We show by nonequilibrium molecular dynamics simulations that the Navier-Stokes equation does not correctly describe water flow in a nanoscale geometry. It is argued that this failure reflects the fact that the coupling between the intrinsic rotational and translational degrees of freedom becomes important for nanoflows. The coupling is correctly accounted for by the extended Navier-Stokes equations that include the intrinsic angular momentum as an independent hydrodynamic degree of freedom.
The authors acknowledge Lundbeckfonden for supporting this work as part Grant No. R49-A5634. The center for viscous liquid dynamics 'Glass and Time' is sponsored by the Danish National Research Foundation (DNRF).