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 A14: Microscale Flows: DevicesMicro
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Chair: Sangjin Ryu, University of Nebraska-Lincoln Room: 507 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A14.00001: Experimental and numerical analyses of flow and mixing regimes in an arrow-like micro mixer Maria Vittoria Salvetti, Alessandro Mariotti, Chiara Galletti, Elisabetta Brunazzi T-mixers are among the most common micro devices. We focus here on a geometrical modification of a T-mixer obtained by varying the angle between the axis of the inlet channels and that of the main conduit, so that an 'arrow-like' configuration is obtained. Previous numerical studies indicated that for this type of configuration the steady engulfment regime occurs at lower Reynolds numbers than for T-mixers. However, with further increasing the Reynolds number, an unexpected reduction of the degree of mixing is observed, due to the presence of a strong vortical structure at the center of the mixing channel. Such a behavior is not observed in T- mixers. A synergic analysis combining experimental flow visualizations and numerical simulations of an arrow-like micro mixer is presented here. Experimental flow visualizations are compared with the scalar field behavior obtained in the simulations, which is in turn connected with the vorticity fields and dynamics, available in numerical simulations. This analysis is aimed at: (i) further characterizing the steady engulfment regime and (ii) investigating the unsteady periodic regimes, eventually occurring by increasing the Reynolds number, which have not been addressed so far in the literature for this type of geometry. [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A14.00002: Experimental and numerical analyses of flow and mixing regimes in a micro T-mixer Alessandro Mariotti, Chiara Galletti, Maria Vittoria Salvetti, Elisabetta Brunazzi Among the most common micro-devices, T-mixers, in which the inlets join the main channel with T-shaped branches, are widely used. Despite the very simple geometry, the laminar flow dynamics and mixing in a T-shaped micro-mixer are really complex. Different flow regimes have been identified and studied in the literature: by increasing the Reynolds number, steady regimes occur, namely the stratified, the steady symmetric (vortex), the steady asymmetric (engulfment) and then unsteady periodic regimes, namely the periodic asymmetric, the periodic symmetric, and finally the chaotic regime. These regimes have been characterized in details by using numerical simulations and flow stability analyses. Experimental studies are more limited, especially as far as unsteady regimes are concerned. A synergic analysis combining experimental flow visualizations and numerical simulations is presented here. A very good agreement is obtained between passive scalar concentration in numerical simulations and experimental flow visualizations. The scalar field behavior is connected with the vorticity dynamics available in numerical simulations. For the unsteady regimes, experimental characterization of the flow features suggested by previous numerical studies is shown for the first time. [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A14.00003: An Experimental Study of Vortex Flow Formation and Dynamics in Confined Microcavities Reem Khojah, Dino Di Carlo New engineering solutions for bioparticle separation invites revisiting classic fluid dynamics problems. Previous studies investigated cavity vortical flow that occurs in 2D with the formation of a material flux boundary or separatrix between the main flow and cavity flow. We demonstrate the concept of separatrix breakdown, in which the cavity flow becomes connected to the main flow, occurs as the cavity is confined in 3D, and is implicated in particle capture and rapid mass exchange in cavities. Understanding the convective flux between the channel and a side cavity provides insight into size-dependent particle capture and release from the cavity flow. The process of vortex formation and separatrix breakdown between the main channel to the side cavity is Reynolds number dependent and can be described by dissecting the flow streamlines from the main channel that enter and spiral out of the cavity. Laminar streamlines from incremented initial locations in the main flow are observed inside the cavity under different flow conditions. Experimentally, we provide the Reynolds number threshold to generate certain flow geometry. We found the optimal flow conditions that enable rapid convective transfer through the cavity flow and exposure and interaction between soluble factors with captured cells. By tuning which fraction of the main flow has solute, we can create a dynamic gate between the cavity and channel flow that potentially serves as a time-dependent fluid exchange approach for objects within the cavity. [Preview Abstract] |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A14.00004: Controlling Flow Speed in Microfluidic Paper-based Analytical Devices via Hollow Channels Haipeng Zhang, Danielle Barmore, Sangjin Ryu Microfluidic paper-based analytical devices ($\mu $PADs) consist of hydrophilic paper patterned with hydrophobic barriers to create paper-based flow channels. Because a liquid sample is transported through the paper channel by capillary force, resultant flow speed is usually low, which is one limitation of conventional $\mu $PADs. In contrast, adding a hollow channel layer aligned with a paper channel can significantly increase the flow speed of a testing sample in $\mu $PADs. Liquid flow through the hollow channel appears to be driven by a pressure gradient while affected by surface wettability of the surrounding channel surfaces. It is also possible to control the flow speed by modifying the design of the hollow channel. In order to find underlying fluid dynamics principle, this study investigates the relationship between the flow speed through hollow channels in the $\mu $PAD and the design of the hollow channel. [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A14.00005: Microfluidic Bypass Manometry: Parallelized measurement of flow resistance of complex channel geometries and trapped droplets Siva Vanapalli, Naureen Suteria, Mehdi Nekouei We report a technique referred to as ``microfluidic bypass manometry'' for measurement of pressure drop versus flow rate ($\Delta $P-Q) relations in a parallelized manner. It involves introducing co-flowing laminar streams into a microfluidic network that contains a series of loops, where each loop contains a test geometry and a bypass channel as a flow rate sensing element. To demonstrate the technique, we measure $\Delta $P-Q relations simultaneously for forty test geometries ranging from linear to contraction-expansion to serpentine to pillar-laden microchannels. The measured Newtonian flow resistance of these different geometries is in excellent agreement with CFD simulations. To expand the capabilities of the method, we measured $\Delta $P-Q relations for similar-sized oil droplets trapped in microcavities where the cavity geometry spans from prisms of 3 -- 10 sides to cylinders. We find in all cases, $\Delta $P-Q relation is nonlinear and the flow resistance is sensitive to drop confinement and weakly dependent on cavity geometry. We anticipate that microfluidic bypass manometry may find broad application in several areas including design of lab-on-chip devices, laminar drag reduction, rheology of complex fluids and mechanics of deformable particles. [Preview Abstract] |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A14.00006: Simulations of the Flow in the Liquid Floating Micro-gyroscope Fei Tang, Chun Ze Wang, Qi Li, Xiao Hao Wang The interactions between the centrifugal force, the cavity and the scale effect make the flow become complicated when the rotor of liquid floating micro-gyroscope rotates in a confined space at a high speed. In this paper, The Reynolds averaged equations were solved with simulation and the distribution laws of the mean flow, turbulent statics and drag were obtained in different Reynolds numbers and aspect ratios of the cavity. The circumferential velocities along z direction changed from linearity to nonlinearity with the increasing of Reynolds number, corresponding to torsional Couette flow To Batchelor flow. The radial velocities kept S shape with different maximum value and the axial velocities were nearly zeros except very close to the inner and the outer cylinders. For Reynolds stresses, they were concentrated in the vicinity of the boundary layer and the normal stresses were slightly higher than shear stresses. The drag coefficients increased with the increasing of the Reynolds number. But the growth rates were not the same in different parameters. This paper provides a guidance for the manufacture of the liquid floating micro-gyroscope. [Preview Abstract] |
Sunday, November 19, 2017 9:18AM - 9:31AM |
A14.00007: Improved Fibrinolysis Using Magnetically Driven Colloidal Microwheels Dante Disharoon, Onur Tasci, Rogier Schoeman, Kuldeepsinh Rana, Paco Herson, David Marr, Keith Neeves At the microscale, fluid dynamics are unique because viscous forces dominate over inertial forces, with Reynolds numbers typically less than unity. To move through microscale channels (order 100 $\mu$ m) over macroscale distances (\textgreater 1 cm) devices based on cellular machinery have been developed, but they are slow and difficult to implement within in vivo environments. To address these issues, we report the assembly and translation of magnetically-powered colloidal microwheels ($\mu$ wheels) capable of translation at speeds of over 100 $\mu$ m/s. In this, superparamagnetic microparticles cluster into wheel-like shapes that spin when subject to an order milliTesla planar rotating magnetic field. By exploiting wet friction between $\mu$ wheels and adjacent surfaces, not only can significant $\mu$ wheel translation speeds be achieved but also travel direction can be precisely and rapidly controlled. With both assembly and translation manipulated via non-gradient external magnetic fields that do not attenuate in tissue, this method is well-suited for drug delivery. We demonstrate this by showing that $\mu$ wheels functionalized with fibrinolytics can dissolve blood clots five-fold faster than soluble fibrinolytics at therapeutic concentrations. [Preview Abstract] |
Sunday, November 19, 2017 9:31AM - 9:44AM |
A14.00008: Nature-inspired multifunctional membrane fabricated by adaptive hybridization of PNIPAm and PPy. Hyejeong Kim, Kiwoong Kim, Sang Joon Lee Specialized plant organs, such as guard cells of stomata, consist of soft materials with deformability and electrochemical properties in response to various environmental stimuli. Stimulus-responsive hydrogels with electrochemical properties are good candidates for imitating such functionalities having great potential in a wide range of applications. However, conductive hydrogels are usually mechanically rigid and the fabrication technology of structured hydrogels has low reproducibility. Here, inspired by stimulus-responsive functionalities of plants, a thermo-responsive multifunctional hybrid membrane (HM) is synthesized through the in situ hybridization of conductive poly(pyrrole)(PPy) on a photopolymerized poly(N-isopropylacrylamide)(PNIPAm) membrane. The various properties of the HM are investigated to characterize its multiple functions. In terms of morphology, the HM can be easily fabricated into various structures, and exhibits thermo-responsive deformability. In terms of functionality, it exhibits various electrical and charge responses to thermal stimuli. This simple and efficient fabrication method can be used as a promising platform for fabricating a variety of functional devices, such as actuators, biosensors, and filtration membranes. [Preview Abstract] |
Sunday, November 19, 2017 9:44AM - 9:57AM |
A14.00009: Smart cover glass for automotive applications Sang Kug Chung This paper presents a smart cover glass based on electrowetting-on-dielectric (EWOD) actuation for automotive applications. It can remove water droplets in a wide range of sizes to allow the camera's lens to get clean at any time. The proposed cover glass offers a simple design structure to be easily installed on any device but provides a fast and energy efficient droplet cleaning operation. As proof of concept, a real imaging test is carried out using a mobile smartphone camera and landscape photography. When water droplets with different volumes are on the camera cover glass, the image of landscape photography is distorted with blurred spots. However, the distorted image is restored by removing the droplets through EWOD actuation. [Preview Abstract] |
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