Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session G35: Microscale Flows: General |
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Chair: Bud Homsy, University of Washington Room: 617 |
Sunday, November 24, 2019 3:48PM - 4:01PM |
G35.00001: Taylor dispersion in the presence of cross flow and interfacial mass transfer Tiras Y. Lin, Eric S.G. Shaqfeh Transverse velocity gradients can enhance the effective diffusion coefficient of a scalar in the primary flow direction — a phenomenon known colloquially as Taylor dispersion. In this work, we perform Taylor dispersion analysis on a pressure-driven flow in a channel with a cross flow, using both perturbation theory and Brownian dynamics simulations. Moreover, we illustrate how mass transfer at the wall affects the evolution of the scalar. We elucidate how the effective diffusion coefficients, effective advective velocities, and effective mass-transfer rates depend on the strength of the cross flow and the wall transfer coefficient, and we perform an asymptotic analysis to investigate the limit of strong cross flow. We discuss a few applications where our results may be useful. For example, in the treatment of a cancerous tumor using nanoparticles, interactions with red blood cells drive nanoparticles in the transverse direction toward the porous blood vessel wall, where they can then be transferred through the wall. Additionally, it has recently been shown that applied forces can cause particles to drift laterally in a viscoelastic channel flow. In both of these applications, our results can be used to understand the resulting particle dispersion. [Preview Abstract] |
Sunday, November 24, 2019 4:01PM - 4:14PM |
G35.00002: Dispersion control in deformable microchannels Garam Lee, Abigail Taylor, Alan Luner, Jeremy Marzuola, Daniel Harris In fully-developed pressure-driven flow, the spreading of a dissolved solute is enhanced in the flow direction due to transverse velocity variations in a phenomenon now commonly referred to as Taylor dispersion. It is well understood that the characteristics of the dispersion are sensitive to the channel's cross-sectional geometry. Here we demonstrate a method for manipulation of dispersion properties in a single microchannel via controlled deformation of one of the channel's walls. Using a rapid-prototyped multi-layer microchip, the upper channel wall is deformed by an external pressure source allowing us to characterize the dependence of the dispersion on the deflection of the channel wall and overall channel aspect ratio. Our experimental measurements are compared directly with theoretical predictions. [Preview Abstract] |
Sunday, November 24, 2019 4:14PM - 4:27PM |
G35.00003: Identification and decomposition of advective transfer on micro-textured surfaces Yanxing Wang, Tie Wei Through well-designed physical models and high-fidelity numerical simulations, the physics of advective heat and mass transfer on a solid surface embedded with structured micro pillars is revealed. Two types of advection mechanism are identified, local advection and long-range advection, corresponding to the eddy recirculation in the gaps between streamwise neighboring pillars and the fluid circulation between the regimes above and below pillar tips. The flow topologies suggest that the flow of local advection recirculates primarily in \textit{xz} plane, and the flow of long-range advection recirculates in \textit{yz} plane. This fact allows for the decomposition of the two mechanisms by averaging the flow quantities in the streamwise and spanwise coordinates. The enhancement of heat and mass transfer by local and long-range advection is examined for typical geometries, and the transition of the primary transfer method between the two mechanisms due to geometrical change is analyzed in detail. The dependence of local and long-range advection on streamwise and spanwise distances between micro pillars is identified, and this offers promising potential for the accurate control of heat and mass flux in micro fluidics. [Preview Abstract] |
Sunday, November 24, 2019 4:27PM - 4:40PM |
G35.00004: A Quantitative Study of the Effect of Flow on the Photopolymerization of Fibers Malcolm Slutzky, Howard Stone, Janine Nunes The gelation resulting from the interaction between a continuously flowing photo-crosslinkable fluid and pulsed-UV light can be used to produce uniform flexible microfibers. We study this process of fiber production by investigating the conditions required for gelation and by developing a steady-state flow model of the gelation process, which captures the effects of UV exposure on the spatial concentration of radical species and molecular oxygen in the direction of flow. Using this model, we are able to predict critical conditions for fiber production and verify these predictions with our experimentally-observed results. Additionally, we define three regimes of fiber production (in which no fibers, non-uniform fibers, and uniform fibers are produced), qualitatively characterize relationships between fiber length and rigidity, and, with insight drawn from the mathematical model, develop guidelines for the standardized production of uniform fibers with predictable and controllable length. [Preview Abstract] |
Sunday, November 24, 2019 4:40PM - 4:53PM |
G35.00005: Measurement of pressure field in microchannel flow from velocity data obtained from micro-PIV Shingo Ota, Ken Yamamoto, Masahiro Motosuke Dynamics inside and outside of cells and bubbles/droplets in microchannels, $e.g.$, mechanical characteristics of cells and interfacial behavior in multiphase flows, are complicated and difficult to be reproduced by the numerical simulation. To understand these phenomena, a measurement technique that can obtain precise pressure fields of liquid is required. A pressure-field calculation from velocity fields is one possible scenario to obtain the pressure field in microscopic domain where inserting pressure probes is hardly achieved. The present study investigates a reconstruction of pressure fields from velocity fields obtained by micro-PIV based on the Navier-Stokes equation. Fast Fourier transformation (FFT) is used in the pressure-field calculation. And the pressure fields calculated from micro-PIV are compared with CFD results. By preparing artificial particle images with different image resolution, we investigate effects of the image resolution and errors due to the PIV analysis on the accuracy of the pressure-field calculation. As a result, it is shown that the method can reproduce the pressure fields despite the fact that the velocity data contains error. Moreover, the accuracy of both the velocity and the pressure fields can be improved as the increase of the resolution of the artificial particle images. [Preview Abstract] |
Sunday, November 24, 2019 4:53PM - 5:06PM |
G35.00006: Gas-assisted Taylor Cone-Jets Francisco Cruz-Mazo, Max O. Wiedorn, Miguel A. Herrada, Gisel E. Pena-Murillo, Juraj Knoska, Sasa Bajt, Henry N. Chapman, Alfonso M. Ganan-Calvo We introduce a way to produce steady micro/nano-liquid jets via electric fields together with co-flowing gas streams. We study the dripping-jetting transition of this configuration theoretically through a global stability analysis as a function of the governing parameters involved. Indeed, we derive two coupled scaling laws that predict both the minimum jet diameter and its maximum velocity. The theoretical prediction provides a single curve that describes not only the numerical computations but also experimental data from the literature for cone-jets. Additionally, we performed a set of experiments to verify what parameters influence the jet length. Due to the diameters below 1 micrometer and high speeds attainable in excess of 100 m/s, this concept has the potential to be utilized for structural biology analyses with X-ray free-electron lasers at megahertz repetition rates as well as other applications. [Preview Abstract] |
Sunday, November 24, 2019 5:06PM - 5:19PM |
G35.00007: An Elastic filament in a time-periodic linear shear flow Vipin Agrawal, Dhrdubaditya Mitra We numerically study the dynamics of a free elastic filament in a highly viscous linear shear flow in the absence of inertia and brownian motion. We use a bead-spring model with Rotne-Pragor viscosity [1]. In time-independent shear flow the filament shows tumbling, C-buckling, and snake-turn, before becoming straight at late times [2,3,4], for different elasto-viscous numbers, $\Gamma$ -- Dimensionless ratio of viscous and elastic stress. In time-periodic flow (Period T), for $\Gamma < \Gamma_1$, as expected the filament comes back to it's initial position after one period. Surprisingly, for $\Gamma_1 < \Gamma < \Gamma_2$, we find two-cycle -- the filament comes back to it's initial shape not after one but two periods. For $\Gamma > \Gamma_2$, we observe complex dynamical behaviors. Our results are independent of choice of initial conditions. \\ (1) H. Wada and R. R. Netz, EPL (Europhysics Letters)75, 645 (2006). (2) L. E. Becker and M. J. Shelley, Physical Review Letters 87, 198301 (2001).\\ (3) L. Guglielmini, A. Kushwaha, E. S. Shaqfeh, and H. A. Stone, Physics of Fluids 24, 123601 (2012). \\ (4) Y. Liu, B. Chakrabarti, D. Saintillan, A. Lindner, and O. du Roure, Proceedings of the National Academy of Sciences 115, 9438 (2018). [Preview Abstract] |
Sunday, November 24, 2019 5:19PM - 5:32PM |
G35.00008: Flow physics of single-phase laminar flow through diamond microchannel Sandeep Goli, Sandip Kumar Saha, Amit Agrawal Diamond microchannel is a varying cross-section microchannel with diverging and converging flow passages. Flow in such devices has significance in the design of micromixers, micropumps and microreactors. Three-dimensional numerical analysis of single-phase laminar liquid flow has been performed to understand the effect of the given configuration on flow parameters such as pressure drop and Poiseuille number. The results show that pressure drop in given configuration are consistent with theoretical predictions, which suggests that existing correlations for uniform microchannels can be applied to the present configuration. Towards this, an appropriate length scale has been identified to make the hydrodynamic flow resistance of the diamond microchannel is same as that of an equivalent uniform microchannel. This is located at 1/7th of the total length of the microchannel from its inlet. This location makes the hydrodynamic resistance of microchannel independent of its geometric and flow parameters. In addition, flow physics has been studied with the help of velocity, pressure and shear stress profiles. [Preview Abstract] |
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