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 S35: Microscale Flows: Devices |
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Chair: Ivan Christov, Purdue University Room: 617 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S35.00001: Hydrostatic and hydrodynamic bulge testing of pre-stressed thick elastic plates for microfluidic applications Vishal Anand, Ivan C. Christov Bulge tests are used to characterize material properties of elastic sheets. We present a theory of hydrodynamic bulge tests based on the fluid--structure interaction between a deformable top wall of a rectangular microchannel and a viscous Newtonian fluid flow within. Taking into account uniform isotropic pre-stress within the wall, we derive a model for the deformation using first-order shear-deformation theory for thick plates. It is shown that pre-stress reduces the transverse deformation. Then, the mechanics problem is coupled to flow under the lubrication approximation, in a perturbative manner, to capture both the effect of (non-constant) hydrodynamic pressure on the deformation and the effect of wall deformation on the channel's hydrodynamic resistance. We obtain an analytical expression for the flow rate--pressure drop relation and show how it can be used to characterize the material properties (e.g., Young's modulus or pre-tension) of an elastic sheet without measuring its deformation, which is difficult to do accurately at the microscale. Direct numerical simulations are performed using the commercial software ANSYS to explore the range of validity of the proposed bulge testing theory. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S35.00002: Theory of the bulging effect of soft microchannels with thick walls Xiaojia Wang, Ivan C. Christov Long and shallow microchannels embedded in thick soft materials have been widely used in microfluidic devices. However, the bulging effect due to the fluid--structure interactions between the internal viscous flow and the soft walls has not been thoroughly understood. Previous models either contained a fitting parameter or were specialized to channels with thin walls. We present a theoretical study of the steady-state response of a deformable microchannel with a thick wall. Using lubrication theory for low-Reynolds-number flows and the linear elastic theory for isotropic solids, we obtain perturbative solutions for the flow and deformation. Specifically, only the channel's top wall deformation is considered, and its thickness-to-width ratio is assumed to be $(t/w)^2 \gg 1$. Then, we show that the deformation at each stream-wise cross-section can be considered independently, and that the top wall can be regarded as a simply supported rectangle subject to uniform transverse pressure at its bottom. The stress and displacement fields are found using Fourier series. Then, the channel shape and the hydrodynamic resistance are calculated, yielding a new flow rate--pressure drop relation without any fitting parameters. Our results agree favorably with previously reported experiments. [Preview Abstract] |
(Author Not Attending)
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S35.00003: Lego-fluidics: Building blocks for spatio-temporal microenvironment controller Bowen Ling, Ilenia Battiato Achieving a desired solute concentration distribution in micro-environments is vital to many applications, e.g. cell stimulation, single-molecule monitoring, micro-scale mixing and solid-free gel-casting. Controlled spatio-temporal solute distribution may be needed, e.g., to enhance mixing and reactions or to enforce a prescribed temporally varying signal during cell growth. This is currently achieved by active and passive methods. Active microfluidic mechanisms create varying concentration fields by changing the flow, while passive mechanisms are based on micropatterns ~which generate specific concentration ~signals due to their unique topology. ~Here, we propose a new design to generate target spatiotemporal solute distributions while minimizing perturbation to the flow field. The design, based on a valve system, provides greater versatility and flexibility than previous designs. We modulized all the controllers and provide examples of connection patterns in serial and parallel. [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S35.00004: Flow manipulation via the effects of shape geometry and topology Tejaswin Parthasarathy, Yashraj Bhosale, Fan Kiat Chan, Mattia Gazzola We demonstrate the importance of body curvature effects in achieving controlled flow manipulation in streaming settings. Here, we focus on microfluidic applications for inertial particle transport and mixing. We then challenge our understanding to explain prior experimental observations in two-dimensional flows. We further extend our exploration to three-dimensional flows where strategies related to body topology become accessible. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S35.00005: Regularized Inverse Holographic Volume Reconstruction for 3D flow diagnostics Jiarong Hong, Mallery Kevin We introduce regularized inverse holographic volume reconstruction (RIHVR) for 3D flow diagnostics using a single camera digital inline holographic particle tracking velocimetry (DIH-PTV). RIHVR solves an inverse problem whereby the 3D optical field best matching the recorded hologram is iteratively reconstructed utilizing the sparsity and spatial smoothness of the volume to regularize the solution. The reconstruction in RIHVR is substantially noise-free with improved axial resolution and increased maximum tracer concentration relative to prior DIH-PTV methods. The use of sparsity regularization in RIHVR enables a sparse data representation which reduces memory requirements and allows processing very large holographic images while simplifying the identification and tracking of individual particles. Using synthetic data, RIHVR shows a 40{\%} improvement in localization accuracy and a 4x reduction in the RMS velocity fluctuation in addition to a threefold increase in the allowable tracer concentration. RIHVR further demonstrates its capability through measurements of microfiber dynamics with nanometer resolution in all three directions, swimming tracks of algae in a dense suspension, and the rotation rate of non-spherical particles in a T-junction flow. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S35.00006: Understanding the Flow Mechanism in Micro Pulsating Heat Pipes Using Image Recognition Chihiro Kamijima, Yuta Yoshimoto, Shu Takagi, Ikuya Kinefuchi Heat generation in electronic devices has recently become a significant issue owing to their miniaturization and integration. Pulsating heat pipes (PHPs), which facilitate heat transfer via self-oscillation of liquid slugs, are promising devices thanks to their simple wickless structure and ease of miniaturization. However, complex and chaotic flow mechanism of PHPs has yet to be understood sufficiently, necessitating further investigation for device optimization. In this study, we fabricate a micro-PHP with a hydraulic diameter of 350 $\mu$m, and measure the PHP thermal conductivities using FC-72 as a working fluid under various conditions. We also visualize inner flows with a high speed camera and extract flow patterns using an image recognition technique. The results show that long and thin liquid films generated on the channel walls are of importance for effective heat transfer. Additionally, we model inner flows and heat transfer of the micro-PHP, and conduct numerical analyses using the extracted flow patterns. We find that latent heat transfer via the liquid films accounts for a significant portion of the overall heat transfer, while sensible heat transfer by the liquid slugs is negligible small. [Preview Abstract] |
Tuesday, November 26, 2019 11:49AM - 12:02PM |
S35.00007: Experimental and numerical analysis of the reaction yield in a T-microreactor Alessandro Mariotti, Chiara Galletti, Elisabetta Brunazzi, Roberto Mauri, Maria Vittoria Salvetti Microfluidic devices are attracting considerable interest in pharmaceutical and fine chemistry industry, because they allow continuous reactions with an unprecedented control over operating conditions. One critical issue in the use of microreactors is to obtain an efficient mixing and a high reaction yield while the flow being laminar, due to the small dimensions. In this context, the simplest and most studied configuration is the T-shaped one. The flow regimes occurring in these devices as the Reynolds number varies and the related mixing are well characterized in the literature. On the other hand, there is a little understanding of the effect of flow regimes on the yield of a chemical reaction. The present work is aimed at analyzing this aspect through the synergic use of experiments and numerical simulations. PIV measurements are used to characterize the flow pattern and optical techniques are employed to measure the reaction yield because the test-reaction is accompanied by discoloration. Simulations are based on finite-volume technique and local grid-adaptation. The chosen test-reaction is catalyzed by an acid in a homogeneous phase and this allow to easily investigate the combined effect of the Damköhler and of the Reynolds numbers on the reaction yield. [Preview Abstract] |
Tuesday, November 26, 2019 12:02PM - 12:15PM |
S35.00008: A PDMS based passive microfluidic device for generating Platelet rich plasma Vijai Laxmi, Siddhartha Tripathi, Suhas S Joshi, Amit Agrawal Platelets are a pool of various growth factors which act as a soft tissue healer, and are also linked to various pathophysiological diseases. Platelet rich plasma (PRP) finds wide applications in platelet transfusion and biomedical research. Therefore, there is merit in selectively extracting platelets from blood. Clinically, platelets rich plasma is separated based on centrifugation process, which is however time consuming and leads to activation of platelets. The existing microdevices suffer from low throughput and have been tested only with dilute blood. Here, we design and test a passive PDMS based microdevice for obtaining PRP from whole human blood. The features involved in the microdevice are simple, and its fabrication involves a single layer of photolithography. The microdevice utilizes hydrodynamic forces for its operation, which are based on the biophysical laws and geometrical effects. The microdevice separates plasma with 14 - fold enrichment of platelets in it, while working in 0.2 ml/min to 0.4 ml/min flow rate range. The quality of the outlet sample is also checked by measuring the activation level of platelets, less than 5{\%} platelets are found to be activated. These features make the presented microdevice unique. [Preview Abstract] |
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