DEPARTURE FROM NAVIER-STOKES HYDRODYNAMICS IN CONFINED LIQUIDS

In this work we use nonequilibrium molecular dynamics (NEMD) to simula te an atomic liquid undergoing gravity-fed flow down a narrow channel. We compare the simulation results against the predictions of classica l Navier-Stokes theory for two different channel widths. For a channel width of 5.1 molecular diameters, we find that the velocity profile d eviates significantly from the hydrodynamic prediction. The shape of t his velocity profile is found to be independent of the applied field ( pressure gradient). We find that the heat flux profile does not agree with the cubic profile predicted, by Navier-Stokes hydrodynamics, but shows significant oscillations located about one molecular diameter fr om the walls. This result differs from the earlier work of Todd and Ev ans [B. D. Todd and D. J. Evans, J. Chem. Phys. 103, 9804 (1995)], in which an assumption of a purely quadratic velocity profile resulted in very weak oscillations in the heat flux. We fmd that in narrow channe ls the viscosity cannot be described by a linear, local constitutive r elation. However, classical Navier-Stokes behavior is approached for a channel width of >similar to 10 molecular diameters.