Filippos Sofos

Variation of Transport Properties Along Nanochannels: A Study by Non-equilibrium Molecular Dynamics

In the present work we calculate the transport properties of liquid argon for Poiseuille flow in a system confined by krypton walls using non-equilibrium molecular dynamics (NEMD) simulations where atoms interact via a Lennard-Jones potential. We examine the effect of channel width, system temperature and external force that drives the flow on diffusion coefficient, shear viscosity and thermal conductivity both as total average values for the whole channel, as well as local values across the channel. All transport properties are found to be significantly affected by the presence of the solid walls since their values in regions adjacent to the walls are different compared to those in layers near the channel centerline. In addition, for small channel widths where wall-fluid interaction affects most of the fluid region, transport properties present different behavior in comparison to bulk-like behavior. Following the nanoscale methodology described in the paper we can extract transport properties that can be used as input in macroscopic or multiscale simulations.

Darcy-Weisbach friction factor at the nanoscale: From atomistic calculations to continuum models

A modification of the Darcy-Weisbach friction factor applicable to nanoscale liquid transport processes is proposed. Non-equilibrium molecular dynamics simulations allow us to access the atomic behaviour of liquids moving in nanochannels, and by comparing atomistic simulation results with continuum Navier-Stokes solutions, we extend the applicability of continuum theory to nanoscale liquid flows. We find that classical continuum theory predictions of power dissipation do not apply in the case of nanochannels and have to be modified accordingly with input from atomistic simulations such as slip velocity and profiles of variable viscosity. The mathematical form of the friction factor expression persists for quite small nanochannel widths, i.e., the form of the relation for the friction factor f Re = const. is practically maintained even at the nanoscale, but the value of the constant significantly increases with increasing hydrophilicity.

Fluid structure and system dynamics in nanodevices for water desalination

AbstractNanofluidic applications are currently being investigated in use for water treatment systems as a power efficient and effective means of removing undesirable substances from drinking or sea water. A detailed study of liquid nanoflows, in both simulation and experimental systems, is a prerequisite for establishing the theory and guiding the technological research and development toward this direction. In this work, we investigate the implications introduced when downsizing a flow system at the nanoscale with molecular dynamics simulations. It is shown that the presence of the walls, hydrophobic or hydrophilic that interacts strongly with fluid particles, is the main effect on flow properties at the nanoscale, although this effect is neglected by the continuum theory that describes flows at macroscopic scale. Furthermore, we estimate the Darcy–Weisbach friction factor for nanoflows of this type.