Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session PF: Microfluidics: Slip and Experimental Methods |
Hide Abstracts |
Chair: Minami Yoda, Georgia Institute of Technology Room: 101F |
Tuesday, November 24, 2009 11:40AM - 11:53AM |
PF.00001: The effect of tracer properties on interfacial particle-image velocimetry results in microflows Yutaka Kazoe, Minami Yoda Interfacial effects are important in many cases for microscale transport. One of the few experimental techniques that can resolve interfacial transport at these spatial scales is multilayer nano-particle-image velocimetry (MnPIV), which exploits the exponentially decaying intensity of evanescent-wave illumination to obtain velocities at different distances from the fluid-solid interface within 400 nm of the wall. Although MnPIV results have been validated in steady and creeping Poiseuille flow, the results of this technique, like all tracer-based velocimetry techniques are \underline {tracer }velocities, which are then assumed to be identical to the fluid velocities. This talk describes MnPIV results using tracers with diameters ranging from 40 nm to 100 nm for otherwise identical flows; changing tracer size should impact both electrostatic interactions and Brownian effects. Results are presented on how tracer size affects near-wall particle and velocity distributions in Poiseuille flow and electroosmotic ($i.e$., electrokinetically driven) flow, with the additional complication of particle electrophoresis, in channels with a minimum cross-sectional dimension of about 40 $\mu $m. [Preview Abstract] |
Tuesday, November 24, 2009 11:53AM - 12:06PM |
PF.00002: Depth of correlation reduction due to out-of-plane shear in microscopic PIV Michael Olsen The effects of out-of-plane shear on the depth of correlation in microscopic particle image velocimetry (microPIV) were analyzed by deriving an analytical model of microPIV interrogation for flowfields containing velocity gradients in the out-of-plane direction. The model is derived using a Taylor series approximation, and is therefore most accurate in the limit of small shear, but it does provide valuable insights. The model shows that out-of-plane velocity gradients reduce the depth of correlation compared to flowfields without gradients, but this decrease in depth of correlation is smaller than the increase in depth of correlation for a flowfield containing only in-plane velocity gradients. By combining the analysis for flows with in- plane gradients and with the analysis for flows with out-of-plane gradients, an equation for depth of correlation for a flowfield containing both in-plane and out-of-plane velocity gradients was derived. This equation suggests that unless the out-of-plane gradients are significantly larger than than the in-plane gradients, the effect on the depth of correlation due to the out-of-plane gradients is negligible, and the depth of correlation can be very closely approximated by calculating the depth of correlation using only the in-plane velocity gradients. [Preview Abstract] |
Tuesday, November 24, 2009 12:06PM - 12:19PM |
PF.00003: Extending micro-PIV to unsteady flows and real time 3D particle tracking using spinning disk confocal microscopy Steven Klein, Jonathan Posner A high speed micro particle imaging velocimetry system based on a spinning disk confocal microscope is presented. The confocal system uses a spinning disk with a series of pinholes arranged in an Archimedes spiral to optically section the sample, rejecting light originating from out of focus particles. Unsteady flows require two frame cross correlations and can be better resolved using the increased correlation signal to noise ratio provided by the confocal system, resulting in less erroneous vectors for the same validation criteria and illumination intensity. By utilizing a high speed CMOS camera we can obtain vector fields at up to 2500 Hz, which is ultimately limited by the speed of rotating pinhole disk. Volumetric scans of fluorescently labeled microspheres are acquired by rapid translation of the high numerical aperture objective using a piezo stage. High speed optical sectioning and volumetric scanning of microscopic volumes can be used for real time visualization and velocimetry of three dimensional flows and cellular processes. [Preview Abstract] |
Tuesday, November 24, 2009 12:19PM - 12:32PM |
PF.00004: Studies on Rheology of E-printing Inks by $\mu$-PIV in Microchannels Young-Sik Jang, Simon Song Using printing technologies for electronic circuits, such as antennas for radio frequency identification (RFID) chips, has been paid attention to recently in order to reduce production costs. In general, E-printing inks used for printed electronics have non-Newtonian properties because they contain metallic particles. Thus, it is important to investigate rheological behaviors of E-printing inks and suggest proper rheological models for developing printing devices for printed electronics. Also, the rheological models are necessary to accurately predict ink behaviors using CFD. However, classic methods to study rheological models are somewhat irrelevant since they require the mass consumption of expensive E-printing inks. Thus, to study rheological models suitable for commercial E-printing inks, we use microfluidic chips that only requires nascent E-printing inks. We measured flow velocities using $\mu $PIV and pressure drops along the microchannel to determine a relationship between stress and strain rate of ink flows. We found that the E-printing inks exhibit shear-thinning behaviors. In the presentation, we will propose rheology models suitable for the E-printing inks. [Preview Abstract] |
Tuesday, November 24, 2009 12:32PM - 12:45PM |
PF.00005: Imaging the liquid film layer of slug flow within a microreactor Shahram Pouya, Manoochehr Koochesfahani, Andrew Greytak, Daniel Nocera, Moungi Bawendi, Vicki Dydek, Klavs Jensen Segmented gas-liquid microreactors have gained attraction for high throughput material synthesis and sample processing in chemistry and biotechnology. The performance of the segmented gas-liquid microfluidic reactor derives from the uniformity of the gas-liquid segment lengths and the mixing that occurs within the liquid segment confined between gas slugs. The mixing process is a consequence of the recirculating flow that is set up within the liquid slugs. An important aspect of this flow geometry is that the liquid segments are not completely isolated but interconnected through a thin liquid film. Therefore, the behavior of the film layer and the flow field within the slugs are of great importance in hydrodynamics of the microreactor flow and improving the efficiency of such reactors. We present preliminary results of imaging, with quantum dots, the thin film layer surrounding the gas bubbles. The results are presented for stable slug flow of Ethanol/Nitrogen within a PDMS microreactor with channel size of 300$\times $250 micron. [Preview Abstract] |
Tuesday, November 24, 2009 12:45PM - 12:58PM |
PF.00006: A simple microfluidc method for rapid generation of long-range material gradients in microchannels Matthew Hancock, Yanan Du, Jinkang He, Jose Uribe-Villa, Ali Khademhosseini The ability to recreate the heterogeneity of cellular environments is a major challenge for investigating cell- material interaction and for developing biomimetic materials for tissue engineering. Here we present a simple fluidic method for rapidly generating 2-3 cm gradients of biomolecules, polymers, microbeads, and cells. A polymer hydrogel gradient and a composite material with a cross-gradient of hyaluronic acid (HA) and gelatin in different ratios were generated with continuous variations in material properties. The approach relies on hydrodynamic stretching of the concentration profile and, for molecular species, enhanced lateral molecular diffusion. Faster gradient growth occurs for large Peclet numbers, outside the Taylor-Aris parameter range. Computational simulations and user-friendly power law formulas provide estimates of gradient growth for a wide range of Peclet numbers and channel cross-sections. Our microfluidic platform is limited to a rectangular PDMS microchannel and a syringe pump and should be accessible to a broad range of experimenters in the materials science and biomedical fields. [Preview Abstract] |
Tuesday, November 24, 2009 12:58PM - 1:11PM |
PF.00007: Modeling the combined effect of surface roughness and shear rate on slip flow of simple fluids Anoosheh Niavarani, Nikolai Priezjev Molecular dynamics (MD) and continuum simulations are carried out to investigate the influence of shear rate and surface roughness on slip flow of a Newtonian fluid. The nonlinear shear-rate dependence of the intrinsic slip length in the flow over an atomically flat surface is computed by MD simulations. We describe laminar flow away from a curved boundary by means of the effective slip length defined with respect to the mean height of the surface roughness. Both the magnitude of the effective slip length and the slope of its rate-dependence are significantly reduced in the presence of periodic surface roughness. We then numerically solve the Navier-Stokes equation for the flow over the rough surface using the rate-dependent intrinsic slip length as a local boundary condition. Continuum simulations reproduce the behavior of the effective slip length obtained from MD simulations at low shear rates. The slight discrepancy between MD and continuum results at high shear rates is explained by examination of the local velocity profiles and pressure distribution along the wavy surface. We found that in the region where the curved boundary faces the mainstream flow, the local slip is suppressed due to the increase in pressure. [Preview Abstract] |
Tuesday, November 24, 2009 1:11PM - 1:24PM |
PF.00008: Shear flow over arbitrary periodic surfaces Ken Kamrin, Howard Stone, Martin Bazant In a variety of applications, notably microfluidics, slip-based boundary conditions have been sought to characterize fluid flow over patterned surfaces. This work focuses on shear flows of Stokes fluid over surfaces with small height fluctuations and/or fluctuating Navier slip properties. Our goal is to derive a general formula to determine the ``effective slip'' in terms of surface properties and the applied shear stress. We show that the slip and the applied stress are always related linearly through a slip matrix, representing a tensorial mobility. The method of domain perturbation is then used to deduce an approximate formula for the slip matrix. We use the formula to determine optimal surface shapes and the effect of random fluctuations on fluid slip. [Preview Abstract] |
Tuesday, November 24, 2009 1:24PM - 1:37PM |
PF.00009: Navier-slip and other viscous flow boundary conditions using penalty methods Yvonne Stokes, Graham Carey With the advent of microscale and nanoscale devices, the Navier-slip boundary condition as a macroscale model of fluid behaviour at a solid wall has seen renewed interest. The penalty concept and variational formulation are extended here to treat partial slip, free surface, contact and related boundary conditions for boundaries of general shape in viscous flow simulation. We analyse the penalty partial-slip formulation and relate it to the classical Navier-slip condition. A variant of the same penalty scheme also allows partial penetration through a boundary and, hence, the implementation of porous wall boundaries with leakage or ``blowing and suction.'' Finally the scheme can be employed in a novel way to handle moving contact lines. [Preview Abstract] |
Tuesday, November 24, 2009 1:37PM - 1:50PM |
PF.00010: A hybrid simulation of the atomistic-continuum methods for fluid flows on superhydrophobic surfaces Guowei He, Qiang Li It has been found from recent experiments that the fluid flows on superhydrophobic surfaces could have the slip length as large as the order of a micro-meter. The superhydrophobic surfaces can be achieved by patterning roughness on hydrophobic surfaces. In the present paper, an atomistic-continuum hybrid approach is developed to simulate the Couette flows over superhydrophobic surfaces, in which a molecular dynamics simulation is used to a small region near the superhydrophobic surface where the continuum assumption is not valid and the Navier-Stokes equations are used in a large region for bulk flows where the continuum assumption does hold. These two descriptions are coupled using the dynamic coupling model in the overlap region to ensure the momentum continuity. The hybrid simulation predicts a superhydrophobic state with the large slip lengths which cannot be obtained by molecular dynamics simulation alone. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700