Fluids in Small Confined Spaces Stirred with Self-Assembled Chains of Iron Beads
- PDF / 54,447 Bytes
- 1 Pages / 576 x 783 pts Page_size
- 102 Downloads / 176 Views
Fluids in Small Confined Spaces Stirred with Self-Assembled Chains of Iron Beads Mixing in microfluidic channels is difficult because confined spaces inhibit viscosity-induced turbulence. Diffusive mixing can occur in these situations, but some devices utilizing submillimeter channels require faster mixing than this achieves. Pursuing stirring methods at the micrometer-scale is therefore a priority for lab-on-a-chip applications, and the most useful methods utilize the strong, long-range interaction between a magnet and a magnetic field. As reported in the July issue of Physical Review E (DOI: 10.1103/PhysRevE.80.016312; #016312), J.E. Martin, L. Shea-Rohwer, and K.J. Solis of Sandia National Laboratories have introduced a method of mixing fluids with self-assembled chains of 4–7 μm carbonyl iron beads driven by a magnetic vortex field. A vortex field is a combination of three fields, two perpendicular sinusoidal fields oscillating 90° out of phase (a rotating field) and a third normal to their plane. By measuring the angular deflection due to the vortex magnetic field of 150 mg of Fe particles in 2 ml solution, the re searchers measured the torque
Piezomagnetoelastic Device Harvests Vibrational Energy In the current era of energy awareness, the ability to recover energy wasted as heat or vibration is an important component of conservation. Commonly called “energy harvesting,” it requires a way to gather and store minute amounts of energy, a complex problem that is leading researchers to novel materials solutions. As reported recently in Applied Physics Letters (DOI: 10.1063/1.3159815; #254102), researchers A. Erturk, J. Hoffmann, and D.J. Inman, from Virginia Polytechnic Institute and State University, have devised a system for harvesting vibrational energy based on a magnetoelastic structure originally studied for the type of behavior known in chaos
Soot Aggregates from Pre-Mixed Flame Observed to Have Low Fractal Dimension Fractal-like soot particles are among the combustion-generated carbonaceous aerosols that influence Earth’s radiation balance, climate, atmospheric chemistry, and therefore the welfare of all its living
imparted to several fluids with viscosities varying by an order of magnitude. They found that the mixing is optimized when
the ac field and dc field magnitudes are equal. A sample of the magnetic powder was suspended in resin to test if the deflection measured was due to the magnetic torque of the beads or the torque imparted to the fluid. The resin did not move, from which the researchers inferred that the frequency-dependent susceptibility of the iron plays a negligible role. The researchers found that the iron beads did not rotate independently; rather they stirred the liquids by forming magnetically linked chains (see Figure 1). Because chains fragment as they whirl around faster, the chain imparts a constant torque to the fluid as the frequency of the vortex field increases. This is not what happens with a magnetic stir-bar. The research team found that this action also keeps the mixin
Data Loading...
