(168ab) Shear-Induced Radial Migration of Fluid Atoms In Pressure-Driven Single-Phase Flow

We report the results of large-scale molecular dynamics simulations of systems of liquid argon atoms in axial flows in circular conduits. We observe a migration of fluid atoms to the low-shear-rate region in the centre of the conduits. This migration leads to a large radial density gradient and a flattened velocity profile near the axis of symmetry in single-phase flow. We find that the extent of density gradient increases with the Péclect number. To the best of our knowledge, this atomic migration has never been reported in the literature before. At high Péclect numbers the observations in these molecular systems are in agreement with experiments and continuum level theory for concentrated suspensions of macroscopic particles. None of these results can be predicted by the solving Navier-Stokes and continuity equations for single-phase flow. The existence of large density gradient under conditions for which the flow is generally considered incompressible may have some fundamental implications on the incompressible flow assumption for people working to solve the Navier-Stokes equations for laminar flows in nanofluidic devices. Moreover, our findings have potential applications to demixing of different kinds of molecules and to pressure-driven laminar flows in micro- and nanofluidic devices, which operate under very high non-homogeneous shear rates.