Journal articles: 'Mixing at Microscale'

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Ober, Thomas J., Daniele Foresti, and Jennifer A. Lewis. "Active mixing of complex fluids at the microscale." Proceedings of the National Academy of Sciences 112, no. 40 (September 22, 2015): 12293–98. http://dx.doi.org/10.1073/pnas.1509224112.

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Mixing of complex fluids at low Reynolds number is fundamental for a broad range of applications, including materials assembly, microfluidics, and biomedical devices. Of these materials, yield stress fluids (and gels) pose the most significant challenges, especially when they must be mixed in low volumes over short timescales. New scaling relationships between mixer dimensions and operating conditions are derived and experimentally verified to create a framework for designing active microfluidic mixers that can efficiently homogenize a wide range of complex fluids. Active mixing printheads are then designed and implemented for multimaterial 3D printing of viscoelastic inks with programmable control of local composition.

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Heyman, Joris, Daniel R. Lester, Régis Turuban, Yves Méheust, and Tanguy Le Borgne. "Stretching and folding sustain microscale chemical gradients in porous media." Proceedings of the National Academy of Sciences 117, no. 24 (May 28, 2020): 13359–65. http://dx.doi.org/10.1073/pnas.2002858117.

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Fluid flow in porous media drives the transport, mixing, and reaction of molecules, particles, and microorganisms across a wide spectrum of natural and industrial processes. Current macroscopic models that average pore-scale fluctuations into an effective dispersion coefficient have shown significant limitations in the prediction of many important chemical and biological processes. Yet, it is unclear how three-dimensional flow in porous structures govern the microscale chemical gradients controlling these processes. Here, we obtain high-resolution experimental images of microscale mixing patterns in three-dimensional porous media and uncover an unexpected and general mixing mechanism that strongly enhances concentration gradients at pore-scale. Our experiments reveal that systematic stretching and folding of fluid elements are produced in the pore space by grain contacts, through a mechanism that leads to efficient microscale chaotic mixing. These insights form the basis for a general kinematic model linking chaotic-mixing rates in the fluid phase to the generic structural properties of granular matter. The model successfully predicts the resulting enhancement of pore-scale chemical gradients, which appear to be orders of magnitude larger than predicted by dispersive approaches. These findings offer perspectives for predicting and controlling the vast diversity of reactive transport processes in natural and synthetic porous materials, beyond the current dispersion paradigm.

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Enfield, Kent, Jeremy Siekas, and Deborah Pence. "LAMINATE MIXING IN MICROSCALE FRACTAL-LIKE MERGING CHANNEL NETWORKS." Microscale Thermophysical Engineering 8, no. 3 (January 2004): 207–24. http://dx.doi.org/10.1080/10893950490477383.

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Sun, Chen-li, and Tzu-hsun Hsiao. "Quantitative analysis of microfluidic mixing using microscale schlieren technique." Microfluidics and Nanofluidics 15, no. 2 (February 15, 2013): 253–65. http://dx.doi.org/10.1007/s10404-013-1148-2.

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VERGUET, STÉPHANE, CHUANHUA DUAN, ALBERT LIAU, VEYSEL BERK, JAMIE H. D. CATE, ARUN MAJUMDAR, and ANDREW J. SZERI. "Mechanics of liquid–liquid interfaces and mixing enhancement in microscale flows." Journal of Fluid Mechanics 652 (May 19, 2010): 207–40. http://dx.doi.org/10.1017/s0022112009994113.

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Experimental work on mixing in microfluidic devices has been of growing importance in recent years. Interest in probing reaction kinetics faster than the minute or hour time scale has intensified research in designing microchannel devices that would allow the reactants to be mixed on a time scale faster than that of the reaction. Particular attention has been paid to the design of microchannels in order to enhance the advection phenomena in these devices. Ultimately, in vitro studies of biological reactions can now be performed in conditions that reflect their native intracellular environments. Liau et al. (Anal. Chem., vol. 77, 2005, p. 7618) have demonstrated a droplet-based microfluidic mixer that induces improved chaotic mixing of crowded solutions in milliseconds due to protrusions (‘bumps’) on the microchannel walls. Liau et al. (2005) have shown it to be possible to mix rapidly plugs of highly concentrated protein solutions such as bovine hemoglobin and bovine serum albumin. The present work concerns an analysis of the underlying mechanisms of shear stress transfer at liquid–liquid interfaces and associated enhanced mixing arising from the protrusions along the channel walls. The role of non-Newtonian rheology and surfactants is also considered within the mixing framework developed by Aref, Ottino and Wiggins in several publications. Specifically, we show that proportional thinning of the carrier fluid lubrication layer at the bumps leads to greater advection velocities within the plugs, which enhances mixing. When the fluid within the plugs is Newtonian, mixing will be enhanced by the bumps if they are sufficiently close to one another. Changing either the rheology of the fluid within the plugs (from Newtonian to non-Newtonian) or modifying the mechanics of the carrier fluid-plug interface (by populating it with insoluble surfactants) alters the mixing enhancement.

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Zhou, Ran, Athira N. Surendran, Marcel Mejulu, and Yang Lin. "Rapid Microfluidic Mixer Based on Ferrofluid and Integrated Microscale NdFeB-PDMS Magnet." Micromachines 11, no. 1 (December 25, 2019): 29. http://dx.doi.org/10.3390/mi11010029.

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Ferrofluid-based micromixers have been widely used for a myriad of microfluidic industrial applications in biochemical engineering, food processing, and detection/analytical processes. However, complete mixing in micromixers is extremely time-consuming and requires very long microchannels due to laminar flow. In this paper, we developed an effective and low-cost microfluidic device integrated with microscale magnets manufactured with neodymium (NdFeB) powders and polydimethylsiloxane (PDMS) to achieve rapid micromixing between ferrofluid and buffer flow. Experiments were conducted systematically to investigate the effect of flow rate, concentration of the ferrofluid, and micromagnet NdFeB:PDMS mass ratio on the mixing performance. It was found that mixing is more efficient with lower total flow rates and higher ferrofluid concentration, which generate greater magnetic forces acting on both streamwise and lateral directions to increase the intermixing of the fluids within a longer residence time. Numerical models were also developed to simulate the mixing process in the microchannel under the same conditions and the simulation results indicated excellent agreements with the experimental data on mixing performance. Combining experimental measurements and numerical simulations, this study demonstrates a simple yet effective method to realize rapid mixing for lab-on-chip systems.

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Folkard, Andrew. "The Multi-Scale Layering-Structure of Thermal Microscale Profiles." Water 13, no. 21 (November 1, 2021): 3042. http://dx.doi.org/10.3390/w13213042.

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Thermal microstructure profiling is an established technique for investigating turbulent mixing and stratification in lakes and oceans. However, it provides only quasi-instantaneous, 1-D snapshots. Other approaches to measuring these phenomena exist, but each has logistic and/or quality weaknesses. Hence, turbulent mixing and stratification processes remain greatly under-sampled. This paper contributes to addressing this problem by presenting a novel analysis of thermal microstructure profiles, focusing on their multi-scale stratification structure. Profiles taken in two small lakes using a Self-Contained Automated Micro-Profiler (SCAMP) were analysed. For each profile, buoyancy frequency (N), Thorpe scales (LT), and the coefficient of vertical turbulent diffusivity (KZ) were determined. To characterize the multi-scale stratification, profiles of d2T/dz2 at a spectrum of scales were calculated and the number of turning points in them counted. Plotting these counts against the scale gave pseudo-spectra, which were characterized by the index D of their power law regression lines. Scale-dependent correlations of D with N, LT and KZ were found, and suggest that this approach may be useful for providing alternative estimates of the efficiency of turbulent mixing and measures of longer-term averages of KZ than current methods provide. Testing these potential uses will require comparison of field measurements of D with time-integrated KZ values and numerical simulations.

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Davidson, Max, Paul Dommersnes, Martin Markström, Jean-Francois Joanny, Mattias Karlsson, and Owe Orwar. "Fluid Mixing in Growing Microscale Vesicles Conjugated by Surfactant Nanotubes." Journal of the American Chemical Society 127, no. 4 (February 2005): 1251–57. http://dx.doi.org/10.1021/ja0451113.

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Dzwinel, W., W. Alda, M. Pogoda, and D. A. Yuen. "Turbulent mixing in the microscale: a 2D molecular dynamics simulation." Physica D: Nonlinear Phenomena 137, no. 1-2 (March 2000): 157–71. http://dx.doi.org/10.1016/s0167-2789(99)00177-3.

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Dürauer, Astrid, Stefanie Hobiger, Cornelia Walther, and Alois Jungbauer. "Mixing at the microscale: Power input in shaken microtiter plates." Biotechnology Journal 11, no. 12 (July 14, 2016): 1539–49. http://dx.doi.org/10.1002/biot.201600027.

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Zimmerman, William B., and P. C. Chatwin. "Statistical fluctuations due to microscale mixing in a diffusion layer." Environmetrics 6, no. 6 (November 1995): 665–75. http://dx.doi.org/10.1002/env.3170060614.

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Kim, Jin-Yeon, Aurelio Bellotti, Prasanth Alapati, Kimberly E. Kurtis, Jianmin Qu, and Laurence J. Jacobs. "Use of a non-collinear wave mixing technique to image internal microscale damage in concrete." Journal of Applied Physics 131, no. 14 (April 14, 2022): 145102. http://dx.doi.org/10.1063/5.0086194.

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This research demonstrates the feasibility of using a non-collinear wave mixing technique to image internal microscale damage throughout the interior volume of a relatively large (28 cm thick) concrete component. By exploiting the underlying mechanics of nonlinear wave mixing, it is possible to mix two incident waves with frequencies low enough to propagate without being scattered by the inherently heterogenous, concrete microstructure, while still being sensitive to damage features with length scales well below these incident wavelengths. For this study, scanning and imaging is accomplished by manually adjusting the locations of the two incident waves, while a knowledge of the wave speeds in concrete plus synchronization identifies the location of the mixing zone—the specific volume of concrete being imaged. The viability of the proposed technique is demonstrated by examining a concrete prism specimen with known, embedded internal microscale damage.

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Leu, T. S., and F. C. Ma. "Novel EHD-Pump Driven Micro Mixers." Journal of Mechanics 21, no. 3 (September 2005): 137–44. http://dx.doi.org/10.1017/s1727719100000575.

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AbstractNovel electrohydrodynamic (EHD) pump driven micro mixers are fabricated to study fluidic mixing in micro channels experimentally. Microscopic flow visualization experiments are presented to visualize microscale mixing in micro mixers. Mixing is achieved in a laminar flow by perturbing the main flow with EHD pumps in a micro channel. EHD pumps operate in a way to form cross-stream mixing mechanism by using either dc voltage or traveling wave signals. Experimental results show transverse or vortical cross-stream flows are generated within hundreds microns distance in the micro mixers, thereby increasing mixing.

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Kim, Chul-Kyu, and Joon-Yong Yoon. "Optimal design of groove shape on passive micromixer using design of experiment technique." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 231, no. 4 (April 6, 2016): 880–87. http://dx.doi.org/10.1177/0954408916640663.

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Passive micromixers are one of the parts used for the mixing of two or more fluids in micro-electro-mechanical system devices, and they have been developed for various types. Fluid mixing in microscale devices is essential in microfluidic applications; however, it is difficult to mix fluids in microchannels due to the slowness of the molecular diffusion process at the microscale. In this study, optimization of the groove shape geometries of a micromixer using response surface design was performed, and the mixing performance was investigated through a numerical analysis applied with the passive scalar method. The most useful parameters were determined to be the geometric parameters of optimization, such as groove depth, groove length, distance between grooves, and groove angle. Response surface design, a design of experiments technique, was applied to the optimization procedure. The mixing index and pressure drop are important factors for evaluating the micromixer performance. Through the response surface design, this study aims to affect the groove shape of a passive micromixer. Consequently, it was concluded that the groove length and distance between grooves improved the mixing performance and decreased the pressure drop. In addition, optimal models were proposed for the passive micromixer.

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Jarecka, Dorota, Wojciech W. Grabowski, and Hanna Pawlowska. "Modeling of Subgrid-Scale Mixing in Large-Eddy Simulation of Shallow Convection." Journal of the Atmospheric Sciences 66, no. 7 (July 1, 2009): 2125–33. http://dx.doi.org/10.1175/2009jas2929.1.

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Abstract This paper discusses an extension of the approach proposed previously to represent the delay of cloud water evaporation and buoyancy reversal due to the cloud–environment mixing in bulk microphysics large-eddy simulation of clouds. In the original approach, an additional equation for the mean spatial scale of cloudy filaments was introduced to represent the progress toward microscale homogenization of a volume undergoing turbulent cloud–environment mixing, with the evaporation of cloud water allowed only when the filament scale approached the Kolmogorov microscale. Here, it is shown through a posteriori analysis of model simulations that one should also predict the volume fraction of the cloudy air that was diagnosed in the original approach. The resulting model of turbulent mixing and homogenization, referred to as the λ–β model, is applied in a series of shallow convection simulations using various spatial resolutions and compared to the traditional bulk model. This work represents an intermediate step in the development of a modeling framework to simulate characteristics of microphysical transformations during entrainment and subgrid-scale turbulent mixing.

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Zhang, Tina, Paul Costigan, Nitin Varshney, and Antonio Tricoli. "Disposable micro stir bars by photodegradable organic encapsulation of hematite–magnetite nanoparticles." RSC Advances 6, no. 40 (2016): 33843–50. http://dx.doi.org/10.1039/c5ra22082c.

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Zhang, Meng, Yunfeng Cui, Weihua Cai, Zhengwei Wu, Yongyao Li, Fengchen Li, and Wu Zhang. "High Mixing Efficiency by Modulating Inlet Frequency of Viscoelastic Fluid in Simplified Pore Structure." Processes 6, no. 11 (November 1, 2018): 210. http://dx.doi.org/10.3390/pr6110210.

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Fluid mixing plays an essential role in microscale flow systems. Here, we propose an active mixing approach which enhances the mixing of viscoelastic fluid flow in a simplified pore T-junction structure. Mixing is actively controlled by modulating the driving pressure with a sinusoidal signal at the two inlets of the T-junction. The mixing effect is numerically investigated for both Newtonian and viscoelastic fluid flows under different pressure modulation conditions. The result shows that a degree of mixing as high as 0.9 is achieved in viscoelastic fluid flows through the T-junction mixer when the phase difference between the modulated pressures at the two inlets is 180°. This modulation method can also be used in other fluid mixing devices.

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Granados-Ortiz, Francisco-Javier, and Joaquín Ortega-Casanova. "Mechanical Characterisation and Analysis of a Passive Micro Heat Exchanger." Micromachines 11, no. 7 (July 9, 2020): 668. http://dx.doi.org/10.3390/mi11070668.

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Heat exchangers are widely used in many mechanical, electronic, and bioengineering applications at macro and microscale. Among these, the use of heat exchangers consisting of a single fluid passing through a set of geometries at different temperatures and two flows in T-shape channels have been extensively studied. However, the application of heat exchangers for thermal mixing over a geometry leading to vortex shedding has not been investigated. This numerical work aims to analyse and characterise a heat exchanger for microscale application, which consists of two laminar fluids at different temperature that impinge orthogonally onto a rectangular structure and generate vortex shedding mechanics that enhance thermal mixing. This work is novel in various aspects. This is the first work of its kind on heat transfer between two fluids (same fluid, different temperature) enhanced by vortex shedding mechanics. Additionally, this research fully characterise the underlying vortex mechanics by accounting all geometry and flow regime parameters (longitudinal aspect ratio, blockage ratio and Reynolds number), opposite to the existing works in the literature, which usually vary and analyse blockage ratio or longitudinal aspect ratio only. A relevant advantage of this heat exchanger is that represents a low-Reynolds passive device, not requiring additional energy nor moving elements to enhance thermal mixing. This allows its use especially at microscale, for instance in biomedical/biomechanical and microelectronic applications.

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Plouffe, Patrick, Arturo Macchi, and Adam A. Donaldson. "Enhancement of Interphase Transport in Mini-/Microscale Applications Using Passive Mixing." Heat Transfer Engineering 34, no. 2-3 (January 2013): 159–68. http://dx.doi.org/10.1080/01457632.2013.703476.

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Taylor, David P., and Govind V. Kaigala. "Reconfigurable microfluidics: real-time shaping of virtual channels through hydrodynamic forces." Lab on a Chip 20, no. 10 (2020): 1720–28. http://dx.doi.org/10.1039/d0lc00197j.

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Virtual microfluidic channels, formed through hydrodynamic focusing within a 2D flow cell, enable the dynamic implementation of key microfluidic functionalities, such as the precise guiding, splitting, merging and mixing of microscale flows.

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Awoyera, Paul O., Oyinkansola Awobayikun, Ravindran Gobinath, and Emmanuel I. Ugwu. "Rheological, Mineralogical and Strength Variability of Concrete due to Construction Water Impurities." International Journal of Engineering Research in Africa 48 (May 2020): 78–91. http://dx.doi.org/10.4028/www.scientific.net/jera.48.78.

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Various national and international standards recommend potable water for mixing concrete; however, the availability of potable water is virtually a daunting task in some developing communities. Concrete workers in such environments tend to utilize any available water for mixing concrete, and this may be detrimental to the quality of the concrete being produced. This study investigates the rheological, mineralogical and strength variability of concrete due to construction water impurities. Water samples were collected from four different construction sites within Southwestern region of Nigeria for production of concrete. The physical and chemical properties of the waters were determined so as to measure their rate of contamination, prior to their use for mixing concrete. The rheological properties of the fresh concrete, compressive strength, split tensile strength, and microscale features of hardened concrete, that were produced with each water sample were determined. From the results, the rheological features of concrete were found not to be affected by water impurities, however, the mechanical test results revealed about 10% reduction in strength between concrete made with water having least and higher concentration of impurities. Also, it was evident from the microscale tests that the water impurities do alter the hydration rate of concrete, which results in strength reduction. The study suggests pretreatment of concrete mixing water before use in order to avoid its damaging effect on concrete life.

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Mizonov, V., E. Barantseva, Y. Khokhlova, H. Berthiaux, and C. Gatumel. "Theoretical Study of Superposition of Macro- and Microscale Mixing and its Influence on Mixing Kinetics and Mixture Quality." Particulate Science and Technology 27, no. 4 (July 2009): 327–36. http://dx.doi.org/10.1080/02726350902991015.

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Zhang, Chenshuo, Zifei Fan, Anzhu Xu, and Guangyan Hu. "Microscale Investigations of Mixing in a Matrix-Fracture Medium for Intermixing Displacement." Chemistry and Technology of Fuels and Oils 53, no. 2 (May 2017): 227–32. http://dx.doi.org/10.1007/s10553-017-0798-2.

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Naveira Garabato, Alberto C., Kurt L. Polzin, Raffaele Ferrari, Jan D. Zika, and Alexander Forryan. "A Microscale View of Mixing and Overturning across the Antarctic Circumpolar Current." Journal of Physical Oceanography 46, no. 1 (January 2016): 233–54. http://dx.doi.org/10.1175/jpo-d-15-0025.1.

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AbstractThe relative roles of isoneutral stirring by mesoscale eddies and dianeutral stirring by small-scale turbulence in setting the large-scale temperature–salinity relation of the Southern Ocean against the action of the overturning circulation are assessed by analyzing a set of shear and temperature microstructure measurements across Drake Passage in a “triple decomposition” framework. It is shown that a picture of mixing and overturning across a region of the Antarctic Circumpolar Current (ACC) may be constructed from a relatively modest number of microstructure profiles. The rates of isoneutral and dianeutral stirring are found to exhibit distinct, characteristic, and abrupt variations: most notably, a one to two orders of magnitude suppression of isoneutral stirring in the upper kilometer of the ACC frontal jets and an order of magnitude intensification of dianeutral stirring in the subpycnocline and deepest layers of the ACC. These variations balance an overturning circulation with meridional flows of O(1) mm s−1 across the ACC’s mean thermohaline structure. Isoneutral and dianeutral stirring play complementary roles in balancing the overturning, with isoneutral processes dominating in intermediate waters and the Upper Circumpolar Deep Water and dianeutral processes prevailing in lighter and denser layers.

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Zhao, Yu, Jiawei Li, Menglei Zhang, Yangyang Zhao, Jianglin Zou, and Tao Chen. "Phase-unwrapping algorithm combined with wavelet transform and Hilbert transform in self-mixing interference for individual microscale particle detection." Chinese Optics Letters 21, no. 4 (2023): 041204. http://dx.doi.org/10.3788/col202321.041204.

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DRAZEN, DAVID A., and W. KENDALL MELVILLE. "Turbulence and mixing in unsteady breaking surface waves." Journal of Fluid Mechanics 628 (June 1, 2009): 85–119. http://dx.doi.org/10.1017/s0022112009006120.

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Laboratory measurements of the post-breaking velocity field due to unsteady deep-water breaking are presented. Digital particle image velocimetry (DPIV) is used to measure the entire post-breaking turbulent cloud with high-resolution imagery permitting the measurement of scales fromO(1m) down toO(1mm). Ensemble-averaged quantities including mean velocity, turbulent kinetic energy (TKE) density and Reynolds stress are presented and compare favourably with the results of Melville, Veron & White (J. Fluid Mech., vol. 454, 2002, pp. 203–233; MVW). However, due to limited resolution, MVW's measurements were not spatially coherent across the turbulent cloud, and this restricted their ability to compute turbulent wavenumber spectra. Statistical spatial quantities including the integral length scaleL11, Taylor microscale λfand the Taylor microscale Reynolds numberReλare presented. Estimation of an eddy viscosity for the breaking event is also given based on analysis of the image data. Turbulent wavenumber spectra are computed and within 12 wave periods after breaking exhibit what have been termed ‘spectral bumps’ in the turbulence literature. These local maxima in the spectra are thought to be caused by an imbalance between the transport of energy from large scales and the dissipation at small scales. Estimates of the dissipation rate per unit mass are computed using both direct and indirect methods. Horizontally averaged terms in the TKE budget are also presented up to 27 wave periods after breaking and are discussed with regard to the dynamics of the post-breaking flow. Comparisons of the TKE density in the streamwise and cross-stream planes with the three-dimensional full TKE density are given in an appendix.

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Gao, Shang, Xichuan Rui, Xiangyu Zeng, and Jia Zhou. "EWOD Chip with Micro-Barrier Electrode for Simultaneous Enhanced Mixing during Transportation." Sensors 23, no. 16 (August 11, 2023): 7102. http://dx.doi.org/10.3390/s23167102.

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Digital microfluidic platforms have been extensively studied in biology. However, achieving efficient mixing of macromolecules in microscale, low Reynolds number fluids remains a major challenge. To address this challenge, this study presents a novel design solution based on dielectric electro-wetting (EWOD) by optimizing the geometry of the transport electrode. The new design integrates micro-barriers on the electrodes to generate vortex currents that promote mixing during droplet transport. This design solution requires only two activation signals, minimizing the number of pins required. The mixing performance of the new design was evaluated by analyzing the degree of mixing inside the droplet and quantifying the motion of the internal particles. In addition, the rapid mixing capability of the new platform was demonstrated by successfully mixing the sorbitol solution with the detection solution and detecting the resulting reaction products. The experimental results show that the transfer electrode with a micro-barrier enables rapid mixing of liquids with a six-fold increase in mixing efficiency, making it ideal for the development of EWOD devices.

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Radko, Timour. "Thermohaline layering on the microscale." Journal of Fluid Mechanics 862 (January 14, 2019): 672–95. http://dx.doi.org/10.1017/jfm.2018.976.

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A theoretical model is developed which illustrates the dynamics of layering instability, frequently realized in ocean regions with active fingering convection. Thermohaline layering is driven by the interplay between large-scale stratification and primary double-diffusive instabilities operating at the microscale – temporal and spatial scales set by molecular dissipation. This interaction is described by a combination of direct numerical simulations and an asymptotic multiscale model. The multiscale theory is used to formulate explicit and dynamically consistent flux laws, which can be readily implemented in large-scale analytical and numerical models. Most previous theoretical investigations of thermohaline layering were based on the flux-gradient model, which assumes that the vertical transport of density components is uniquely determined by their local background gradients. The key deficiency of this approach is that layering instabilities predicted by the flux-gradient model have unbounded growth rates at high wavenumbers. The resulting ultraviolet catastrophe precludes the analysis of such basic properties of layering instability as its preferred wavelength or the maximal growth rate. The multiscale model, on the other hand, incorporates hyperdiffusion terms that stabilize short layering modes. Overall, the presented theory carries the triple advantage of (i) offering an explicit description of the interaction between microstructure and layering modes, (ii) taking into account the influence of non-uniform stratification on microstructure-driven mixing, and (iii) avoiding unphysical behaviour of the flux-gradient laws at small scales. While the multiscale approach to the parametrization of time-dependent small-scale processes is illustrated here on the example of fingering convection, we expect the proposed technique to be readily adaptable to a wide range of applications.

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HO, CHIH-MING, and YITSHAK ZOHAR. "The PVC technique – a method to estimate the dissipation length scale in turbulent flows." Journal of Fluid Mechanics 352 (December 10, 1997): 135–59. http://dx.doi.org/10.1017/s0022112097007180.

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A time-averaged length scale can be defined by a pair of successive turbulent-velocity derivatives, i.e. [dnu(x)/ dxn]′/ [dn+1u(x)/ dxn+1]′. The length scale associated with the zeroth- and the first-order derivatives, u′/u′x, is the Taylor microscale. In isotropic turbulence, this scale is the average length between zero crossings of the velocity signal. The average length between zero crossings of the first velocity derivative, i.e. u′x/u′xx, can be reliably obtained by using the peak-valley-counting (PVC) technique. We have found that the most probable scale, rather than the average, equals the wavelength at the peak of the dissipation spectrum in a plane mixing layer (Zohar & Ho 1996). In this study, we experimentally investigate the generality of applying the PVC technique to estimate the dissipation scale in three basic turbulent shear flows: a flat-plate boundary layer, a wake behind a two-dimensional cylinder and a plane mixing layer. We also analytically explore the quantitative relationships among this length scale and the Kolmogorov and Taylor microscales.

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Davidovits, S., C. R. Weber, and D. S. Clark. "Modeling ablator grain structure impacts in ICF implosions." Physics of Plasmas 29, no. 11 (November 2022): 112708. http://dx.doi.org/10.1063/5.0107534.

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High-density carbon is a leading ablator material for inertial confinement fusion (ICF). This and some other ablator materials have grain structure which is believed to introduce very small-scale (∼nm) density inhomogeneity. In principle, such inhomogeneity can affect key ICF metrics like fuel compression and yield, by, for example, acting as a seed for instabilities and inducing mix between ablator and fuel. However, assessments of such effects are uncertain due to the difficulty of modeling this small-scale structure in ICF simulations, typically requiring reduced-resolution modeling that scales these features. We present a grain model and show both the impact of de-resolving grains and the complex mixing dynamics such structures can induce. We find that different methods for de-resolving grains can yield both different total deposition of kinetic energy perturbations and different fuel–ablator mixing. We then show a simple-to-implement approach for approximately conserving the deposition of perturbed kinetic energy and demonstrate that, for the present grain model and test cases, this approach yields a reasonably matched time history of mix width between less and more resolved grain models. The simulations here also demonstrate the complex interaction history between grain-induced mixing and instability around the fuel–ablator interface, showing, for example, that the grain-induced perturbations typically trigger instability of conduction-driven density gradients in the DT fuel, enhancing mix penetration early in the acceleration of the shell. Simulating both microscale and nanoscale grains, we find initial evidence for larger mixing in the microscale case of the present model, despite smaller deposited kinetic energy perturbation.

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Sinha, Akash, M. Zunaid, Sulekh Tokas, and Mubashshir Ahmad Ansari. "Numerical study of microscale passive mixing in a 3-Dimensional spiral mixer design." Materials Today: Proceedings 56 (2022): 851–56. http://dx.doi.org/10.1016/j.matpr.2022.02.508.

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Shi, Yanxiang, Vishwanath Somashekar, Rodney O. Fox, and Michael G. Olsen. "Visualization of turbulent reactive mixing in a planar microscale confined impinging-jet reactor." Journal of Micromechanics and Microengineering 21, no. 11 (October 5, 2011): 115006. http://dx.doi.org/10.1088/0960-1317/21/11/115006.

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Sun, Chen-li, and Tzu-hsun Hsiao. "On the background design for microscale background-oriented schlieren measurements of microfluidic mixing." Microfluidics and Nanofluidics 17, no. 2 (December 17, 2013): 375–91. http://dx.doi.org/10.1007/s10404-013-1309-3.

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Qian, Jin-yuan, Xiao-juan Li, Zhi-xin Gao, and Zhi-jiang Jin. "Mixing Efficiency Analysis on Droplet Formation Process in Microchannels by Numerical Methods." Processes 7, no. 1 (January 11, 2019): 33. http://dx.doi.org/10.3390/pr7010033.

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Liquid–liquid two-phase flow in microchannels has attracted much attention, due to the superiority of mass transfer enhancement. One of the biggest unresolved challenges is the low mixing efficiency at the microscale. Suitable mixing efficiency is important to promote the mass transfer of two-phase flow in microchannels. In this paper, the mixing efficiency in three junction configurations, including a cross-shaped junction, a cross-shaped T-junction, and a T-junction, is investigated by the volume of fluid (VOF) method coupled with user-defined scalar (UDS) model. All three junction configurations are designed with the same hydraulic diameter of 100 μm. Mixing components are distributed in the front and back parts of the droplet. The mixing efficiency in the droplet forming stage and the droplet moving stage are compared quantitatively. Results show that different junction configurations create very different mixing efficiencies, and the cross-shaped T-junction performs best, with relatively lower disperse phase fractions. However, with an increase of the disperse phase fraction, the cross-shaped junction is superior.

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Hu, Qingming, Jianhua Guo, Zhongliang Cao, and Hongyuan Jiang. "Asymmetrical Induced Charge Electroosmotic Flow on a Herringbone Floating Electrode and Its Application in a Micromixer." Micromachines 9, no. 8 (August 7, 2018): 391. http://dx.doi.org/10.3390/mi9080391.

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Enhancing mixing is of significant importance in microfluidic devices characterized by laminar flows and low Reynolds numbers. An asymmetrical induced charge electroosmotic (ICEO) vortex pair generated on the herringbone floating electrode can disturb the interface of two-phase fluids and deliver the fluid transversely, which could be exploited to accomplish fluid mixing between two neighbouring fluids in a microscale system. Herein we present a micromixer based on an asymmetrical ICEO flow induced above the herringbone floating electrode array surface. We investigate the average transverse ICEO slip velocity on the Ridge/Vee/herringbone floating electrode and find that the microvortex generated on the herringbone electrode surface has good potential for mixing the miscible liquids in microfluidic systems. In addition, we explore the effect of applied frequencies and bulk conductivity on the slip velocity above the herringbone floating electrode surface. The high dependence of mixing performance on the floating electrode pair numbers is analysed simultaneously. Finally, we investigate systematically voltage intensity, applied frequencies, inlet fluid velocity and liquid conductivity on the mixing performance of the proposed device. The microfluidic micromixer put forward herein offers great opportunity for fluid mixing in the field of micro total analysis systems.

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36

Rouhi, Omid, Sajad Razavi Bazaz, Hamid Niazmand, Fateme Mirakhorli, Sima Mas-hafi, Hoseyn A. Amiri, Morteza Miansari, and Majid Ebrahimi Warkiani. "Numerical and Experimental Study of Cross-Sectional Effects on the Mixing Performance of the Spiral Microfluidics." Micromachines 12, no. 12 (November 29, 2021): 1470. http://dx.doi.org/10.3390/mi12121470.

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Mixing at the microscale is of great importance for various applications ranging from biological and chemical synthesis to drug delivery. Among the numerous types of micromixers that have been developed, planar passive spiral micromixers have gained considerable interest due to their ease of fabrication and integration into complex miniaturized systems. However, less attention has been paid to non-planar spiral micromixers with various cross-sections and the effects of these cross-sections on the total performance of the micromixer. Here, mixing performance in a spiral micromixer with different channel cross-sections is evaluated experimentally and numerically in the Re range of 0.001 to 50. The accuracy of the 3D-finite element model was first verified at different flow rates by tracking the mixing index across the loops, which were directly proportional to the spiral radius and were hence also proportional to the Dean flow. It is shown that higher flow rates induce stronger vortices compared to lower flow rates; thus, fewer loops are required for efficient mixing. The numerical study revealed that a large-angle outward trapezoidal cross-section provides the highest mixing performance, reaching efficiencies of up to 95%. Moreover, the velocity/vorticity along the channel length was analyzed and discussed to evaluate channel mixing performance. A relatively low pressure drop (<130 kPa) makes these passive spiral micromixers ideal candidates for various lab-on-chip applications.

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37

Shi, Yanxiang, Rodney O. Fox, and Michael G. Olsen. "Confocal imaging of laminar and turbulent mixing in a microscale multi-inlet vortex nanoprecipitation reactor." Applied Physics Letters 99, no. 20 (November 14, 2011): 204103. http://dx.doi.org/10.1063/1.3662042.

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38

Ronen, Daniel, Mordeckai Magaritz, and Nathan Paldor. "Microscale haline convection-A proposed mechanism for transport and mixing at the water table region." Water Resources Research 24, no. 7 (July 1988): 1111–17. http://dx.doi.org/10.1029/wr024i007p01111.

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Williams, Ian S. "Some observations on the use of zircon U-Pb geochronology in the study of granitic rocks." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 83, no. 1-2 (1992): 447–58. http://dx.doi.org/10.1017/s0263593300008129.

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ABSTRACTIn situ, microscale, U-Pb isotopic analyses of zircon using the SHRIMP ion microprobe demonstrate both the potential and the limitations of zircon U-Pb geochronology. Most zircons, whether from igneous or metamorphic rocks, need to be considered as mixed isotopic systems. In simple, young igneous rocks the mixing is principally between isotopically disturbed and undisturbed zircon. In polymetamorphic rocks, several generations of zircon growth can coexist, each with a different pattern of discordance. A similar situation exists for igneous rocks rich in inherited zircon, as these contain both melt-precipitated zircon and inherited components of several different ages. Microscale analysis by ion probe makes it possible to sample the record of provenance, age and metamorphic history commonly preserved within a single zircon population. It also indicates how the interpretation of conventionallymeasured bulk zircon isotopic compositions might be improved.

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Briggs, D. A., J. H. Ferziger, J. R. Koseff, and S. G. Monismith. "Entrainment in a shear-free turbulent mixing layer." Journal of Fluid Mechanics 310 (March 10, 1996): 215–41. http://dx.doi.org/10.1017/s0022112096001784.

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Results from a direct numerical simulation of a shear-free turbulent mixing layer are presented. The mixing mechanisms associated with the turbulence are isolated. In the first set of simulations, the turbulent mixing layer decays as energy is exchanged between the layers. Energy spectra with E(k) ∼ k2 and E(k) ∼ k4 dependence at low wavenumber are used to initialize the flow to investigate the effect of initial conditions. The intermittency of the mixing layer is quantified by the skewness and kurtosis of the velocity fields: results compare well with the shearless mixing layer experiments of Veeravalli & Warhaft (1989). Eddies of size of the integral scale (k3/2/∈) penetrate the mixing layer intermittently, transporting energy and causing the layer to grow. The turbulence in the mixing layer can be characterized by eddies with relatively large vertical kinetic energy and vertical length scale. In the second set of simulations, a forced mixing layer is created by continuously supplying energy in a local region to maintain a stationary kinetic energy profile. Assuming the spatial decay of r.m.s. velocity is of the form u &∞ yn, predictions of common two-equation turbulence models yield values of n ranging from -1.25 to -2.5. An exponent of -1.35 is calculated from the forced mixing layer simulation. In comparison, oscillating grid experiments yield decay exponents between n = -1 (Hannoun et al. 1989) and n = -1.5 (Nokes 1988). Reynolds numbers of 40 and 58, based on Taylor microscale, are obtained in the decaying and forced simulations, respectively. Components of the turbulence models proposed by Mellor & Yamada (1986) and Hanjalić & Launder (1972) are analysed. Although the isotropic models underpredict the turbulence transport, more complicated anisotropic models do not represent a significant improvement. Models for the pressure-strain tensor, based on the anisotropy tensor, performed adequately.

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Dutta, Diganta, Keifer Smith, and Xavier Palmer. "Long-Range ACEO Phenomena in Microfluidic Channel." Surfaces 6, no. 2 (April 20, 2023): 145–63. http://dx.doi.org/10.3390/surfaces6020011.

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Microfluidic devices are increasingly utilized in numerous industries, including that of medicine, for their abilities to pump and mix fluid at a microscale. Within these devices, microchannels paired with microelectrodes enable the mixing and transportation of ionized fluid. The ionization process charges the microchannel and manipulates the fluid with an electric field. Although complex in operation at the microscale, microchannels within microfluidic devices are easy to produce and economical. This paper uses simulations to convey helpful insights into the analysis of electrokinetic microfluidic device phenomena. The simulations in this paper use the Navier–Stokes and Poisson Nernst–Planck equations solved using COMSOL to determine the maximum attainable fluid velocity with an electric potential applied to the microchannel and the most suitable frequency or voltage to use for transporting the fluid. Alternating current electroosmosis (ACEO) directs and provides velocity to the ionized fluid. ACEO can also mix the fluid at low frequencies for the purpose of dispersing particles. DC electroosmosis (DCEO) applies voltage along the microchannel to create an electric field that ionizes fluid within the microchannel, making it a cost-effective method for transporting fluid. This paper explores a method for an alternate efficient utilization of microfluidic devices for efficient mixing and transportation of ionized fluid and analyzes the electrokinetic phenomena through simulations using the Navier–Stokes and Poisson Nernst–Planck equations. The results provide insights into the parameters at play for transporting the fluid using alternating current electroosmosis (ACEO) and DC electroosmosis (DCEO).

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42

Padman, L. "Near-surface mixing in a freshwater lake." Marine and Freshwater Research 42, no. 6 (1991): 655. http://dx.doi.org/10.1071/mf9910655.

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Mixing rates in the upper 10 m of a freshwater lake during the spring heating season are examined by means of fine-structure temperature profiles. Dissipation rate, eddy diffusivity, and vertical heat flux are estimated from 'Thorpe reordering' of measured temperature profiles, a technique that allows these parameters to be obtained from the energy-containing scales of the turbulence rather than from the much smaller scales at which kinetic energy dissipation and scalar diffusion actually occur. The estimated vertical heat fluxes agree reasonably well with the seasonal variability of the lake's total heat content and with the observed short-term variability in mixed-layer temperature. These results suggest that satisfactory estimates of turbulent vertical diffusivities in the surface mixing layer can be obtained from Thorpe reordering. This technique can be applied to data that are considerably simpler and cheaper to obtain than are the measurements of microscale shear required for the more usual 'dissipation' method. Concurrent measurements of vertically averaged shear from a nearby surface mooring are used to study the use of Richardson numbers as a parameter in diffusion models. It is shown that considerable mixing can occur even when the Richardson number based on vertical and temporal averages of shear and density gradient is much larger than the assumed critical value of O(1). Therefore, in regions where the shear and strain variances evaluated over a fixed vertical scale cannot be related either observationally or by means of modelled spectra to the unresolved high wave-number variances, the use of diffusivity parametrizations based on measured, averaged Richardson numbers cannot be justified.

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Rezaei, N., and A. Firoozabadi. "Macro- and Microscale Waterflooding Performances of Crudes which form w/o Emulsions upon Mixing with Brines." Energy & Fuels 28, no. 3 (February 26, 2014): 2092–103. http://dx.doi.org/10.1021/ef402223d.

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Yamamoto, Masaru. "Microscale simulations of Venus’ convective adjustment and mixing near the surface: Thermal and material transport processes." Icarus 211, no. 2 (February 2011): 993–1006. http://dx.doi.org/10.1016/j.icarus.2010.11.019.

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Pawlik, Grzegorz, Wojciech Radosz, Antoni Mitus, Jaroslaw Mysliwiec, Andrzej Miniewicz, Francois Kajzar, and Ileana Rau. "Holographic grating inscription in DR1: DNA-CTMA thin films: the puzzle of time scales." Open Chemistry 12, no. 8 (August 1, 2014): 886–92. http://dx.doi.org/10.2478/s11532-014-0543-1.

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AbstractWe study experimentally the dynamics of holographic inscription of gratings in DR1:DNA-CTMA thin films using a degenerate two-wave mixing (DTWM) setup in its initial phase (30 ms) and in a longer time interval (30 s). The temporal pattern of evolution of diffraction efficiency is complex, simple fitting procedures fail to reproduce the data. We point out that the complex dynamics can originate a large span of temporal scales, closely related to the microscale inhomogeneity of local free volume. Some of its hallmarks are found through Monte Carlo simulations.

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Worth, N. A., and T. B. Nickels. "Some characteristics of thin shear layers in homogeneous turbulent flow." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369, no. 1937 (February 28, 2011): 709–22. http://dx.doi.org/10.1098/rsta.2010.0297.

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Tomographic particle image velocimetry measurements of homogeneous isotropic turbulence that have been made in a large mixing tank facility at Cambridge are analysed in order to characterize thin highly sheared regions that have been observed. The results indicate that such regions coincide with regions of high enstrophy, dissipation and stretching. Large velocity jumps are observed across the width of these regions. The thickness of the shear layers seems to scale with the Taylor microscale, as has been suggested previously. The results discussed here concentrate on examining individual realizations rather than statistics of these regions.

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Wang, Haotian, Kai Yang, Hua Wang, Jingyuan Wu, and Qingtai Xiao. "Statistical Image Analysis on Liquid-Liquid Mixing Uniformity of Micro-Scale Pipeline with Chaotic Structure." Energies 16, no. 4 (February 19, 2023): 2045. http://dx.doi.org/10.3390/en16042045.

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The aim of this work is to introduce a novel statistical technique for quantifying the concentration field uniformity of the liquid-liquid mixing process within a micro-scale chaotic pipeline. For illustration, the microscale liquid-liquid mixer in which the inlet direction is parallel to the mixing unit is designed by using the chaotic pipeline with Baker map. Meanwhile, the non-uniformity coefficient method is adopted quantificationally instead of qualitatively estimating the concentration field uniformity of the chaotic micromixer based on uniform design theory and image analysis. Results show that the concentration distribution of the chaotic mixing process of liquid-liquid under various working conditions is obtained by solving the steady-state Navier–Stokes and diffusion convection equations. The average contribution ratio of the three basic mixing units of the chaotic Baker pipeline to the concentration field uniformity is approximately 6:3:1, which is calculated aligned with the fluid flow direction successively. The optimal mixing uniformity can be obtained as the initial velocity is 0.05 m/s and the diffusion coefficient is 5 × 10−9 m2/s, respectively. The reliability of the new method for estimating the concentration field uniformity parameters is explained from three dimensions. The statistical image analysis technique is illustrated to be reliable and effective in yielding accurate concentration field information of the simulated chaotic mixer. Furthermore, it can be adapted to examine a variety of concentration distribution issues in which concentrations are evaluated under distinct scales.

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Kozlu, H., B. B. Mikic, and A. T. Patera. "Turbulent Heat Transfer Augmentation Using Microscale Disturbances Inside the Viscous Sublayer." Journal of Heat Transfer 114, no. 2 (May 1, 1992): 348–53. http://dx.doi.org/10.1115/1.2911282.

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We report here on an experimental study of heat transfer augmentation in turbulent flow. Enhancement strategies employed in this investigation are based on the near-wall mixing processes induced in the sublayer through appropriate wall and near-wall streamwise-periodic disturbances. Experiments are performed in a low-turbulence wind-tunnel with a high-aspect-ratio rectangular channel having either (a) two-dimensional periodic microgrooves on the wall, or (b) two-dimensional microcylinders placed in the immediate vicinity of the wall. It is found that micro-disturbances placed inside the sublayer induce favorable heat-transport augmentation with respect to the smooth-wall case, in that near-analogous momentum and heat transfer behavior are preserved; a roughly commensurate increase in heat and momentum transport is termed favorable in that it leads to a reduction in the pumping power penalty at fixed heat removal rate. The study shows that this favorable performance of microcylinder-equipped channel flows is achieved for microcylinders placed inside y+ ≃20, implying a dependence of the optimal position and size on Reynolds number. For microgrooved channel flows, favorable augmentation is obtained for a wider range of Reynolds numbers; however, optimal enhancement still requires a matching of geometric perturbation with the sublayer scale.

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Pleskot, Krzysztof. "Sedimentological characteristics of debris flow Deposits within ice−cored moraine of Ebbabreen, central Spitsbergen." Polish Polar Research 36, no. 2 (June 1, 2015): 125–44. http://dx.doi.org/10.1515/popore-2015-0006.

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Abstract The Ebbabreen ice−cored moraine area is covered with a sediment layer of up to 2.5 m thick, which mostly consists of massive diamicton. Due to undercutting by lateral streams, debris flow processes have been induced in marginal parts of this moraine. It was recognized that the sedimentology of deposits within the deposition area of debris flows is the effect of: (1) the origin of the sediments, (2) the nature of the debris flow, and (3) post−debris flow reworking. Analysis of debris flow deposits in microscale (thin sections) suggests a common mixing during flow, even though a small amount of parent material kept its original structure. The mixing of sediments during flow leads to them having similar sedimentary characteristics across the deposition area regardless of local conditions (i.e. slope angle, water content, parent material lithology). After the deposition of sediments that were transported by the debris flow, they were then reworked by a further redeposition process, primarily related to meltwater stream action.

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Wood, M. G., P. F. Greenfield, T. Howes, M. R. Johns, and J. Keller. "Computational fluid dynamic modelling of wastewater ponds to improve design." Water Science and Technology 31, no. 12 (June 1, 1995): 111–18. http://dx.doi.org/10.2166/wst.1995.0470.

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Wastewater ponds are a popular treatment alternative in Australia, especially in the meat industry. However, increasingly stringent Australian environmental legislation is raising questions about the continued viability of ponds. Traditional design methods do not address the hydrodynamic problems (i.e. short-circuiting) nor can they predict the effects of measures like baffles or repositioning inlets or outlets to improve performance. This is because the microscale interactions between the fluid and solids, and the biological reactions are ignored. This paper presents a tool -- computational fluid dynamic (CFD) modelling and explores its potential as a new design tool for wastewater ponds. FIDAP, a finite element CFD program, is one of the new generation of commercial CFD packages available. This program has been used to qualitatively investigate the hydrodynamics of four pond systems. These models are limited to 2-dimensional (D), steady-state simulations in a laminar flow regime. They form the first step in the process to address the microscale fluid flow, mixing and biology in wastewater ponds. Considerably more modelling and validation work is yet to be done.

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Journal articles on the topic 'Mixing at Microscale'

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