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 HP: Microfluids: Fluidic Devices II |
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Chair: Axel Guenther, University of Toronto Room: Long Beach Convention Center 203A |
Monday, November 22, 2010 10:30AM - 10:43AM |
HP.00001: Use of a porous membrane for gas bubble removal in microfluidic channels: physical mechanisms and design criteria Jie Xu, Regis Vaillant, Daniel Attinger We demonstrate and explain a simple and efficient way to remove gas bubbles from microchannels, by integrating a hydrophobic porous membrane on top of the microchannel. A prototype chip is made in PMMA with the ability to completely filter gas plugs out of a segmented flow at rates up to 7.4 $\mu$L/s/mm$^{2}$. In our device, gas plugs in a water stream are generated continuously from a T-junction and are then transported towards the gas removal section, where they slide along and vent through a hydrophobic membrane. To achieve complete gas removal without membrane leakage, our analysis shows that four necessary operating criteria are needed. These criteria are verified by experimental results. The first criterion is that the bubble length needs to be larger than the channel diameter. The second criterion is that the bubble should stay on the membrane for a time sufficient to transport all the gas through the membrane. The third criterion is that the bubble travel speed should be lower than a critical value: otherwise a stable liquid film between the bubble and the membrane prevents mass transfer. The fourth criterion is that the pressure difference across the membrane should not be larger than the Laplace pressure to prevent water from leaking through the membrane. Experiments on our device show a good agreement with these criteria. [Preview Abstract] |
Monday, November 22, 2010 10:43AM - 10:56AM |
HP.00002: High-speed $\mu$-PTV study of microbubble generation in microfluidic T-junction Ryoji Miyazaki, Toshiyuki Ogasawara, Mitsuhisa Ichiyanagi, Shu Takagi, Yoichiro Matsumoto The bubble generation in a microfluidic T-junction is investigated by high-speed imaging to develop a novel technique for monodispersed microbubble generation. The proposed technique enables generation of 20 $\sim $ 70 $\mu$m diameter bubbles at frequency of 1 $\sim $ 10$^{2}$ kHz, under the mean liquid velocity at the order of 1 m/s. The generation process is quantitatively analyzed focusing the time change of the gas area and the distance between the receding interface and the channel corner. The $\mu$-PTV (micron-resolution Particle Tracking Velocimetry) is operated to measure the flow field on the bubble generation by seeding 1.0 $\mu$m particles with bright-field microscopy. The bubble generation process is highly periodic; therefore, $\mu$-PTV is iteratively conducted in the same phase of the bubble generation. Time-series velocity-vectors at the order of 1 m/s are measured by this high-speed $\mu$-PTV method. The high-speed imaging indicates that the bubble generation consists of two stages; intruding stage and squeezing stage. The terminal gas area is largely determined by the gas area at the beginning of the squeezing stage. According to the obtained flow field, the liquid gradually flows into the side channel with the growth of the gas tip. [Preview Abstract] |
Monday, November 22, 2010 10:56AM - 11:09AM |
HP.00003: Reaction Kinetics in Micro/Nanofluidic Devices: Effect of Confinement and AC Voltage Vishal V.R. Nandigana, Narayana R. Aluru Owing to limited sample consumption, electrokinetic control of convective transport and rapid dissipation of heat, nanofluidic devices are currently being investigated extensively in the field of chemical reactions. The reactants are typically transported into the nanochannel by using external DC electric fields. In this study, a novel technique to increase the rate of catalytic reactions inside nanofluidic devices is presented. Specifically, the effect of combined AC and DC electric fields on different reaction kinetics was numerically investigated and it was found to enhance the rate of formation of desired species in reaction limited kinetics (when the Damk\"{o}hler number (Da) $\le $ 1). We investigate the role of AC frequency, amplitude, channel height and surface charge density on reaction kinetics. We develop analytical expressions for fluid transport under combined AC and DC fields and also develop expressions to identify optimal frequencies. Several examples are considered to illustrate the effect of AC fields on chemical reactions in nanochannels. [Preview Abstract] |
Monday, November 22, 2010 11:09AM - 11:22AM |
HP.00004: Melt Crystallization in Microfluidics for Sample Concentration Pooria Sharif-Kashani, H. Pirouz Kavehpour Melt crystallization in microfluidics is a novel approach to concentrate/purify a diverse range of samples from particles to ions. In this technique, the difference in solubility of solutes in the liquid and solid phase of the solvent drives the transport of the solutes. Consequently, this method has the advantage of being non-invasive and entirely thermally-actuated with no moving parts. A fluid sample is frozen in a microchannel and melting zones are passed repeatedly through the stationary sample to increase the concentration of solute at one end. The device is constructed using a thermoelectric cooler to freeze the sample and thin-film resistive heaters to create melting zones. The heaters are operated independently, allowing them to be switched on or off to create a localized melting zone in the channel. The performance of the system is successfully tested for a variety of samples including aqueous solutions and water containing micro-particles. [Preview Abstract] |
Monday, November 22, 2010 11:22AM - 11:35AM |
HP.00005: Charge Transport Behavior in Microfluidic Microbial Energy Conversion Devices Aloke Kumar, Partha Mukherjee, Abhijeet Borole, Mitchel Doktycz Microbial energy harvesting devices utilize anode-respiring bacteria (ARB), present as a biofilm matrix, to generate electrical current from organic matter. The conductive biofilm matrix in the anode compartment plays a key role in the overall charge transport behavior. Especially, biofilm kinetics and ARB community dynamics are of paramount importance influencing the anode overpotential, which is further dependent on the pH variation. In this work, we present a theoretical framework to study the charge transport characteristics with concomitant biofilm kinetics, substrate utilization, diffusion and migration in a microfluidic device with microbial energy generation. [Preview Abstract] |
Monday, November 22, 2010 11:35AM - 11:48AM |
HP.00006: Transporting Microparticles Using a Conveyor Belt of Artificial Cilia Amitabh Bhattacharya, Gavin Buxton, Alexander Alexeev, O. Berk Usta, Anna C. Balazs We present results from simulations of particle transport in a fluid microchannel via a regular array of actuated cilia. For each cilium, one end is tethered to the wall, while the other end is actuated by an external periodic force. This leads to a time-asymmetric, cyclic motion for each cilium. We study the motion of a microparticle in the fluid due to the cilia actuation. An adhesive force between the particle and cilia enables a transport mechanism for the particle in which the particle is passed from one cilium to the next cilium in the array. The particle is also dragged forward by flow in the channel, induced by the time-asymmetric motion of the cilia. The simulations are performed using the Lattice Boltzmann Method for the flow, with a chain of point-forces, connected by springs, used to represent each cilium. We will present the parameter regime where the most effective transport of the particle occurs due to the combination of cilia-particle adhesion and fluid motion. [Preview Abstract] |
Monday, November 22, 2010 11:48AM - 12:01PM |
HP.00007: Induced-Charge Electro-Osmosis Micropumps for Portable Microfluidics: theory and experiment Joel Paustian, Todd Squires Microfluidic devices (e.g. Labs on a Chip) are becoming useful scientific and medical tools for automating chemical and biological lab work. Various impediments prevent complex microfluidic devices from being easily removed from a laboratory setting, limiting their utility for day-to-day applications like in-the-field medical diagnostics and drug delivery. The development of portable and integrable high-pressure pumping techniques will be necessary step for truly portable, complex microfluidic devices. Microfluidic pumps based on the electrokinetic phenomenon of Induced-Charge Electro-Osmosis (ICEO) could potentially fill this role. We describe ICEO and present a simple idea for a low-voltage, high-pressure micropump. We give simple scaling arguments, and a detailed theory, for its expected performance, and describe the design, fabrication, testing and characterization of a functional ICEO micropump. Our results validate the central idea, are consistent with our theoretical expectations, and suggest routes for the optimization and eventual use of the pump. [Preview Abstract] |
Monday, November 22, 2010 12:01PM - 12:14PM |
HP.00008: Regulating flow with substrate shape in capillary micropumps Matthew Hancock, John Bush Capillarity offers a passive mechanism to pump fluid through portable lab-on-a-chip systems, making them ideal for rapid in situ analysis of medical samples in the developing world. A common capillary micropump design is powered by the difference in curvature pressures between drops at the inlet and outlet of a microchannel. The resulting flow rate is transient, depending on the geometry of the inlet cavity and the instantaneous droplet volumes. We here present a class of microcavity shapes that maintain constant pressure within droplets regardless of their volumes. This special class of microcavities may prove useful for regulating pressure in microfluidic devices. We suggest the design of a passive capillary micropump fitted with a special pressure regulating inlet cavity that forces a constant flux through a microchannel. The influence of gravity on this class of microcavities is considered. [Preview Abstract] |
Monday, November 22, 2010 12:14PM - 12:27PM |
HP.00009: Pumping of Dielectric Liquids Using Non-Uniform-Field Induced Electrohydrodynamic Flow Jae Chun Ryu, Wonkyoung Kim, Kwan Hyoung Kang Pumping of dielectric liquids or poorly conducting liquids is necessary in cooling of microelectronic devices, dispensing liquids in miniature systems for chemical and biological analysis, and micropumping of organic solvents for microreactor. Electrical pumping of liquids is more attractive than conventional mechanical pumping methods because of many advantages such as simple design, no mechanical parts, low acoustic noise, and lightweight. We present a new electrohydrodynamic (EHD) pumping method for dielectric liquids. The pumping method relies on the EHD flow generated by electric-field dependent electrical conductivity (Onsager effect). A polar additive plays an important role in enhancing the field-dependency of conductivity. When ac voltage is applied, a fast and regular flow was produced around electrodes. Flow speed is proportional to cube of electric-field strength and inversely to applied frequency. The experimental results showed good agreement with numerical analysis which is based on our model. [Preview Abstract] |
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