Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session F14: Microscale Flows: ParticlesMicro Particles
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Chair: Luca Cortelezzi, Politecnico di Milano Room: 507 |
Monday, November 20, 2017 8:00AM - 8:13AM |
F14.00001: Miniaturized inertial impactor for personal airborne particulate monitoring: Numerical model Luca Cortelezzi, Silvia Pasini, Elena Bianchi, Gabriele Dubini The rising level of fine particle matter's (PM$_{10}$, PM$_{2.5}$ and PM$_{1}$) pollution in the world has increased the interest in developing portable personal air-qualitity monitoring systems. To answer this need, we conceived a miniaturized inertial impactor. The development of such an impactor becomes more challenging as the diameter of the particles to be collected becomes smaller, since the velocities required to induce the impact of finer particulate matter become higher. To overcome these challenges, we modeled numerically the fluid dynamics and particles transport within the impactor. Our simulations show that the fluid flow within the impactor becomes unstable as the Reynolds number is increased to capture finer particles. Furthermore, the onset of these instabilities depends not only on the Reynolds number but also on the geometry of the impactor. The unsteady flow within the impactor influences the trajectories of the particles to be collected, especially the smaller particles. The particles trajectories shows that the impaction location varies substantially as the Reynolds number increases and, consequently, the efficiency of the impactor deteriorates. Finally, we optimize the design of our impactor to maximize its collection efficiency. [Preview Abstract] |
Monday, November 20, 2017 8:13AM - 8:26AM |
F14.00002: Miniaturized inertial impactor for personal airborne particulate monitoring: Prototyping Silvia Pasini, Elena Bianchi, Gabriele Dubini, Luca Cortelezzi Computational fluid dynamic (CFD) simulations allowed us to conceive and design a miniaturized inertial impactor able to collect fine airborne particulate matter (PM$_{10}$, PM$_{2.5}$ and PM$_{1}$). We created, by 3D printing, a prototype of the impactor. We first performed a set of experiments by applying a suction pump to the outlets and sampling the airborne particulate of our laboratory. The analysis of the slide showed a collection of a large number of particles, spanning a wide range of sizes, organized in a narrow band located below the exit of the nozzle. In order to show that our miniaturized inertial impactor can be truly used as a personal air-quality monitor, we performed a second set of experiments where the suction needed to produce the airflow through the impactor is generated by a human being inhaling through the outlets of the prototype. To guarantee a number of particles sufficient to perform a quantitative characterization, we collected particles performing ten consecutive deep inhalations. Finally, the potentiality for realistic applications of our miniaturized inertial impactor used in combination with a miniaturized single-particle detector will be discussed. [Preview Abstract] |
Monday, November 20, 2017 8:26AM - 8:39AM |
F14.00003: Large Scale Brownian Dynamics of Confined Suspensions of Rigid Particles Aleksandar Donev, Brennan Sprinkle, Florencio Balboa, Neelesh Patankar We introduce new numerical methods for simulating the dynamics of passive and active Brownian colloidal suspensions of particles of arbitrary shape sedimented near a bottom wall. The methods also apply for periodic (bulk) suspensions. Our methods scale linearly in the number of particles, and enable previously unprecedented simulations of tens to hundreds of thousands of particles. We demonstrate the accuracy and efficiency of our methods on a suspension of boomerang-shaped colloids. We also model recent experiments on active dynamics of uniform suspensions of spherical microrollers. [Preview Abstract] |
Monday, November 20, 2017 8:39AM - 8:52AM |
F14.00004: Inertial Migration and Focusing of particles in a Porous Microchannel Mike Garcia, Sumita Pennathur The behavior of confined particles at high Reynolds number allows for potential advances in separation and concentration of particles. Although researchers can differentiate the location of inertially focused particles based on their size, the variability in size amongst bioparticles is often a limiting factor for viable applications. In this work, we numerically investigate a method to actively tune the focusing location of particles and thereby overcome this limitation. We show that a transverse flow due to a porous wall in a straight microchannel can precisely tune the equilibrium location of particles. For channel Reynolds number below 200, our studies show that the focusing location of spherical particles is described by a single parameter $i.e.$, the ratio between transverse drag and inertial lift forces. At positive values of this parameter, the equilibrium is found near the wall whereas the equilibrium is found near the centerline for negative values. Additionally, we demonstrate that under certain conditions the state of the equilibrium location (stable vs. unstable) can change at a critical value of this parameter. The insight gained through this study can be applied in the design of novel separation techniques, where \textit{in situ} manipulations of particles are needed. [Preview Abstract] |
Monday, November 20, 2017 8:52AM - 9:05AM |
F14.00005: Abstract Withdrawn
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Monday, November 20, 2017 9:05AM - 9:18AM |
F14.00006: Inertial Particle Focusing Regimes in Suspension Flows through Square Dusts Hiroshi Yamashita, Tomoaki Itano, Masako Sugihara-Seki Particles suspended in laminar flows through rectangular ducts are known to cross streamlines towards a discrete set of equilibrium positions in the duct cross section, due to the lateral force exerted on the particles arising from the inertial effect. For square duct flows, in particular, suspended particles were observed to be focused on four points at the center of channel faces at low Reynolds numbers. In the case of larger particle-to-duct-size ratios ($\ge$ 0.3), however, a numerical study predicted that this type of equilibrium positions becomes unstable at similar Reynolds numbers and another type of equilibrium positions located on the diagonal near the channel corners becomes stable. In addition to these two types of equilibrium positions, recent experimental and numerical studies showed the presence of a new type of equilibrium positions on the heteroclinic orbit joining the above two types of equilibrium positions for the size ratio $\sim$ 0.1. In this study, we investigated experimentally and numerically the equilibrium positions of neutrally buoyant spherical particles in square duct flows and classified their focusing regimes according to their stability, for the size ratio between 0.1 and 0.3 in a wide range of Reynolds numbers. [Preview Abstract] |
Monday, November 20, 2017 9:18AM - 9:31AM |
F14.00007: Symmetric pair of elongated particles settling at low Reynolds number regime Marek Bukowicki, Maria Ekiel-Jezewska Numerical results for dynamics of rigid and semi-flexible filaments settling down at low Reynolds number regime will be presented. Particles are assumed to be large enough to not experience significant influence of Brownian forces. For modelling, bead model and Rotne–Prager–Yamakawa approximation are used. Initial position of filaments is symmetric, with vertical symmetry plane. Due to this symmetry of the system, obtained results are valid also for a single particle, dragged by a force parallel to a plain surface of the fluid (by correspondence with method of images for forces near free surface). It was reported before that rigid filaments, placed initially in a vertical plane, tumble periodically. Here we generalize these results for all symmetric configurations and in this way extend known class of periodic solutions. When filaments are flexible, richer behaviour is found: initially particles oscillate, yet oscillations are dumped with time, leading to non-oscillating motion where filaments approach each other. [Preview Abstract] |
Monday, November 20, 2017 9:31AM - 9:44AM |
F14.00008: Acoustic-assisted fluidic hourglasses Tamara Guimaraes, Alvaro Marin, Christian J. Kaehler, Rune Barnkob Microfluidic devices are prone to get clogged when suspensions are forced through narrow passages. Such clogging events occur when particles form arches that block the channel. In this work we study the clogging probabilities in a microfluidic hourglass when subject to ultrasound. We measure the clogging probabilities for certain ranges of sound amplitudes and particle-to-neck size ratios in which clogging events are more likely to occur. The ultrasound induces acoustic radiation forces on the suspended particles, leading to particle migration perpendicular to the channel flow direction. The transverse particle rearrangement can significantly reduce the clogging probability by decreasing the chances of arching in the narrowing of the passage. We show that by choosing proper sound actuation conditions, the method is reliable, non-intrusive, preventive, and allows to increase the life of fluidic devices (microfluidic or larger) with particles in a wide range of sizes. [Preview Abstract] |
Monday, November 20, 2017 9:44AM - 9:57AM |
F14.00009: On the Motion of an Ellipsoid in a quadratic field Curtis P. Martin, Shiyan Wang, Sangtae Kim In this presentation, we show that the Stokes flow surface tractions on a force-free, torque-free ellipsoid in an ambient quadratic velocity field have a simple relationship to the boundary condition on the ellipsoid of the associated disturbance velocity fields. This is reminiscent of the corresponding results for the surface tractions of an ellipsoid in rigid body motion as articulated by Brenner (1964) and explained by Kim (2015) using the self-adjoint property of the double layer operator in the appropriate metric space. These results provide a basis for the exploration of the spectrum of the double layer operator for the ellipsoid, with a view towards the ultimate construction of the biorthogonal expansion of the double layer operator with eigenvalues and eigenfunctions ordered by the far field decays in inverse powers of the radial distance from the ellipsoid center. The orthonormal properties of eigenfunctions of a self-adjoint operator may then be exploited to provide a new and useful velocity representation for an ellipsoid in Stokes flow. [Preview Abstract] |
Monday, November 20, 2017 9:57AM - 10:10AM |
F14.00010: Isolation of nanoscale exosomes using viscoelastic effect. Guoqing Hu, Chao Liu Exosomes, molecular cargos secreted by almost all mammalian cells, are considered as promising biomarkers to identify many diseases including cancers. However, the small size of exosomes (30-200 nm) poses serious challenges on their isolation from the complex media containing a variety of extracellular vesicles (EVs) of different sizes, especially in small sample volumes. Here we develop a viscoelasticity-based microfluidic system to directly separate exosomes from cell culture media or serum in a continuous, size-dependent, and label-free manner. Using a small amount of biocompatible polymer as the additive into the media to control the viscoelastic forces exerted on EVs, we are able to achieve a high separation purity (\textgreater 90 {\%}) and recovery (\textgreater 80 {\%}) of exosomes. The size cutoff in viscoelasticity-based microfluidics can be easily controlled using different PEO concentrations. Based on this size-dependent viscoelastic separation strategy, we envision the handling of diverse nanoscale objects, such as gold nanoparticles, DNA origami structures, and quantum dots. [Preview Abstract] |
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