Poiseuille flow of Lennard-Jones fluids in narrow slit pores

Abstract

We present results from nonequilibrium molecular dynamics (NEMD) simulations of simple fluids undergoing planar Poiseuille flow in a slit pore only a few molecular diameters in width. The calculations reported in this publication build on previous results by including the effects of attractive forces and studying the flow at narrower pore widths. Our aims are: (1) to examine the role of attractive forces in determining hydrodynamic properties, (2) to provide clearer evidence for the existence of a non-Markovian generalization of Newtons law, (3) to examine the slip-stick boundary conditions in more detail by using a high spatial resolution of the streaming velocity profiles, (4) to investigate the significance of the recently proposed cross-coupling coefficient on the temperature profiles. The presence of attractive interactions gives rise to interesting packing effects, but otherwise, does not significantly alter the spatial dependence of hydrodynamic quantities. We find the strongest evidence to date that Newton’s Law breaks down for very narrow pores; the shear viscosity exhibits singularities. We suggest a method to test the validity of the non-Markovian generalization of Newton’s Law. No-slip boundary conditions are found to apply, even at these microscopic length scales, provided one takes into account the finite size of the wall atoms. The effects of any strain rate induced coupling to the heat flow are found to be insignificant.