Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session R30: Microfluids: Microchannels |
Hide Abstracts |
Chair: Sangjin Ryu, University of Nebraska, Lincoln Room: 408 |
Tuesday, November 26, 2013 1:05PM - 1:18PM |
R30.00001: Noninvasive Measurement of the Pressure Distribution in a Deformable Micro-Channel Ozgur Ozsun, Victor Yakhot, Kamil L. Ekinci Direct and noninvasive measurement of the pressure drop in test sections of a rigid micro-channel is a challenging task. In a micro-channel with compliant walls, however, it is possible to determine the pressure field under flow from the local deflection of the channel walls. Here, we present a robust analytical approach for determining the pressure distribution in a deformable micro-channel under flow. In this method, we first measure the channel deflection profile as a function of applied hydrostatic pressure; this initial measurement provides the constitutive curves for the deformable channel. We then match the deflection profile under flow to the constitutive curves, obtaining the hydrodynamic pressure distribution. We have tested and validated the developed mapping on planar micro-fluidic channels. This method remains accurate in a broad parameter space, and can find possible applications in microfluidics and for characterizing biological flows. [Preview Abstract] |
Tuesday, November 26, 2013 1:18PM - 1:31PM |
R30.00002: Flow rate--pressure drop relation for deformable shallow microfluidic channels Ivan C. Christov, Vincent Cognet, Howard A. Stone Laminar flow in devices fabricated from PDMS causes deformation of the passage geometry, which affects the flow rate--pressure drop relation. Having an accurate flow rate--pressure drop relation for deformable microchannels is of importance given that the flow rate for a given pressure drop can be as much as 500\% of the flow rate predicted by Poiseuille's law for a rigid channel. Gervais et al.\ [{\it Lab Chip} {\bf 6} (2006) 500] proposed a successful model of the latter phenomenon by heuristically coupling linear elasticity with the lubrication approximation for Stokes flow. However, their model contains a fitting parameter that must be found for each channel shape by performing an experiment. We present a perturbative derivation of the flow rate--pressure drop relation in a shallow deformable microchannel using Kirchoff--Love theory of isotropic quasi-static plate bending and Stokes' equations under a ``double lubrication'' approximation (i.e., the ratio of the channel's height to its width and of the channel's width to its length are both assumed small). Our result contains no free parameters and confirms Gervais et al.'s observation that the flow rate is a quartic polynomial of the pressure drop. [Preview Abstract] |
Tuesday, November 26, 2013 1:31PM - 1:44PM |
R30.00003: Shear and Pressure Driven Flow in Microchannels Yogesh Jaluria In many important circumstances, microchannel flows driven by moving surfaces that impart shear to the fluid and by an imposed pressure difference across the channel are of interest. The pressure may aid or oppose the flow due to the moving surface. One such problem is the optical fiber coating process, where the entrance of the moving fiber into a reservoir of fluid, as well as its exit, results in shear driven flow in microchannels. An additional aiding or opposing pressure head is also usually applied. The transport processes influence the resulting coating very substantially. This paper discusses the basic considerations that arise in such processes, particularly the resulting flow and the menisci that are observed at the inlet and outlet regions of the two microchannels. Visualization has been an important approach to the basic understanding of these flows. Detailed flow and thermal transport results are often obtained by numerical modeling. Another important circumstance is the pressure rise in the channel for narrowing flow domains, such as those employed in dies and extruders. It is found that, in practical problems, high pressures are generated that oppose the shear effects. Then the resulting transport is affected by both shear and pressure. On the other hand, cooling of electronic systems often employs pressure-driven microchannel flows. Comparisons between the results obtained for these different flow situations indicate many interesting features, which are discussed in terms of the basic mechanisms. [Preview Abstract] |
Tuesday, November 26, 2013 1:44PM - 1:57PM |
R30.00004: Momentum and mass transport over a superhydrophobic bubble mattress: the influence of interface geometry Peichun Amy Tsai, A. Sander Haase, Elif Karatay, Rob Lammertink We numerically investigate the influence of interface geometry on momentum and mass transport on a partially slippery bubble mattress. The bubble mattress, forming a superhydrophobic substrate, consists of an array of slippery (shear-free) gas bubbles with (no-slip) solids walls in between. We consider steady pressure-driven laminar flow over the bubble mattress, with a solute being supplied from the gas bubbles. The results show that solute transport can be enhanced significantly due to effective slippage, compared to a fully saturated no-slip wall. The enhancement depends on the interface geometry of the bubble mattress, i.e. on the bubble size, protrusion angle, and surface porosity. In addition, we demonstrate that the mass transfer enhancement disappears below a critical bubble size. The effective slip vanishes for very small bubbles, whereby interfacial transport becomes diffusion dominated. For large bubbles, solute transport near the interface is greatly enhanced by convection. The results provide insight into the optimal design of ultra-hydrophobic bubble mattresses to enhance both momentum and mass transport. [Preview Abstract] |
Tuesday, November 26, 2013 1:57PM - 2:10PM |
R30.00005: ABSTRACT WITHDRAWN |
Tuesday, November 26, 2013 2:10PM - 2:23PM |
R30.00006: Spontaneous oscillations in simple fluid networks Deborah Hellen, Erika Weiler, Nathan Karst, John Geddes, Brian Storey Nonlinear phenomena including multiple equilibrium states and spontaneous oscillations can occur in fluid networks containing multiple fluid phases. Such behavior might be attributed to the complicated geometry of the network, the complex rheology of the constituent fluids, or, in the case of microvascular blood flow, biological control. However, the simplest networks containing two miscible Newtonian fluids of differing viscosities are found to exhibit these non-linear phenomena. We use a combination of analytic and numerical techniques to identify and track saddle-node and Hopf bifurcations through the large parameter space. The model predictions show regions of sustained spontaneous oscillations and we investigate the sensitivity of these oscillations to changes in the viscosity contrast and network geometry. The model predictions are used to guide ongoing experimental which has confirmed the existence of such oscillations. [Preview Abstract] |
Tuesday, November 26, 2013 2:23PM - 2:36PM |
R30.00007: Developing and testing models for flow in microdevices Laura Dickinson, Jonathan Kobine Microtechnology has developed faster than the corresponding theory describing the physics behind it. The continuum assumptions of classical fluid mechanics break down at the smallest lengthscales; however, Stokes and Poiseuille flow applies for liquid flow in microchannels, and there is merit in using the Navier-Stokes equations as a starting point from which accurate yet parsimonious models of flow in microdevices can be developed. We derive such models for the pressure drop across and the flux through a generic 2D microvalve, which show how each varies with valve opening (the characteristic curve). Eg, the nondimensional pressure drop $P$ in terms of scaled valve opening $H$ can be expressed as \[ P=1-2\frac{(1-H^{6})^{\frac{1}{2}}-1}{H^{6}}. \] We verify these models using a finite-element Navier-Stokes solver. Valves with a ``long seat'' and laminar flows are modeled accurately. We make additions to our models to capture the effects of flow at higher Re. The results of our simulations highlight flow behavior which is interesting to practitioners in the field of applied microfluidics; sharp valve edges produce separation and recirculation, small valve openings produce two jets which recombine in the valve exit. These phenomena give rise to the (turbulent) mixing which is desired but not easily achieved in microdiagnosics. [Preview Abstract] |
Tuesday, November 26, 2013 2:36PM - 2:49PM |
R30.00008: On the Effects of 3D Field Focusing at a Heterogeneous Permselective Surface on Concentration Polarization Yoav Green, Gilad Yossifon Understanding the effects of 2D and 3D geometric field focusing effects at the interface of a microreservoir-nanochannel system is of much importance in the growing field of electrokinetics and microfluidics. Such effects have been used in numerous and varying experimental systems but little theoretical work has been conducted to better understand these effects quantitatively. Previous studies made a number of oversimplifying assumptions regarding the geometry of the microreservior and its effects on concentration polarization so that the solution was valid only at certain limits. A 3D analytical solution is derived for the concentration and electric potential for an electrolyte undergoing concentration polarization. The effects of the both the microreservoir's and the permselective interface's geometry are investigated. It is shown that limiting current transported through the permselective surface is not only a function of the area but is strongly geometry dependent (i.e. rectangular or square surface). Additionally, it is shown that there is an amplification of the current density with increased field focusing effects which stands in agreement with previous experimental results. [Preview Abstract] |
Tuesday, November 26, 2013 2:49PM - 3:02PM |
R30.00009: The role of erythrocyte size and shape in microchannel fluid dynamics Kathryn Fink, Jacobo Paredes, Dorian Liepmann The unique properties of blood flow in microchannels have been studied for nearly a century; much of the observed blood-specific dynamics is attributed to the biconcave shape of red blood cells. However, for almost twice as long biologists have observed and characterized the differences in the size and shape of red blood cells among vertebrates. With a few exceptions, mammals share the denucleated biconcave shape of erythrocytes but vary in size; oviparous vertebrates have nucleated ovoid red blood cells with size variations of a full order of magnitude. We utilize micro-PIV to analyze blood flow of vertebrate species in microchannels, with a focus on understanding how erythrocyte size and shape alter the cell-free layer and velocity profile of whole blood. The results offer insight into the Fahraeus-Lindqvist effect and the selection of animal blood for the design and evaluation of biological microfluidic devices. [Preview Abstract] |
Tuesday, November 26, 2013 3:02PM - 3:15PM |
R30.00010: Deformations of micro-capsules through channels with corners Luca Brandt, Lailai Zhu Deformable micro-particles moving in confined geometries are ubiquitous in nature from biological cells to biomedical and industrial applications such as synthetic capsules. Previous studies have demonstrated rich and complex behaviors of capsules and vesicles in the $2$D Poiseuille flow, in a duct and in a pipe. Nevertheless, micro-particles commonly need to go through asymmetric geometries, for example a corner. Here we numerically study the dynamics of a Neo-Hookean capsule transported in a $3$D channel with a $90$ degree straight corner. We use the boundary integral method to solve the Stokes flow, accelerated by the general geometry Ewald method (GGEM) implemented in the framework of the general Navier-Stokes solver NEK5000 based on the spectral element method. A global spectral description utilizing spherical harmonics is incorporated to resolve simultaneously the membrane dynamics. We analyze the trajectory and deformation of the capsule, as well as the variation of area, velocity, principle stress and elastic energy. The influence of the capsule elasticity and wall confinement is also investigated. Finally, the flow in a smooth corner is simulated and compared with the straight counterpart, to provide hints for the design of micro-devices. [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