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 GA: Micro Fluids: General III |
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Chair: Jonathan Posner, Arizona State University Room: Salt Palace Convention Center 150 A-C |
Monday, November 19, 2007 10:30AM - 10:43AM |
GA.00001: Directional dependence of depth of correlation due to fluid shear in microscopic particle image velocimetry Michael Olsen An analytical model for the microscopic particle image velocimetry (microPIV) correlation signal peak in a purely shearing flow was derived. This model was then used to derive equations for the measured velocity weighting functions for the two velocity components, and the weighting functions were in turn used to define the depths of correlation associated with the two measured velocity components. The depth of correlation for the velocity component perpendicular to the shear was found to be unaffected by the shear rate. However, the depth of correlation for the velocity component in the direction of the shear was found to be highly dependent on the shear rate, with the depth of correlation increasing as shear rate increased. Thus, in a flow with shear, there is not a single value for the depth of correlation within an interrogation region. Instead, the depth of correlation exhibits directional dependence, with a different depth of correlation for each of the two measured velocity components. The increase in the depth of correlation due to shear rate is greater for large numerical aperture objectives than for small numerical aperture objectives. This increase in the depth of correlation in a shearing flow can be quite large, with increases in the depth of correlation exceeding 100\% very possible for high numerical aperture objectives. [Preview Abstract] |
Monday, November 19, 2007 10:43AM - 10:56AM |
GA.00002: Three component velocity extraction method using TR-PIV in a microtube Nejdet Erkan, Koji Okamoto, Satoshi Someya Measurement of three-component (3C) velocity field in the microfluidic devices with the conventional techniques and conventional micro-PIV (Particle Image Velocimetry) is still difficult due to the limited optical access to the microscale flow fields. Since Santiago \textit{et al} (1998), micro-PIV flow velocity measurements have remained mainly limited to the 2C velocity vector field realizations. In this study, third component of the velocity i.e. out-of-plane velocity extraction from two-dimensional time resolved (TR) micro-PIV images is proposed. The method is based on PIV and performs cross-correlation (CC) peak height tracking inside the small ensembles of the TR-PIV flow images. This concept was verified basically by the simulation employing synthetic micro TR-PIV images. It was also demonstrated by an experiment erformed on a microscale fluid flow inside a 100$\mu $m diameter inclined micro tube. Despite the inevitable background noise which effects the measurement negatively, extracted steady-state depthwise velocity profile was in agreement with the analytical result. [Preview Abstract] |
Monday, November 19, 2007 10:56AM - 11:09AM |
GA.00003: Measurement of particle trajectories, dynamics, surface adhesion and detachment in near-wall shear flows using 3D velocimetry Jeffrey Guasto, Brian Schmidt, Michael Lawrence, Kenneth Breuer Three-dimensional total internal reflection velocimetry (3D-TIRV) is used to measure the trajectories of fluorescent tracer particles within 200 nm of a wall. Diffusion and shear-induced motion can result in mean velocity measurement errors, and by taking measurements using different particle sizes and sampling times, we quantify these effects and compare with theory. We also use 3D-TIRV to observe and characterize the adhesion, surface rolling and release dynamics of particles that can adhere to the surface through the action of biological binding proteins. Particles coated with P-Selectin are allowed to adhere to and detach from a PSGL-1-coated microchannel surface, modeling the interaction between leukocytes (white blood cells) and blood vessels, respectively. Binding affinities, bond strengths and hydrodynamic interactions are inferred from the trajectory data. [Preview Abstract] |
Monday, November 19, 2007 11:09AM - 11:22AM |
GA.00004: A Microscopic Particle Image Velocimetry Study of the Structure of Transitional Capillary Flow V.K. Natrajan, K.T. Christensen Instantaneous velocity realizations in the streamwise--wall-normal plane of a 536-micron glass capillary are acquired by micro-PIV for Reynolds numbers in the transitional and fully-turbulent regime (Re=2300, 2700, 3100 and 4500, respectively). Examination of the ensembles at the transitional Re reveals that they are composed of a subset of velocity fields illustrating laminar behavior and a subset that capture significant departure from laminar behavior. The instantaneous non-laminar velocity fields at the transitional Re contain multiple spanwise vortices that appear to streamwise-align to form larger-scale interfaces inclined slightly away from the wall. These characteristics are consistent with hairpin vortex packets that are often observed in transitional and fully-turbulent wall-bounded flow at the macroscale. Similar spatial signatures are also noted in various estimates of conditionally-averaged velocity fields. Finally, eigenvalue spectra are computed via proper orthogonal decomposition (POD) for the non-laminar subsets at the transitional Re and reveal increasing energy content within the higher-order modes as the flow matures to a fully-turbulent state. Such behavior indicates that this maturation process is accompanied by a gradual evolution of smaller wall-normal length scales that become more energetic with increasing Re. [Preview Abstract] |
Monday, November 19, 2007 11:22AM - 11:35AM |
GA.00005: Spinning Disk Confocal microPIV of Unstable Non-dilute Electrokinetic Flows Steven Klein, Jonathan Posner Flow velocity is measured in microscale flows using microPIV and a Nipkow spinning disk based confocal microscope. The confocal system provides for optical sectioning thinner than 500 nm which allows for rejection of light originating from out of focus particles. Out of focus light in standard microPIV typically results in depth averaging, poor SNR, and the inability to measure unsteady flows. Spinning disk confocal imaging provides depth resolved imaging, high SNR images with increased particle volume fractions, and imaging rates of 200 frames per second (limited by the CCD). In this work, two velocity components are measured in a volume in a steady pressure driven flow. The system is also applied to measuring two components of velocity of unstable electrokinetic flows in non-dilute colloidal suspensions. [Preview Abstract] |
Monday, November 19, 2007 11:35AM - 11:48AM |
GA.00006: Microfluidic flow-dependent optical particle trapping and circulation. David Sinton, Thomas Blakely, Reuven Gordon Through the planar integration of microfluidics and fiber optics, flow-dependent optical trapping and stable circulation are achieved. Two configurations are demonstrated: Single tapered fiber traps aligned with the up-stream flow direction; and dual fiber cross-flow optical traps with alignment bias relative to the flow direction. In both configurations, particle trapping results from a combination of flow-induced drag force and optical scattering forces. In the tapered fiber traps, the stable particle trapping is achieved through a balance of forward scattering and fluid drag force, with particle position indicating the relative strength each. In the dual fiber traps, two fibers are oriented in the cross-stream direction. Employing a bias in the optical fiber in-plane alignment angle results in a flow dependence for stability and circulation. The result is a microfluidic flow-dependent circulating optical trap which may be employed to indicate flow direction, magnitude, or employed to mix co-laminar streams. A strong dependence on particle size also indicates potential for stream-wise particle sorting by size. Lastly, two extensions of this work are discussed: Microfluidic and optical interactions in multiphase (oil-water-particle) systems; and flow dependencies of optically-trapped linear arrays of particles. [Preview Abstract] |
Monday, November 19, 2007 11:48AM - 12:01PM |
GA.00007: Active, Universal Particle Micromanipulators: CPUs for Microfluidics Igor Mezic, Frederic Bottausci Current designs for Lab-on-a-Chip applications consist of a variety of separate microfluidic chambers and channels for functions such as concentration, separation, reaction and mixing of bioparticles in liquids. Here we advance an alternative concept, named \textit{$\mu $f}CPU, the Microfluidic Central Processing Unit, where the key microfluidic operations are performed within a single enclosure, using software-based inputs rather than physical hardware changes, thus emulating the role of the Central Processing Unit in computers and cells in living organisms. We present an experimental embodiment of such a device and describe a variety of microfluidic manipulation tasks achieved in it by the use of a suite of electromotive and fluidic forces in a time-dependent way to produce on-demand functionality. We also discuss a new microfluidic devices architecture that utilizes \textit{$\mu $f}CPU as the basic processing unit and uses centralized pumping instead of integrated microfluidic pumps. [Preview Abstract] |
Monday, November 19, 2007 12:01PM - 12:14PM |
GA.00008: Optically-Controlled Thermocapillary Actuation of Microdroplets at a Fluid Interface Daniel Borrero, Edwin F. Greco, John E. Widloski, Dmitri L. Vainchtein, Roman O. Grigoriev, Michael F. Schatz Laser actuation can be used to perform microfluidic operations on droplets floating at a liquid-air interface by exploiting the thermocapillary effect. A model has been developed to describe the velocity field in the interior of such droplets. Measurements of the temperature field in the substrate, which are crucial for accurate numerical simulations of the system, are presented. Fluorescent tracers are used to visualize the three-dimensional mixing properties of the flow in the interior of the droplet using dual microscopes. [Preview Abstract] |
Monday, November 19, 2007 12:14PM - 12:27PM |
GA.00009: Laminar and Turbulent Flow of a Liquid through Microchannels with Walls Exhibiting Wetting and Non-Wetting Cavity Regions Brady Woolford, Daniel Maynes, Brent Webb, Brian Jensen Recent developments in micro-scale systems have enabled significant reduction in the frictional drag for liquid flow through microchannels. To accomplish this the channel walls are created by patterning microribs and cavities onto a substrate and then treated with a hydrophobic coating. There is an apparent risk when using such surfaces, however, that the Laplace pressure may be exceeded and that the liquid will wet the cavities. Results that compare the flow dynamics through channels that exhibit wetted and non-wetted cavities, oriented both parallel and transverse to the direction of flow will be presented and discussed. The results show the reduction in the total frictional resistance is much greater in channels when the liquid phase does not enter the cavities, both when the ribs/cavities are oriented parallel to the flow direction and when they are oriented transverse to the flow direction. Measurements of the frictional resistance for transitional and turbulent flows in such microchannels where the liquid has wet the cavity walls will also be presented and discussed. Results are presented for Reynolds numbers ranging from 2 to 10,000, microchannel hydraulic diameters ranging from 180 -- 500 \textit{$\mu $}m, microrib widths ranging from 3 -- 20 \textit{$\mu $}m, and microcavity widths ranging from 20 -- 60 \textit{$\mu $}m. [Preview Abstract] |
Monday, November 19, 2007 12:27PM - 12:40PM |
GA.00010: Flow of polymer solutions in planar 90 degree micro-bends Dorian Liepmann, Shelly Gulati, Cari Dutcher, Susan Muller The characterization of flows containing macromolecules is critical for the optimal design of microfluidic systems for biochemical analyses. The effects on transport in microscale flows are significant because the flow behavior may be influenced by molecular interactions, both viscous and elastic forces dominate inertial forces at this length scale, and the macromolecular length scale L approaches the device length scale D. Our previous studies explored flows of semi-dilute DNA solutions in planar 90 degree micro-bends (L/D $\sim $ 0.09), a canonical microfluidic structure; macromolecular flows in this geometry on a macro or microscale had been essentially unexplored. A recirculation region present in the interior corner of the bend is enhanced with increasing Re (7 x 10$^{-7} <$ Re $<$ 8 x 10$^{-4})$ and Wi (1 $<$ Wi $<$ 190). Flows of poly(ethylene) oxide (PEO) solutions are explored across a similar parameter range to determine the influence of polymer extensibility and flexibility on the instability. Comparison of flows of DNA and PEO solutions offers insight into physical mechanism for the formation of elastic instabilities in micro-geometries. [Preview Abstract] |
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