Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session EA: Micro Fluids: General I |
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Chair: Steve Wereley, Purdue University Room: Salt Palace Convention Center 150 A-C |
Sunday, November 18, 2007 4:10PM - 4:23PM |
EA.00001: Electrospinning of aequeous latex dispersions of water-insoluble polymers Florian Grossmann, Bruno Eckhardt, Aleksandar Stoiljkovic, Andreas Greiner Electrospinning of aequous dispersions of polysterene latex spheres together with some polyvenylalcohol results in fibres with chains of polysterene spheres as a backbone. The dynamics of the aggregation is modelled within an effective field ansatz for the flow and a two-particle potential for the latex sphere interactions. The simulations give backbones with different degrees of order and strength, in agreement with observations. [Preview Abstract] |
Sunday, November 18, 2007 4:23PM - 4:36PM |
EA.00002: Prediction of scaling law for particle diffusion in polymer solutions Tai-Hsi Fan, Remco Tuinier Particle diffusion plays an important role affecting mass transport and reaction kinetics in many biological systems. In a crowded physiological microenvironment, diffusion transport of particles or macromolecules is hindered by the background biopolymers such as proteins and polysaccharides. In a simplified model system, such hindering or retardation effect is often described by a stretched exponential function, $R=$exp(\textit{Ka}$^{\mu }c^{\nu })$, where $R$ is the empirical retardation factor to be measured from the particle's apparent diffusivity in polymer solutions, $a$ is the particle size, $c$ is the bulk polymer concentration, and the coefficient $K $and exponential scaling exponents \textit{$\mu $} and \textit{$\nu $ }are empirical parameters. A few hypotheses were proposed to rationalize the scaling exponents, but there is yet no satisfactory theoretical proof that $R$ can be expressed in such a general fashion. We propose analytical and numerical models to compute the retardation effect based on continuum fluid flow analysis and polymer depletion theory. The three important empirical parameters are predicted for both dilute and semi-dilute polymer solutions. The found scaling law resembles the nominal values of the exponential exponents from collected experimental data, providing a promising explanation for the polymer-mediated retardation effect. [Preview Abstract] |
Sunday, November 18, 2007 4:36PM - 4:49PM |
EA.00003: Acoustic streaming in resonant viscous microfluidic systems Peder Skafte-Pedersen, Henrik Bruus Within the field of lab-on-a-chip systems large efforts are devoted to the development of onchip tools for particle handling and mixing in viscosity-dominated microflows. One technology involves ultrasound with frequencies in the MHz range, which leads to wavelengths of the order of $10^{-4}-10^{-3}$~m suitable for mm-sized microchambers. Due to the nonlinearity of the governing acoustofluidic equations, second-order effects will induce steady forces to fluids and suspended particles through the effects known as acoustic streaming and acoustic radiation pressure. We present the basic perturbation approach for treating these effects in systems at resonance, where the amplitudes are maximized. The first-order eigenmodes are used as source terms for the time-averaged viscous second-order equations. The theory is applied to explain experimental results on aqueous microbead solutions in silicon-glass microchips [1].\\ \\ {}[1] S. M. Hags\"{a}ter, T. Glasdam Jensen, H. Bruus and J. P. Kutter.\\ \textit{Acoustic resonances in microfluidic chips: full-image micro-PIV experiments and numerical simulations.} Lab Chip, 2007, DOI: 10.1039/b704864e. [Preview Abstract] |
Sunday, November 18, 2007 4:49PM - 5:02PM |
EA.00004: Particle transport on periodic potential landscapes Aloke Kumar, Nung Yip, Steve Wereley Particles in a periodic potential landscape and undergoing transport under the influence of an external force experience an overall deviation from the prescribed direction of the force. Such a deviation can vary as a function of particle size, resulting in effective sorting technique. We extend an earlier proposed physical model for such situation to show how time dependent lattice structures can act as an effective sorting mechanism. Transport behaviors in different, but easily realizable lattice structures, are studied. These behaviors can be sensitive to different parameters. Two separate regimes - one with particle inertia and one without are studied and effective parameters for both cases are established. Thermal fluctuations are also incorporated in the model due to the increased interests in such sorting procedures for colloidal microscale fluid flow. Numerical findings are compared to some recently reported experimental results, as well as our own data which are obtained using holographic optical traps. These traps are easily reconfigurable, which makes them ideal candidates for practical simulations of such physical phenomena. [Preview Abstract] |
Sunday, November 18, 2007 5:02PM - 5:15PM |
EA.00005: ABSTRACT WITHDRAWN |
Sunday, November 18, 2007 5:15PM - 5:28PM |
EA.00006: Nonlinear electro-phoresis of conducting particles Ehud Yariv When an initially-charged conducting spherical particle is placed under an externally-imposed uniform electric field, its surface-charge distribution is modified from its original uniform state, and the Debye layer adjacent to its boundary is accordingly polarized. The ensuing asymmetric zeta-potential profile leads to electrophoretic particle motion. In the thin-Debye-layer limit, this problem is characterized by three voltage scales, associated with the respective effects of initial charge, applied field, and ionic thermal motion. Charge conservation provides an implicit relation between the electrophoretic mobility and these quantities. Due to the nonlinear Debye-layer capacitance, the electrophoretic mobility differs from that of a dielectric particle possessing the same net electric charge. The mobility dependence upon the applied-field magnitude and the initial charge is investigated using both direct and asymptotic methods. The inherent nonlinearity results in some counter-intuitive effects, the most notable of these is the mobility subsidence for strongly-applied fields. [Preview Abstract] |
Sunday, November 18, 2007 5:28PM - 5:41PM |
EA.00007: Kinetic theory for cross-stream migration in dilute solutions of rigid polymers and Brownian fibers undergoing rectilinear flow near a wall Joontaek Park, Jonathan Bricker, Jason Butler We present a kinetic theory for the migration of a dilute solution of rigid polymers and Brownian fibers undergoing rectilinear flows and include hydrodynamic interactions with the bounding walls. The results clarify the origin and direction of the migration observed in experiments and recent simulations. We show results for a rigid polymer undergoing simple shear flow near a single wall and pressure-driven flow between two bounding walls. In simple shear flow, rigid polymers migrate away from the wall due to hydrodynamic interactions with the wall, creating a depletion layer in the vicinity of the wall which thickens as the flow strength increases relative to the Brownian force. In pressure-driven flow, an off-center maximum in the center-of-mass distribution occurs due to a competition between hydrodynamic interactions with the wall and the anisotropic diffusivity induced by the inhomogeneous flow field. [Preview Abstract] |
Sunday, November 18, 2007 5:41PM - 5:54PM |
EA.00008: Micro-Scale Couette-Poiseuille Flow in Curved Microchannels Ala'aldeen Al-Halhouli, Mohammad Kilani, Ahmad Al-Salaymeh, Stephanus Buettgenbach This work presents an extended flow model estimates for the combined effect of geometrical design parameters: channel aspect ratio, mean radius to width ratio, and polar slope ratio on the Couette-Poiseuille flow in curved microchannels. For this purpose analytical and numerical investigations were performed at different boundary conditions. The flow in spiral channel, single and double disks micropumps are Couette-Poiseuille like flow and depend on dragging the fluid between the ends of the curved protrusion by spinning a flat disk in close proximity over the curved microchannel. The flow is generated due to a net tangential viscous stress on the boundaries which produces a positive pressure gradient in the direction of flow. The combined effect of the geometrical design parameters was expressed through defining drag and pressure shape factors. The analytical estimations were verified numerically and compared with the experimental. Results show that the flow rate varies linearly with both the pressure difference and boundary velocity. The obtained extended approximate model depicts complete representation for the effect of channel width, height, polar slope, spiral length, and mean radius on the flow through curved microchannels. [Preview Abstract] |
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