Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session L11: Microscale Flows: Oscillations and Magnetic Manipulation |
Hide Abstracts |
Chair: Brian Storey, Olin College of Engineering Room: 3007 |
Monday, November 24, 2014 3:35PM - 3:48PM |
L11.00001: Theory and numerical analysis of thermoviscous effects in ultrasound-induced acoustic streaming in microchannels Peter Barkholt Muller, Henrik Bruus We present a numerical study of the thermoviscous effects on the acoustic streaming flow generated by an ultrasound standing wave resonance in a long straight microfluidic channel. These effects enter through the temperature and density dependence of the fluid viscosity. The resulting magnitude of the streaming flow is calculated and characterized numerically, and remarkably, we find that even for thin acoustic boundary layers, the channel height affects the magnitude of the streaming flow. For the special case of a sufficiently large channel height we have successfully validated our numerics with analytical results from 2011 by Rednikov and Sadhal for a planar wall. Furthermore, the time-averaged energy transport in the system is analyzed, and the time-averaged second-order temperature perturbation of the fluid is calculated. [Preview Abstract] |
Monday, November 24, 2014 3:48PM - 4:01PM |
L11.00002: Oscillations of free cylinders at low Reynolds numbers inside a Hele-Shaw cell J.-P. Hulin, V. D'Angelo, L. Gianorio, M. Cachile, H. Auradou, B. Semin We study two instabilities of a horizontal free cylinder in a vertical viscous Hele-Shaw flow: they are shown experimentally to depend critically on the transverse and lateral confinement of the flow characterized respectively by the ratios $D/H$ (resp. $L/W$) of the diameter (resp. the length) of the cylinder to the gap (resp. the width) of the cell. The onset of the instabilities depends essentially on $D/H$. For $0.4 \le D/H \le 0.6$, we observe transverse horizontal oscillations of the cylinder perpendicular to the walls: their frequency is constant with $D/H$ and $L/W$ at a given vertical cylinder velocity $V_c$. This instability is locally $2D$ along the length of the cylinder and controlled by the local relative velocity $V_r^{loc}$ of the cylinder and the fluid: it occurs down to Reynolds numbers $Re^{loc} = V_r^{loc}H/\nu \simeq 15 $, i.e. below the vortex shedding threshold ($150-250$) for fixed cylinders between parallel planes. These results are compared to $2D$ numerical simulations. For $D/H \ge 0.55$, we observe a fluttering motion with periodic oscillations of the tilt angle of the cylinder from the horizontal and of its horizontal position: their frequency decreases as $L/W$ increases and is independent of $D/H$ and $V_c$. [Preview Abstract] |
Monday, November 24, 2014 4:01PM - 4:14PM |
L11.00003: Taylor Dispersion in Oscillatory Flow in Rectangular Channels Jinkee Lee, Anubhav Tripathi, Anuj Chauhan This paper focuses on exploring the effect of the side walls on dispersion in oscillatory Poiseuille flows in rectangular channels. The method of multiple time scales with regular expansions is utilized to obtain analytical expressions for the effective dispersivity $D_{3D}^{\ast}$. The dispersion coefficient is of the form$\frac{D_{3D}^{\ast}}{Pe^{2}}=f(\Omega \equiv \frac{\omega h^{2}}{D},Sc\equiv \frac{D}{\nu},\chi \equiv \frac{w}{h})$ where $Pe\equiv \frac{< u > h}{D}$, \textless u\textgreater is the root mean square of the cross-section averaged velocity, $\omega$ is the angular velocity, 2w and 2h are the width and the height of the cross-section, $D$ is the solute diffusivity, $\nu$ is the fluid kinematic viscosity. The analytical results are compared with full numerical simulations and asymptotic expressions. Also effect of various parameters on dispersion coefficient is explored. For small oscillation frequency $\Omega$, the dispersion coefficient approaches the time averaged dispersion of the Poiseuille flow and for large $\Omega $, $D_{3D}^{\ast } $scales as \textit{Pe}$^{2}$/$\Omega^{2}$ where \textit{Pe}$=$\textless $u$\textgreater $h/D$. Due to its relative simplicity, the 2D model is frequently utilized for calculating dispersion in channels. However at small dimensionless frequencies, the 2D model can significantly underestimate the dispersion, particularly for channels with large $\chi$. At large $\Omega$, the dispersion coefficient predicted from the 2D model becomes reasonably accurate, particularly for channels with large $\chi$. For a square channel, the 2D prediction is reasonably accurate for all frequencies. The results of this study will enhance our understanding of transport in microscale systems that are subjected to oscillating flows, and potentially aid technological advances in diverse areas relevant to microfluidic devices. [Preview Abstract] |
Monday, November 24, 2014 4:14PM - 4:27PM |
L11.00004: Experimental and numerical analysis of the steady streaming around a cylinder pair E. Gal\'an-Vicente, W. Coenen The steady streaming motion that develops around a cylinder pair in small-amplitude oscillatory flow, is studied experimentally and numerically. The axes of the cylinders are perpendicular to the plane of motion, and the angle that the flow makes with the line connecting the cylinder centers, as well as the distance between them, is varied. We focus on the regime where the ratio $\epsilon$ of the amplitude of oscillation to a cylinder radius $a$ is small. A theoretical analysis shows that the action of the Reynolds stresses in thin Stokes shear-wave layers close to the cylinder surfaces induces a steady streaming motion that persists at the edge of these layers with velocities of $\mathcal{O}(\epsilon U)$, where $U$ is the velocity amplitude of the basic oscillatory flow. This streaming velocity at its turn drives an outer flow, governed by the steady Navier-Stokes equations with streaming Reynolds number $R_s = \epsilon U a/\nu$. We consider cases with $R_s \gg 1$. The steady equations are solved numerically, imposing the streaming velocity obtained from the asymptotic analysis as a slip boundary condition at the cylinder surfaces. The resuling flow patterns show good agreement with experimental flow visualizations in the form of phase-averages over various oscillation cycles. [Preview Abstract] |
Monday, November 24, 2014 4:27PM - 4:40PM |
L11.00005: The Temporal Resolution of Laser Induced Fluorescence Photobleaching Anemometer Wei Zhao, Fang Yang, Guiren Wang Recently, in microfluidics, electrokinetic flows are widely used on micromixer designing. However, there is unfortunately no valid velocimeter today that can measure the random velocity fluctuation at high temporal and spatial resolution simultaneously in the complicated flow circumstance. We recently introduced laser induced fluorescence photobleaching anemometer (LIFPA), which has been successfully used in the measurement of velocity field in AC electrically driven microflow. Here, we theoretically study the temporal resolution (TR) of and experimentally verify, LIFPA can have simultaneously ultrahigh temporal ($\sim $4 $\mu$s) and spatial ($\sim $203 nm) resolution and can measure velocity fluctuation up to at least 2 kHz, whose corresponding wave number is about 6 $\times$ 10$^{6}$ 1/m in an electrokinetically forced unsteady flow in microfluidics. The measurement of LIFPA is also compared with the widely used micro Particle Imaging Velocimetry ($\mu $PIV). We found, at the inlet, due to multiple uncertainties, the velocity fluctuations by $\mu $PIV exhibits apparently smaller values than that by LIFPA. But at downstreams, where velocity fluctuation is much lower than at the inlet and the uncertainties of complicated electric field on particles becomes smaller, LIFPA and $\mu $PIV indicate similar measurement. [Preview Abstract] |
Monday, November 24, 2014 4:40PM - 4:53PM |
L11.00006: Compact Two-Liquid Microfluidic Hyperelastic Capacitive Strain Sensors Shanliangzi Liu, Xiaoda Sun, Konrad Rykaczewski Applications of liquid metal microfluidic devices include flexible electronics, biomedical devices, and soft robotics. In addition to single channel resistive strain sensors, two channel capacitive sensors have also been developed. However, these capacitive strain sensors have low capacitance with a footprint of about a square centimeter, making strain-output correlation quite complex [1]. To address this issue, we developed a compact two liquid single straight channel capacitive strain sensor with a dielectric liquid sandwiched between two liquid metal electrodes. Formation of the capacitor with a liquid dielectric instead of PDMS enables capacitance increase through selection of high permittivity liquid. Using a custom experimental setup, we show that use of water and glycerol instead of silicone oil in-between the liquid metal electrodes can increase the device capacitance by fivefold. We discuss the effect of channel diameter, dielectric spacing, interfacial meniscus shape, and the liquid flow on device capacitance as well as response to strain. In addition, we discuss the effect of gallium oxide shell formation at the dielectric-liquid metal interface.\\[4pt] [1] Fassler A. and Majidi C. Smart Mater. Struct. 22 (2013). [Preview Abstract] |
Monday, November 24, 2014 4:53PM - 5:06PM |
L11.00007: Sound-induced Interfacial Dynamics in a Microfluidic Two-phase Flow Sze Yi Mak, Ho Cheung Shum Retrieving sound wave by a fluidic means is challenging due to the difficulty in visualizing the very minute sound-induced fluid motion. This work studies the interfacial response of multiphase systems towards fluctuation in the flow. We demonstrate a direct visualization of music in the form of ripples at a microfluidic aqueous-aqueous interface with an ultra-low interfacial tension. The interface shows a passive response to sound of different frequencies with sufficiently precise time resolution, enabling the recording of musical notes and even subsequent reconstruction with high fidelity. This suggests that sensing and transmitting vibrations as tiny as those induced by sound could be realized in low interfacial tension systems. The robust control of the interfacial dynamics could be adopted for droplet and complex-fiber generation. [Preview Abstract] |
Monday, November 24, 2014 5:06PM - 5:19PM |
L11.00008: Conformal coating of non-spherical magnetic particles using microfluidics Byeong-Ui Moon, Navid Hakimi, Dae Kun Hwang, Scott Tsai We present the conformal coating of non-spherical magnetic particles in a microfluidic channel. We first prepare three-dimensional (3D) bullet-shaped magnetic microparticles using stop-flow lithography. We then suspend the bullet-shaped microparticles in an aqueous solution, and flow the particle suspension with a co-flow of a non-aqueous mixture. A magnetic field gradient from a permanent magnet pulls the microparticles in the transverse direction to the fluid flow, until the particles reach the interface between the immiscible fluids. In a physical domain characterized by a low particle Reynolds number and a high magnetic Bond number, we observe that the microparticles cross the oil-water interface, and then become coated by a thin film of the aqueous fluid. When we increase the two-fluid interfacial tension by reducing the surfactant concentration, we observe that the particles become trapped at the interface. We use this observation to approximate the magnetic susceptibility of the manufactured non-spherical microparticles, which are not known a priori. Using fluorescence imaging, we confirm the uniformity of the thin film coating along the surface of the bullet-shaped particles. [Preview Abstract] |
Monday, November 24, 2014 5:19PM - 5:32PM |
L11.00009: Particle Transport and Size Sorting in Bubble Microstreaming Flow Raqeeb Thameem, Bhargav Rallabandi, Cheng Wang, Sascha Hilgenfeldt Ultrasonic driving of sessile semicylindrical bubbles results in powerful steady streaming flows that are robust over a wide range of driving frequencies. In a microchannel, this flow field pattern can be fine-tuned to achieve size-sensitive sorting and trapping of particles at scales much smaller than the bubble itself; the sorting mechanism has been successfully described based on simple geometrical considerations. We investigate the sorting process in more detail, both experimentally (using new parameter variations that allow greater control over the sorting) and theoretically (incorporating the device geometry as well as the superimposed channel flow into an asymptotic theory). This results in optimized criteria for size sorting and a theoretical description that closely matches the particle behavior close to the bubble, the crucial region for size sorting. [Preview Abstract] |
Monday, November 24, 2014 5:32PM - 5:45PM |
L11.00010: Interfacial deformation and jetting of a magnetic fluid Shahriar Afkhami, Linda Cummings An attractive experimental technique, for forming and collecting aggregates of magnetic material at a liquid-air interface by an applied magnetic field, was recently addressed theoretically [Soft Matter, 2013, 9, 8600-8608]. These authors find that, when the magnetic field is weak, the deflection of the liquid-air interface is static, while for sufficiently strong fields, the interface destabilizes and forms a jet. Motivated by this work, here we develop a numerical model for the closely-related problem of solving two-phase Navier-Stokes equations coupled with the static Maxwell equations. We computationally model the magnetically induced interfacial deflection of a magnetic fluid (ferrofluid) and the transition into a jet by a magnetic field gradient from a permanent magnet. We analyze the shape of the liquid-air interface during the deformation stage and the critical magnet distance, for which the static interface transitions into a jet. We draw conclusions on the ability of our numerical model to predict the large interfacial deformation and the consequent jetting, free of any fitting parameter. [Preview Abstract] |
Monday, November 24, 2014 5:45PM - 5:58PM |
L11.00011: When does aggregation affect magnetic separation? Almut Eisentraeger, Dominic Vella, Ian Griffiths Magnetic separation is an efficient way to remove magnetic and paramagnetic particles suspended in a carrier fluid, and can be used to remove heavy metals from drinking water. Particles are filtered by moving along the gradient of a strong outer magnetic field towards a collection site. Experimental evidence suggests that aggregation of particles to form chains or clusters plays a vital role in determining the efficiency of separation. In diffusion-dominated systems, aggregation may even be required to induce any collection at all. Modelling approaches so far largely consider aggregation in a uniform outer magnetic field, neglecting collective motion, and hydrodynamic interactions between particles and chains. However, long-range hydrodynamic interactions between particles, which gives rise to the concept of hydrodynamic diffusion, have been considered. Here we combine these ideas to investigate how the average velocity and the relative motion of chains and particles during collection influences chain aggregation rates. A one-dimensional model system provides insight into the relative importance of magnetic and hydrodynamic interactions during aggregation and collection, which may be validated by microfluidic experiments. [Preview Abstract] |
Monday, November 24, 2014 5:58PM - 6:11PM |
L11.00012: Three-dimensional microbubble streaming flows Bhargav Rallabandi, Alvaro Marin, Massimiliano Rossi, Christian Kaehler, Sascha Hilgenfeldt Streaming due to acoustically excited bubbles has been used successfully for applications such as size-sorting, trapping and focusing of particles, as well as fluid mixing. Many of these applications involve the precise control of particle trajectories, typically achieved using cylindrical bubbles, which establish planar flows. Using astigmatic particle tracking velocimetry (APTV), we show that, while this two-dimensional picture is a useful description of the flow over short times, a systematic three-dimensional flow structure is evident over long time scales. We demonstrate that this long-time three-dimensional fluid motion can be understood through asymptotic theory, superimposing secondary axial flows (induced by boundary conditions at the device walls) onto the two-dimensional description. This leads to a general framework that describes three-dimensional flows in confined microstreaming systems, guiding the design of applications that profit from minimizing or maximizing these effects. [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. |
© 2022 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
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700