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 M10: Microscale Flows: General |
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Chair: Carl Meinhart, University of California, Santa Barbara Room: 3005 |
Tuesday, November 25, 2014 8:00AM - 8:13AM |
M10.00001: Control of microparticles packing density in a microfluidic channel for bead based immunoassays applications Gabriel Caballero-Robledo, Pablo Guevara-Pantoja Bead based immunoassays in microfluidic devices have shown to greatly outperform conventional methods. But if functional point-of-care devices are to be developed, precise and reproducible control over the granulate packings inside microchannels is needed. In this work we study the efficiency of a nanoparticles magnetic trap previously developed by B. Teste et al. [Lab Chip 11, 4207 (2011)] when we vary the compaction of micrometric iron beads packed against a restriction inside a microfluidic channel. The packing density of the beads is finely and reproducibly changed by applying a vibrational protocol originally developed for macroscopic, dry granular systems. We find, counterintuitively, that the most compact and stable packings are up to four times less efficient in trapping nano particles than the loosest packings. [Preview Abstract] |
Tuesday, November 25, 2014 8:13AM - 8:26AM |
M10.00002: Salmonella capture using orbiting magnetic microbeads Drew Owen, Matthew Ballard, Zachary Mills, Srinivas Hanasoge, Peter Hesketh, Alexander Alexeev Using three-dimensional simulations and experiments, we examine capture of salmonella from a complex fluid sample flowing through a microfluidic channel. Capture is performed using orbiting magnetic microbeads, which can easily be extracted from the system for analysis after salmonella capture. Numerical simulations are used to model the dynamics of the system, which consists of a microchannel filled with a viscous fluid, model salmonella, magnetic microbeads and a series of angled parallel ridges lining the top of the microchannel. Simulations provide a statistical measure of the ability of the system to capture target salmonella. Our modeling findings guide the design of a lab-on-a-chip experimental device to be used for the detection of salmonella from complex food samples, allowing for the detection of the bacteria at the food source and preventing the consumption of contaminated food. Such a device can be used as a generic platform for the detection of a variety of biomaterials from complex fluids. [Preview Abstract] |
Tuesday, November 25, 2014 8:26AM - 8:39AM |
M10.00003: Programmable Electro Osmotic Lab on a Chip Andreas G. Class We propose to use a 2D check-board patterned surface with alternating zeta potential made of semiconductors and individually controllable electrodes surrounding each field to drive by electro osmosis an arbitrary flow along the surface within the cavity of a lab-on-a-chip. In contrast to other fluid mechanic devices the flow is not driven by pressure gradients but rather by a controllable fluid velocity within the Debay boundary layer. Thus fluid is transported like a parcel on a conveyor belt. The use of alternating zeta potential fields and alternating electrode polarities allows to transport flow along multiple fields without the need to increase voltage. Basic functionality of the chip is accomplished by appropriate programming: fluid transport along straight and curved path, merging and splitting flow paths, flow crossing by red light traffic control, and mixing. Implementing sensors for electric resistance on the Lab-On-A-Chip allows to program a diagnosis application using electrophoresis for detection. Transport within the Lab-On-A-Chip can be described by Stokes-flow subject to the boundary conditions given by asymptotic theory in the thin-Debay-layer-limit describing field driven electro kinetic effects. [Preview Abstract] |
Tuesday, November 25, 2014 8:39AM - 8:52AM |
M10.00004: Transport Mechanisms of Circulating Tumor Cells in Microfluidic Devices Kaushik Rangharajan, A.T. Conlisk, Shaurya Prakash Lab-on-a-chip (LoC) devices are becoming an essential tool for several emerging point-of-care healthcare needs and applications. Among the plethora of challenging problems in the personalized healthcare domain, early detection of cancer continues to be a challenge. For instance, identification of most tumors occurs by the time the tumor comprises approximately 1 billion cells, with poor prognosis for metastatic disease. The key obstacle in identifying and subsequent capture of circulating tumor cells (CTCs) is that the amount of CTCs in the blood stream is $\sim$ 1 in 109 cells. The fundamental challenge in design and fabrication of microfluidic devices arises due to lack of information on suitable sorting needed for sample preparation before any labeling or capture scheme can be employed. Moreover, the ability to study these low concentration cells relies on knowledge of their physical and chemical properties, of which the physical properties are poorly understood. Also, nearly all existing microfluidic mixers were developed for aqueous electrolyte solutions to enhance mixing in traditional low Re flows. However, no systematic studies have developed design rules for particle mixing. Therefore, we present a numerical model to discuss design rules for microscale mixers and sorters for particle sorting for high efficiency antibody labeling of CTCs along with presenting a pathway for a device to capture CTCs without the need for labeling based on particle electrical properties. [Preview Abstract] |
Tuesday, November 25, 2014 8:52AM - 9:05AM |
M10.00005: Flow against the grain: a Newtonian microfluidic diode Jos\'e Alvarado, Jean Comtet, Anette Peko Hosoi Many biological structures are coated with a dense layer of fine hairs immersed in fluid, such as ciliary beds and microvilli brushes. These elastically deformable hairs are mechanically coupled to the fluid and can thus transduce mechanical forces. When hairs are slanted (forming a sub-normal angle to the surface) they deform differentially depending on whether fluid flows with or against the grain. Using theory and experiment, we show that a channel coated with slanted hairs leads to an anisotropic pressure drop. Surprisingly, this anisotropy holds for Newtonian fluids at arbitrarily low Reynolds numbers. We suggest that beds of slanted hairs could be used to build a Newtonian microfluidic diode. [Preview Abstract] |
Tuesday, November 25, 2014 9:05AM - 9:18AM |
M10.00006: Inertial instability of viscosity-stratified flows in microchannels Xiaoyi Hu, Thomas Cubaud The hydrodynamic stability of stratifications made between miscible fluids having large differences in viscosity is experimentally investigated in square microchannels. Parallel fluid layers with a fast central stream and a slow sheath flow are produced by focusing a low-viscosity fluid into a high-viscosity fluid in a straight microchannel. Although such fluid arrangements are typically governed with the flow rate ratio and the viscosity contrast at low Reynolds numbers Re, the formation of periodic wave trains at each fluid interface is observed for moderate Re. Several functional relationships are developed for the propagating velocity, size, and frequency of the generated waves over a range of viscosities and flow rates. In particular, we demonstrate the wave phase locking for small central streams and show the production of high-viscosity fluid ligaments at the wave crests. In this regime, minute amount of high-viscosity fluid is entrained and blended into the low-viscosity fluid recirculating plumes formed by the traveling interfacial waves. [Preview Abstract] |
Tuesday, November 25, 2014 9:18AM - 9:31AM |
M10.00007: Modeling and Simulation of Molecular Couette Flow in a Wide Range of Knudsen Number Li-Shi Luo, Wei Li, Zhaoli Guo, Jie Shen, Shidong Jiang We consider the planer Couette flow in a wide range of Knudsen number $0.003 \leq k \leq 10.0$. We first solve the integral equation derived from the linearized BGK equation. We then use the molecular dynamics (MD) to simulation the Couette flow with van der Waals interactions between channel walls and molecules. The kinetic solution and the MD are used to construct macroscopic model to simulation the flow. The macroscopic model is based on the lattice Boltzmann equation (LBE) with multiple-relaxation-time (MRT) model for collisions. The proposed MRT-LBE approach is shown to be effective and efficient to simulate molecular gaseous Couette flow in the entire range of Knudsen number. [Preview Abstract] |
Tuesday, November 25, 2014 9:31AM - 9:44AM |
M10.00008: Closing the gap: Exploring the limits of lubrication theory via molecular dynamics Amir M. Rahmani, Mehlam Jupiterwala, Yang Shao, Carlos E. Colosqui Advances in nanofabrication allow the engineering of nano-electromechanical systems and nanofluidic devices with dimensions on the order of 1 to 100 nanometers. Lubrication flows with characteristic lengths approaching the molecular scale have become ubiquitous in a wide spectrum of applications ranging from biomass sensing and atomic force microscopy to drug delivery and synthesis of nanomaterials. At nanometer scales, the effects of thermal fluctuations, disjoining pressure, and finite atomic size produce various phenomena beyond the reach of classical continuum hydrodynamics. We will present a theoretical and computational study on nanoscale lubrication flows where bodies immersed in dense fluid media either are kept under static conditions or are allowed to undergo thermal fluctuations about a prescribed position. We find that under static conditions, continuum-based lubrication models can accurately predict hydrodynamic forces computed via molecular dynamics simulations at surprisingly small scales (i.e., for flows having sub-nanometer-sized lubrication gaps). Thermal vibration, however, can induce drag reduction and other dynamic effects that can potentially be described by extending conventional lubrication models. [Preview Abstract] |
Tuesday, November 25, 2014 9:44AM - 9:57AM |
M10.00009: Flow rate and slip length measurements of water in single micrometer pipes Peter Taborek, Anerudh Kannan, David Mallin, Angel Velasco Measurements of pressure driven water flows in hydrophobic and hydrophilic fused quartz capillaries of 1.8 um diameter are compared. Typical flow rates of 1 picoliter/s and pressure drops up to 25 Atm were used. Water exited the capillaries into an oil reservoir where the volume of the pendant drop could be monitored using time lapse photography. The typical growth rate for the drop diameter was $\sim$ 300 $\mu$m per day. The drop size saturates due to diffusion at the interface. For the untreated quartz capillary the results are consistent with a slip of zero. The hydrophilic capillaries are chemically treated with octadecyltrichlorosilane (OTS) to form hydrophobic surfaces. Successful surface preparation is confirmed with the absence of capillary rise. Our technique can detect slip lengths above 20 nm. [Preview Abstract] |
Tuesday, November 25, 2014 9:57AM - 10:10AM |
M10.00010: Particle orientation during thermophoretic transport in a gas phase Steffen Hardt, Tobias Baier, Samir Shrestha, Sudarshan Tiwari, Axel Klar Using numerical and (semi)analytical techniques it is shown that during thermophoretic transport in a gas small particles may take a preferred orientation. For that purpose spherical model particles are considered, consisting of two hemispheres with diffuse and specular reflection boundary conditions, respectively. A Monte-Carlo method is used to simulate the translational and rotational dynamics of a particle colliding with surrounding gas molecules. The simulations show that a particle exposed to a temperature gradient takes a preferred orientation, moving through the gas with its diffusely reflecting hemisphere pointing towards the direction where the temperature is lower. In addition to that, in the free molecular flow regime the Langevin equation is used to study the rotational dynamics. In this regime it is possible to derive analytical expressions for the torque acting on the particle and for the dissipation force related to rotational motion. The stationary solution of the Langevin equation gives the probability density function for the particle orientation. The results could be of relevance for a number of processes in which nanoparticles are synthesized in a gas phase and deposited on a cold surface. [Preview Abstract] |
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