We investigated how the surface hierarchy of superhydrophobic (SHPo) surfaces influences liquid slip by testing well-defined microposts that have nanoposts only on their top. Contrary to the commonly held belief, our results show that such hierarchical surfaces do not always lead to an increase of slip length despite their reduced solid fraction and enhanced hydrophobicity compared to single-sc...

Internal recirculation in a moving droplet, enforced by the presence of fluid–fluid interfaces, plays an important role in several droplet-based microfluidic devices as it could enhance mixing, heat transfer, and chemical reaction. The effect of slip on droplet circulation is studied for two canonical steady-state problems: two-phase Couette, boundary-driven, and Poiseuille, pressure/body force...

Molecular dynamics simulations are carried out to investigate the dynamic behavior of the slip length in thin polymer films confined between atomically smooth thermal surfaces. For weak wall-fluid interactions, the shear rate dependence of the slip length acquires a distinct local minimum followed by a rapid growth at higher shear rates. With increasing fluid density, the position of the local ...

The shear rate dependence of the slip length in thin polymer films confined between atomically flat surfaces is investigated by molecular dynamics simulations. The polymer melt is described by the bead-spring model of linear flexible chains. We found that at low shear rates the velocity profiles acquire a pronounced curvature near the wall and the absolute value of the negative slip length is a...

Graetz and Nusselt studied heat transfer between a developed laminar fluid flow and a tube at constant wall temperature. Here, we extend the Graetz–Nusselt problem to dense fluid flows with partial wall slip. Its limits correspond to the classical problems for no-slip and no-shear flow. The amount of heat transfer is expressed by the local Nusselt number Nux, which is defined as the ratio of co...

With asymptotic and numerical analyses, we systematically study the influence of slip length and access Ohmic resistance (due to pore-end field focusing and concentration polarization) on the energy conversion efficiency of pressure-driven electrolyte flow through a charged nanopore. Hydrodynamic slip reduces the percent of energy dissipated by viscous dissipation but, through electro-osmotic c...

Effects of hydrophobic surface on skin-friction drag are investigated through direct numerical simulations of a turbulent channel flow. Hydrophobic surface is represented by a slip-boundary condition on the surface. When a slip-boundary condition is used in the streamwise direction, the skin-friction drag decreases and turbulence intensities and turbulence structures, near-wall streamwise vorti...

The aim of the present work is to analyze the accuracy and to extend the capability of lattice Boltzmann method in slip EOF; a phenomenon which was previously studied by molecular dynamics and less considered by LBM. At the present work, a numerical experiment on boundary conditions of slip velocity is performed and the proportionality of slip with shear stress in electroosmotic pump is proved....

In the context of numerical simulations of elastodynamic ruptures, we compare friction laws, including the linear slip-weakening (SW) law, the Dieterich-Ruina (DR) law, and the Free Volume (FV) law. The FV law is based on microscopic physics, incorporating Shear Transformation Zone (STZ) Theory which describes local, non-affine rearrangements within the granular fault gouge. A dynamic state var...