Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session LP: Microfluids: Fluidic Devices III |
Hide Abstracts |
Chair: Alexander Alexeev, Georgia Institute of Technology Room: Long Beach Convention Center 203A |
Monday, November 22, 2010 3:35PM - 3:48PM |
LP.00001: Temperature-Controlled Free-Surface Microfluidic Devices Meysam Barmi, Brian Piorek, Chrysafis Andreou, Carl Meinhart Free-Surface MicroFluidics (FSMF) have recently received much attention for their applications especially their ability for airborne chemical detection [Piorek, 2007]. Surface tension is generally used for fluid transport through microchannels in FSMF; however, it is not simply controllable. Thus, evaporation can be utilized for the flow control. In the current study, temperature-controlled microvalves are developed to control the fluid flow in FSMF by evaporation. The microvalve controls the flow by changing the surface temperature and requires a few tenths of a second to operate. The operating time depends on the temperature and microvalve geometry. Therefore, several configurations were fabricated and tested to find the most sensitive microvalve with the least leakage. The microchannels were fabricated on Silicon substrates with built-in heaters and RTD sensors to provide the desired temperature for microvalve operation. The high speed camera was employed to measure the operating time and velocity field. Moreover, numerical simulations were carried out by COMSOL multiphysics to find the velocity field versus the applied heat flux. They had a good agreement with the experimental results. [Preview Abstract] |
Monday, November 22, 2010 3:48PM - 4:01PM |
LP.00002: Detection of Yeast Cells; Microfluidic Impedance Sensor Kelsey Hulea, Nicholas Matune, Benjamin Mabbott, Yogendra Panta A microelectromechanical system (MEMS) based biosensor was proposed for the rapid detection of pathogenic bacteria and contaminants that pose a threat to public health. In this study, experimental tests followed by finite element computer simulations were performed to selectively detect the quantity of yeast cells in a sample solution then was compared to a solution with no yeast cells. The impedance based biosensor detects the change in impedance caused by the presence of yeast cells between the electrodes integrated into microchannel walls that contain the target cells in a suspension medium. Microfluidic devices were fabricated by using two methods: traditional micromachining and photolithography for experimental purposes. An impedance analyzer was experimentally used for the measurement of the electrical impedance signals. Computer models based in COMSOL Multiphysics consisted of a long microchannel with two electrodes placed on opposite sides of the channel. Experimental data, simulation results and published data were compared and similar trends were found. [Preview Abstract] |
Monday, November 22, 2010 4:01PM - 4:14PM |
LP.00003: Nanoaquarium for Imaging Processes in Liquids with Electrons Joseph Grogan, Haim Bau The understanding of many nanoscale processes occurring in liquids such as colloidal crystal formation, aggregation, nanowire growth, electrochemical deposition, and biological interactions would benefit greatly from real-time, in-situ imaging with the nanoscale resolution of the transmission electron microscopes (TEMs) and scanning transmission electron microscopes (STEMs). However, these imaging tools cannot readily be used to observe processes occurring in liquid media without addressing two experimental hurdles: sample thickness and sample evaporation in the high vacuum microscope chamber. To address these challenges, we have developed a nano-Hele-Shaw cell, dubbed the nanoaquarium. The device consists of a hermetically-sealed, tens of nanometers tall, liquid-filled chamber sandwiched between two freestanding, 50 nm thick, silicon nitride membranes. Embedded electrodes are integrated into the device for sensing and actuation. To demonstrate the device's capabilities, we imaged diffusion-limited aggregation of 5nm diameter, gold nanoparticles. The rate of aggregation and the fractal dimension of the aggregate are consistent with light scattering measurements, indicating that the electron beam does not greatly alter the observed phenomenon. [Preview Abstract] |
Monday, November 22, 2010 4:14PM - 4:27PM |
LP.00004: Numerical analysis of a fluidic oscillator Stefan Hoettges, Torsten Schenkel, Herbert Oertel The technology of fluid logic or fluidic has its origins in 1959 when scientists were looking for alternatives to electronics to realize measuring or automatic control tasks. In recent years interest in fluidic components has been renewed. Possible applications of fluidic oscillators have been tested in flow control, to reduce or eliminate separation regions, to avoid resonance noise in the flow past cavities, to improve combustion processes or for efficient cooling of turbine blades or electronic components. The oscillatory motion of the jet is achieved only by suitable shaping of the nozzle geometry and fluid-dynamic interactions, hence no moving components or external sources of energy are necessary. Therefore fluidic oscillators can be used in extreme environmental conditions, such as high temperatures, aggressive media or within electromagnetic fields. In the present study the working principle of the fluidic oscillator has been identified using three-dimensional unsteady RANS simulations and stability analysis. The numerical models used have been validated successfully against experimental data. Furthermore the effects of changes in inlet velocity, geometry and working fluid on the oscillation frequency have been investigated. Based on the results a new dimensionless number has been derived in order to characterize the unsteady behavior of the fluidic oscillator. [Preview Abstract] |
Monday, November 22, 2010 4:27PM - 4:40PM |
LP.00005: Microfluidic strategy to investigate dynamics of small blood vessel function Sanjesh Yasotharan, Steffen-Sebastian Bolz, Axel Guenther Resistance arteries (RAs, 30-300 microns in diameter) that are located within the terminal part of the vascular tree regulate the laminar perfusion of tissue with blood, via the peripheral vascular resistance, and hence controls the systemic blood pressure. The structure of RAs is adapted to actively controlling flow resistance by dynamically changing their diameter, which is non-linearly dependent on the temporal variation of the transmural pressure, perfusion flow rate and spatiotemporal changes in the chemical environment. Increases in systemic blood pressure (hypertension) resulting from pathologic changes in the RA response represent the primary risk factor for cardiovascular diseases. We use a microfluidic strategy to investigate small blood vessels by quantifying structural variations within the arterial wall, RA outer contour and diameter over time. First, we document the artery response to vasomotor drugs that were homogeneously applied at step-wise increasing concentration. Second, we investigate the response in the presence of well-defined axial and circumferential heterogeneities. Artery per- and superfusion is discussed based on microscale PIV measurements of the fluid velocity on both sides of the arterial wall. Structural changes in the arterial wall are quantified using cross-correlation and proper orthogonal decomposition analyses of bright-field micrographs. [Preview Abstract] |
Monday, November 22, 2010 4:40PM - 4:53PM |
LP.00006: Microfluidic waves for flow control Hossein Haj-Hariri, Marcel Utz, Matthew Begley The propagation of coupled waves in fluidic channels with elastic covers is discussed in view of applications for flow control in microfluidic devices. A theory is developed for pressure waves in the fluid coupled to bending waves in the elastic cover. At low frequencies, the lateral bending of the cover dominates over longitudinal bending, leading to propagating, non-dispersive longitudinal pressure waves in the channel. The theory addresses effects due to both the finite viscosity and compressibility of the fluid. The coupled waves propagate without dispersion, as long as the wave length is larger than the channel width. It is shown that in channels of typical microfluidic dimensions, wave velocities in the range of a few 10 m/s result if the channels are covered by films of a compliant material such as PDMS. The application of this principle to design microfluidic band pass and band stop filters based on standing waves is discussed. Characteristic frequencies in the range of a few kHz are readily achieved with quality factors above 30. [Preview Abstract] |
Monday, November 22, 2010 4:53PM - 5:06PM |
LP.00007: A Portable, Air-Jet-Actuator-Based Device for System Identification Wayne Staats, Jesse Belden, Anirban Mazumdar, Ian Hunter System identification (ID) of human and robotic limbs could help in diagnosis of ailments and aid in optimization of control parameters and future redesigns. We present a self-contained actuator, which uses the Coanda effect to rapidly switch the direction of a high speed air jet to create a binary stochastic force input to a limb for system ID. The design of the actuator is approached with the goal of creating a portable device, which could deployed on robot or human limbs for in situ identification. The viability of the device is demonstrated by performing stochastic system ID on an underdamped elastic beam system with fixed inertia and stiffness, and variable damping. The non-parametric impulse response yielded from the stochastic system ID is modeled as a second order system, and the resultant parameters are found to be in excellent agreement with those found using more traditional system ID techniques. The current design could be further miniaturized and developed as a portable, wireless, on-site multi-axis system identification system for less intrusive and more widespread use. [Preview Abstract] |
Monday, November 22, 2010 5:06PM - 5:19PM |
LP.00008: A hybrid molecular dynamics study of the translocation of DNA through entropic traps Petr Hotmar The interplay between thermal diffusion and electrophoretic migration of $\lambda$-phage DNA in entropic traps was studied using a hybrid molecular dynamics algorithm. The governing systems of field equations are discretized by finite differences on curvilinear overlapping grids with the solvent modeled as a continuum in unsteady creeping flow. Similar to Brownian dynamics, the polymer segments are coarse-grained into a bead-spring model that follows Langevin dynamics. The hydrodynamic interactions are captured on a semi-empirical level with localized force-transfer. We have established the non-monotonic dependence of electrophoretic mobility on chain length, which characterizes the transition from the free flowing to the trapping behavior. We further quantify the subtle effects of dielectrophoresis and induced-charge electroosmosis on the polymer dynamics. [Preview Abstract] |
Monday, November 22, 2010 5:19PM - 5:32PM |
LP.00009: Microfluidic assembly of multiscale soft materials Lian Leng, Axel Guenther The vast majority of materials found in nature are characterized by length scales that span several orders of magnitude. Material properties such as porosity, permeability and elasticity are therefore locally and directionally tuned to their (biological) function and adapted to local environmental conditions. We use a massively scaled microfluidic approach to synthetically define multiscale complex fluids and soft materials with precisely tunable, non-isentropic bulk properties. Two or more fluids are separately introduced to the device that consists of fifteen vertically bonded and fluidically connected substrate layers, and guided to an exit section that either consists of 23 equidistantly spaced channels or a 23 x 15 channel array. The flow rates through individual channels are computer-controlled. Upon entering a reservoir in a flow-focusing configuration, a spatially organized fluid with characteristic length scales of 250 microns and 10 mm was defined, and retained via a chemical reaction. To illustrate different soft material morphologies in one, two or three directions, we demonstrate the formation of isolated fibers (1D); planar graded and barcoded materials (2D); graded bulk materials and perfusable matrices (3D). [Preview Abstract] |
Monday, November 22, 2010 5:32PM - 5:45PM |
LP.00010: Free-surface digital microfluidic systems for optimized SERS analysis in gas chromatography Brian Piorek, Chrysafis Andreou, Seung Joon Lee, Martin Moskovits, Carl Meinhart A gas/liquid digital microfluidic platform was developed to chemically analyze gaseous analyte streams eluting from separation columns common in gas chromatography. The digital microfluidic stream is comprised of compartmentalized gaseous eluent packets segmented by SERS-active nanoparticles which are suspended within an aqueous phase. The microfluidic system is designed to optimize gaseous analyte transport into the SERS-active phase for chemical detection and analysis. Microfluidic and gas-phase flow patterns are controlled to produce reliable nanoparticle aggregation, resulting in SERS hot spots responsible for the PPT-level gas analysis mechanism. Since the flowing eluent is packetized by aqueous partitions, its spatiotemporal location can be controlled for effective analysis by SERS of nanoparticle hot-spot clusters occurring within individual partitions. [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