Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session AA: Micro Fluids: Fluidic Devices I |
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Chair: Kamran Mohseni, University of Colorado, Boulder Room: Salt Palace Convention Center 150 A-C |
Sunday, November 18, 2007 8:30AM - 8:43AM |
AA.00001: Fast Microfluidic Actuation Using Surface Wave Vibrations Ming Tan, James Friend, Leslie Yeo The propagation of surface waves along a piezoelectric substrate are employed to generate inertial liquid streaming and hence rapid and efficient microfluidic actuation. We demonstrate this mechanism for two cases, namely, an open microfluidic platform and a closed microchannel system. In the first, drops are swept across a hydrophobic track patterned above the substrate. We also show that this is a useful tool for collecting and concentrating microparticles, and in particular biological particles, for biological sampling, detection and analysis, and, environmental monitoring. In the second case, the streaming flow arising from the surface vibrations along the sidewalls of a 30 micron wide and 100 micron deep microchannel is observed to give rise to throughflow with volumetric flowrates of the order 1 microlitre/min, thus constituting an effective fluid-driving mechanism in closed microfluidic devices. [Preview Abstract] |
Sunday, November 18, 2007 8:43AM - 8:56AM |
AA.00002: Modeling Patterned Substrates that Selectively Entrap and Burst Microcapsules Alexander Alexeev, Anna C. Balazs To optimize the efficient operation of microfluidic devices, there is a need for micro-carriers that can be readily directed to specific locations within microchannels and made to release their contents in a prescribed manner. Compliant microcapsules constitute ideal micro-carriers since both their chemical and mechanical properties can be tailored, providing distinct keys for regulating their behavior. Using computational modeling, we lay out chemically patterned substrates that exploit these distinctive features and thereby selectively route specific capsules to specified locations, drive these capsules to burst and thus, deliver their payload in a ``programmable'' manner. The findings reveal that an ``instruction set'' can be encoded into the system by coupling the physicochemical properties of the microcapsules and the substrates. These instructions are dynamically deciphered during the operation of the device, so that the system can perform a number of functions in an autonomous manner. This approach opens up new strategies for designing smart microfluidic devices. [Preview Abstract] |
Sunday, November 18, 2007 8:56AM - 9:09AM |
AA.00003: The Pressure Drop along Rectangular Microchannels Containing Bubbles Ann Lai, Michael Fuerstman, Meghan Thurlow, Sergey Shevkoplyas, Howard Stone, George Whitesides We derive the drop in pressure along a rectangular microchannel through which a flowing liquid (water, with or without surfactant, and mixtures of water and glycerol) carries bubbles. We use an indirect method to derive the pressure in the channel. At both low and high concentrations of surfactant, the pressure drop depends predominantly on the number of bubbles in the channel. At intermediate concentrations of surfactant, the total, aggregated length of the bubbles in the channel is the dominant contributor to the pressure drop. The difference between these two cases stems from the flow of liquid through the ``gutters'' -- the regions of the system bounded by the curved body of the bubble and the corners of the channel -- in the presence of intermediate concentrations of surfactant. We present a systematic and quantitative investigation of the influence of surfactants on such multiphase flows in rectangular microchannels. We surmise that the contributions to the overall pressure drop stem from three regions: i) the slugs of liquid, where the liquid flows as if no bubbles were present; ii) the ``gutters'' running alongside the body of the bubble; and iii) the curved caps at the ends of the bubble. [Preview Abstract] |
Sunday, November 18, 2007 9:09AM - 9:22AM |
AA.00004: Micro-capillary aerosol focusing device: theoretical modeling, experimental verification, and device fabrication. Justin Hoey, Iskander Akhatov, Orven Swenson, Doug Schulz A theoretical model for the focusing of aerosol particles in a linearly-varying micro-capillary with a diameter on the order of 100 microns is presented. This theoretical model is experimentally verified by visualizing an aerosol beam of silver-ink aerosol particles of approximately 1 micron in diameter emitted from a micro-capillary. Additional validation is presented in the deposited lines where linewidth is a function of aerosol beamwidth. From the theoretical model a new design for the focusing of aerosol particles is developed, physically produced, and experimentally validated. The new device will be implemented in the areas of high frequency RFID manufacturing, and the semiconductor industry. [Preview Abstract] |
Sunday, November 18, 2007 9:22AM - 9:35AM |
AA.00005: A Numerical Study on Drop Formation in Flow-Focusing Microfluidic Devices Jing Lou, Baili Zhang, Jinsong Hua Generation of mono-dispersed droplets in microfluidic devices using ``flow-focusing'' arrangement has received intensive interest due to its geometrical simpleness and easiness in controlling the droplet size by adjusting the flow rate of continuous phase. Experiments have shown that there are two kinds of droplet generation modes, namely dripping mode and jetting mode, the droplet sizes formed in these two modes varies sharply when the mode transition occurs. CFD based multiphase-flow simulation is applied to investigate drop formation pattern in the flow focusing micro channel in this study. The focus is on the effect of the flow focusing channel geometry, especially the expansion angle from the nozzle to collection tube, on the droplet size and the formation modes. It is found that channel geometry has significant effect on the droplet size and formation mode. Reducing expansion angle leads to the decrease of droplet size and hence the increase of drop formation frequency. The most interesting finding is that when the flow rate of the continuous phase increases, the transition point from dripping mode to jetting mode is also shifted as a result of reducing expansion angle. The simulation results will help us not only to understand the mechanism of droplet, but also to improve the flow focusing channel design to produce monodisperse droplets with minor effects from droplet generation mode transition. [Preview Abstract] |
Sunday, November 18, 2007 9:35AM - 9:48AM |
AA.00006: Digitized Heat Transfer Kamran Mohseni, Patrick Young This presentation presents theoretical and numerical results describing digitized heat transfer (DHT), an active thermal management technique for high-power electronics and integrated micro systems. In digitized heat transfer discrete droplets are employed. The internal flow inside a discrete droplet is dominated by internal circulation imposed by the boundaries. This internal circulation imposes a new timescale for recirculating cold liquid from the middle of the droplet to the boundary. This internal circulation produces periodic oscillation in the overall convective heat transfer rate. Numerical simulations are presented for heat transfer in the droplet for both constant temperature and flux boundary conditions. The effectiveness of DHT for managing both localized temperature spikes and steady state cooling is demonstrated, identifying key parameters for optimization of the DHT method. [Preview Abstract] |
Sunday, November 18, 2007 9:48AM - 10:01AM |
AA.00007: Dispersion in microfluidic separation systems in presence of wall interactions and axial inhomogeneites Subhra Datta, Sandip Ghosal The dispersion of a solute which undergoes adsorption and desorption on the walls of a straight microchannel of axially varying cross-section is studied, motivated by capillary electrophoresis and chromatographic applications. An asymptotic approach based on the long time limit is adopted, which leads to the formulation of a model that requires the solution of only one-dimensional partial differential equations. As a check of accuracy of the asymptotic results, the full three-dimensional equations governing the transport and adsorption-desorption of the solute in a rectangular microchannel are solved numerically under axially variable and axially invariant electroosmotic flow fields and the results are compared to those from the asymptotically reduced model. The asymptotically reduced model gives accurate predictions for both slow and fast adsorption-desorption processes, unlike results from the theory of band broadening in chromatographic processes, which, incidentally emerge as a special case of the model. [Preview Abstract] |
Sunday, November 18, 2007 10:01AM - 10:14AM |
AA.00008: Fluid Flow and Heat Transfer in a Dual-wet Micro Heat Pipe Jin Zhang, Stephen Watson, Harris Wong Micro heat pipes have been used to cool micro electronic devices, but their heat transfer coefficients are low compared with those of conventional heat pipes. In this talk, a dual-wet pipe is proposed as a model to study heat transfer in micro heat pipes. The dual-wet pipe has a long and narrow cavity. The bottom-half of the horizontal pipe is made of a wetting material and holds a wetting liquid, whereas the top-half is made of a non-wetting material and is filled with the vapor. As one end of the pipe is heated, the liquid evaporates and increases the vapor pressure. The higher pressure drives the vapor to the cold end where the vapor condenses and releases the latent heat. The condensate moves along the bottom half of the pipe back to the hot end to complete the cycle. Hence, the heat pipe is driven by the difference in equilibrium vapor pressure between the hot and cold ends, and not by the liquid-vapor interfacial curvature as is commonly believed. Our analysis provides an explanation for the comparatively low effective thermal conductivity in micro heat pipes [1]. \newline \newline [1] Zhang, Watson {\&} Wong, J. Fluid Mech. (2007, in press) [Preview Abstract] |
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