Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session Q07: Microscale Flows: General |
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Chair: Ali Mani, Stanford University Room: Georgia World Congress Center B212 |
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Tuesday, November 20, 2018 12:50PM - 1:03PM |
Q07.00001: Optimization of electroconvection over patterned membranes Jessie Liu, Ali Mani |
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Tuesday, November 20, 2018 1:03PM - 1:16PM |
Q07.00002: Abstract Withdrawn In conventional fluid dynamics, material-dependent properties of a fluid-solid interface are not considered when defining velocity boundary conditions, and simulations are thus not able to predict different outputs when chemical species at fluid-solid interfaces are varied. Assignment of material-dependent boundary conditions to macroscopic flows can be attained with the help of molecular dynamics. This multi-scale approach provides a systematic tool for the development of new materials with desired functional properties. In our ongoing research, we seek material-specific friction laws, relating shear rate and flow velocity at a given interface, by simulating a microscopic Couette flow. These laws can then be implemented as Neumann boundary conditions in a macroscopic flow. As part of a reliable protocol for translating microscopically determined properties into macroscopic boundary conditions, confinement effects must be filtered out. In this work, we investigate how the surface separation of the planar Couette setup affects important flow properties, such as shear rate, slip length, viscosity, temperature, and density. |
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(Author Not Attending)
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Q07.00003: An Acousto–Gravitational Balance in Climbing Films of liquid Ofer Manor, Amihai Horesh, Daniel Khaikin, Anna Zigelman A balance between acoustical, capillary, and gravitational stresses determines the extent in which a liquid film may climb over a vertical substrate, when it is excited by a MHz-frequency acoustic wave. Moreover, the rise level of the film against gravity serves as a simple tool for the measurement of the acoustic forcing in the film. The experimental system is made from a 20 MHz SAW (surface acoustic wave) actuator. The actuator is mounted on a vertical stage, so that its edge comes in contact with a reservoir of liquid. Partially wetting films of water and surfactant solutions, which satisfy finite three phase contact angles between the liquid, vapor, and the solid substrate, appear to reach a steady state height above the level of liquid in the reservoir. The theory predicts that the steady state height is a product of the balance between acoustical, capillary, and gravitational stresses in the film. In contrast, fully wetting films of oil are found to continuously wet and climb over the SAW device, ignoring gravity. The theory shows that the acoustical stress balances gravitational stress in the nearly flat oil film. The balance stabilises the thickness of the oil film, supporting its continuous rise. |
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Tuesday, November 20, 2018 1:29PM - 1:42PM |
Q07.00004: Ordered collective motion of magnetic swimmers Amir Nourhani, Vincent Crespi, Paul Lammert We study collective dynamics of systems of active colloids with an experimentally-realizable type of magnetically-induced long-range orientational interaction which can be aligning or anti-aligning. The phase diagram is mapped out as a function of interaction strength and density, showing various regimes of dynamically-stabilized orientational and positional order. |
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Tuesday, November 20, 2018 1:42PM - 1:55PM |
Q07.00005: Mass Transport across Two-Dimensional Graphene Nanopores Chengzhen Sun, Xiangyang Liu, Bofeng Bai Mass transport across two-dimensional nanopores is very essential to the porous graphene and other atomically thin membranes for gas separation. Due to the contribution of gas adsorption and diffusion over the two-dimensional surfaces, mass transport across two-dimensional nanopores cannot be described only by the kinetic theory of gases. We identify the molecular transport routes through two-dimensional nanopores and propose two permeation mechanisms (direct versus surface) with establishing their theoretical descriptions. The contribution of surface mechanism is especially analyzed by considering the surface adsorption and diffusion. The combination of the linear pressure-dependent direct flux, governed by the kinetic motion of gas molecules, and the nonlinear pressure-dependent surface flux, caused by the Langmuir isothermal adsorption characteristics of gas molecules on the two-dimensional surfaces, results in an overall nonlinear pressure dependence of the gas permeation flux through two-dimensional nanopores. We also reveal the mechanisms of the selective molecular permeation through nanopores, from the aspects of molecular size and structure, pore structure and the gas-graphene interactions. |
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Tuesday, November 20, 2018 1:55PM - 2:08PM |
Q07.00006: One dimensional theory of electrokinetic transport in deformable nanochannels Mpumelelo Matse, Peter Berg, Michael Eikerling In this work, we present a theoretical study of nonlinear coupling between wall deformation and water and ion flows in a charged, deformable nanochannel. The classical treatment of the mass and momentum conservation of the solid-liquid coupled system is based on the Stokes-Poisson–Nernst–Planck equations. For elastic but non-viscous walls undergoing small deformation, analytically solvable diferential equations were obtained in one dimension. Quantitative response of the walls’ relaxation dynamics and the channel’s electrokinetic transport was investigated at different charging regimes. Within the framework of nonequilibrium thermodynamics, compact formulae in terms of Onsager's phenomenological coefficients were derived for the electrokinetic transport parameters and energy conversion efficiency. Furthermore, an extension of the model is presented for electroactuator modelling which operates through a coupling of electrical and mechanical interactions for closed nanochannels. Numerical methods and results are presented, highlighting the significance of the fluid and charge redistribution on elastic deformations of the nanochannel. |
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Tuesday, November 20, 2018 2:08PM - 2:21PM |
Q07.00007: A complex droplet-based microfluidic platform for rapid immobilization of oligonucleotides on semiconductor quantum dots Hoang Anh Thu Nguyen, Abootaleb Sedighi, Ulrich Krull, Carolyn L. Ren Quantum dot-oligonucleotide DNA (QD-DNA) has attracted significant interest due to its applications in analytical chemistry. A current solid phase method to achieve immobilization of oligonucleotides DNA onto QDs involves a two-step reaction and be performed in a batch-based setting. Lately, droplet microfluidics, as a capable tool, offers numerous advantages that are unavailable for batch processing. Herein, we introduce a platform for rapidly immobilizing DNA onto QDs. The reagents used in batches are now divided into separated aqueous droplets, carried by oil phase. Notably, the device encapsulates QDs and magnetic beads (MB) in droplets for the QD-MB conjugates as the first step of the reaction. The second step is to merge other droplets containing DNA with these droplets in a merger. The merged droplets are pumped through a serpentine micro-channel for better mixing, resulting in the QD-DNA conjugation. This platform presents several benefits such as a higher degree of control of the reaction conditions; exclusion of the external vortexing and pipetting; minimized cross-contamination and impurities; plus, reduced cost due to the less reagent consumption. To evaluate the conjugation, we perform the fluorescence transduction of nucleic acid hybridization off-chip. |
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Tuesday, November 20, 2018 2:21PM - 2:34PM |
Q07.00008: Investigation of the crosstalk between multiple resonators in a single chip for simultaneous heating and sensing in microfluidics system Weijia Cui, Carolyn L. Ren In microfluidics system, microwave heating and sensing have been individually achieved for many applications. Simultaneous heating and sensing offers tremendous potential for tailored reaction which is high demand in material synthesis, however, it has always been very challenging. To fully realize the potential of simultaneous sensing and heating, at least two resonators with one sensing the droplet and the other heating it are needed. More resonators often provide more control and potential high throughput through multiplexing operation. But the crosstalk between resonators would limit the number of resonators. As the crosstalk usually results in the unwanted capacitive, inductive, and conductive coupling, which is the significant challenge for multiplexing performance. This study investigates the fundamental challenges of integrating two or more microwave resonators within a typical microfluidic device footprint. In order to prevent crosstalk, numerical simulation is carried out to investigate the limitation of the distance between two adjacent resonators. The ANSYS HFSS is used to perform the electromagnetic analysis based on the finite element method. Experimental studies are also conducted to validate the numerical results using vector network analyzer. |
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Tuesday, November 20, 2018 2:34PM - 2:47PM |
Q07.00009: Time-Resolved Temperature Field Measurement of Direct Contact Condensation of Steam in Subcooled Water using Backlight Aided Planar Laser Induced Fluorescence with High-speed Camera Se Ro Yang, Yassin A Hassan Instantaneous temperature field of vertical upward direct contact condensation of steam in subcooled water pool at the unstable bubbling condensation oscillation regime was measured using backlight aided planar laser induced fluorescence (PLIF) with high-speed camera. Rhodamine-B was used as fluorescence dye, and 532 nm wavelength laser sheet was applied to the test section to excite the fluorescent material. In-situ calibration was performed to obtain the spatially resolved correlation between the emission light intensity and temperature throughout the region of interest. Using the intensity-temperature correlation, temperature field around a site of the steam condensation was evaluated with the 2000 fps high-speed camera images. Results showed various instantaneous temperature field characteristics while phase change was occurring. Time-averaged temperature field showed the distinctive pattern of the average temperature gradient on both the single-phase and condensation regions. The detailed temperature field results obtained from this study can be extended to further investigation on the thermal-hydraulic bubble dynamics models for the specific condensation process. |
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