Molecular spin in nano-confined fluidic flows

In this paper, we study the effect of molecular spin on the fluid dynamics of molecular nano-confined fluids using the extended Navier–Stokes equations. We show that the effect of spin is non-negligible for non-steady flows and we then discuss two examples, namely, a zero mean oscillatory flow and an oscillatory lid driven cavity flow. In the discussion of the former, we propose a dimensionless quantity that qualitatively predicts the effect of the spin. From this it is shown that only for sufficiently small system sizes and extremely high frequencies will molecular spin be relevant, depending on the molecular fluid’s rotational inertia and the rotational viscosity. In the lid driven cavity flow we observe that the thermodynamic energy dissipation due to molecular spin undergoes period doubling when increasing the Reynolds number and, under some circumstances, it may be negative.