a rapid reduction of the potential energy of the system. Most of CO2 beads in the crystals exhibit an FCC structural distribution attributed to its easy-slip nature, while the others have an HCP structure. Moreover, the crystallization can be influenced by both CO2 density and surface roughness of nanochannels. It is demonstrated that a larger CO2 density can enhance the shear flow resistance and thus initiate the crystallization earlier, and surface roughness can extend the crystallization process but with a negligible effect on the equilibrium flow velocity. The above results have implications for designing and optimizing the nanofluidic systems for CO2 transport and storage.