Autonomous Sensors Powered by Energy Harvesting from von Karman Vortices in Airflow.

In this paper an energy harvesting system based on a piezoelectric converter to extract energy from airflow and use it to power battery-less sensors is presented. The converter is embedded as a part of a flexure beam that is put into vibrations by von Karman vortices detached from a bluff body placed upstream. The vortex street has been investigated by Computational Fluid Dynamics (CFD) simulations, aiming at assessing the vortex shedding frequency as a function of the flow velocity.

Algorithm to enforce uniform density in liquid atomistic subdomains with specular boundaries.

An important component in hybrid atomistic-continuum (HAC) modeling of liquids is the proper termination of the atomistic subdomain (ΩA). When the HAC model is based on the Schwarz domain decomposition method, the total number of particles in ΩA is conserved using specular boundaries in an overlap region, where information is exchanged with the continuum subdomain (ΩC). This non-periodic termination of ΩA fails to account for forces otherwise included in a periodic system, through the minimum image convention.

Mechanisms of molecular permeation through nanoporous graphene membranes.

We present an investigation of molecular permeation of gases through nanoporous graphene membranes via molecular dynamics simulations; four different gases are investigated, namely helium, hydrogen, nitrogen, and methane. We show that in addition to the direct (gas-kinetic) flux of molecules crossing from the bulk phase on one side of the graphene to the bulk phase on the other side, for gases that adsorb onto the graphene, significant contribution to the flux across the membrane comes from a surface mechanism by which molecules cross after being adsorbed onto the graphene surface. Our results quantify the relative contribution of the bulk and surface mechanisms and show that the direct flux can be described reasonably accurately using kinetic theory, provided the latter is appropriately modified assuming steric molecule-pore interactions, with gas molecules behaving as hard spheres of known kinetic diameters.

Dissolution of a liquid microdroplet in a nonideal liquid-liquid mixture far from thermodynamic equilibrium.

A droplet placed in a liquid-liquid solution is expected to grow, or shrink, in time as approximately t;{1/2}. In this Letter, we report experimental evidence that when the composition in the interface is far from thermodynamic equilibrium due to the nonideality of the mixture, a droplet shrinks as approximately t. This scaling is due to the coupling between mass and momentum transfer known as Korteweg forces as a result of which the droplet self-propels around.

Evidence of convective heat transfer enhancement induced by spinodal decomposition.

Spinodal decomposition can be driven by either diffusion or self-induced convection; the importance of convection relative to diffusion depends on the Péclet number, defined as the ratio between convective and diffusive mass fluxes. Diffusion is the dominating mechanism of phase segregation when the Péclet number is small - i.e.

Effects of quenching rate and viscosity on spinodal decomposition.

Spinodal decomposition of deeply quenched mixtures is studied experimentally, with particular emphasis on the domain growth rate during the late stage of coarsening. We provide some experimental evidence that at high Péclet number, the process is isotropic and the domain growth is linear in time, even at finite quenching rates. In fact, the quenching rate appears to influence the magnitude of the growth rate, but not its scaling law.

Stationary core-annular flow through a horizontal pipe.

A theoretical investigation has been made of core-annular flow: the flow of a high-viscosity liquid core surrounded by a low-viscosity annular liquid layer through a horizontal pipe. Special attention is paid to the question how the buoyancy force on the core, caused by a possible density difference between the core and the annular layer, is counterbalanced. From earlier studies it is known that at the core surface ripples are present that have the shape of "bamboo" waves or "snake" waves.

Theoretical and experimental investigation of acoustic streaming in a porous material.

An experimental and theoretical investigation of the influence of high-frequency acoustic waves on the flow of a liquid through a porous material has been made. Particular attention was paid to the phenomenon of acoustic streaming of the liquid in the porous material due to the damping of the acoustic waves. The experiments were performed on Berea sandstone cores.

An investigation of the influence of acoustic waves on the liquid flow through a porous material.

An experimental and theoretical investigation has been made of the influence of high-frequency acoustic waves on the flow of a liquid through a porous material. The experiments have been performed on Berea sandstone cores. Two acoustic horns were used with frequencies of 20 and 40 kHz, and with maximum power output of 2 and 0.