Rapid mixing in microchannel using standing bulk acoustic waves
TL;DR: In this paper, an alternating multinode mixing method was proposed to enhance the mixing of fluids in a microchannel using ultrasonic waves, which was shown to reduce the mixing time by two orders of magnitude compared to diffusion.
Abstract: We present a technique for mixing the fluids in a microchannel using ultrasonic waves. Acoustic mixing is driven by the acoustic body force, which depends on the density gradient and speed of the sound gradient of the inhomogeneous fluid domain. In this work, mixing of fluids in a microchannel is achieved via an alternating multinode mixing method, which employs acoustic multinode standing waves of time-varying wavelengths at regular time intervals. The proposed technique is rapid, efficient, and found to enhance the mixing of fluids significantly. It is shown that the mixing time due to acoustic mixing (2–3 s) is reduced by two orders of magnitude compared to the mixing time only due to diffusion (400 s). Furthermore, we investigate the effects of the acoustic mixing on different fluid flow configurations and sound wave propagation directions as they have a direct influence on mixing time and have rarely been addressed previously. Remarkably, it is found that mixing performance is strongly dependent on the direction of the acoustic wave propagation. The acoustic field propagated parallel to the fluid-fluid interface mixes fluids rapidly (2–3 s) as compared to the acoustic field propagated perpendicular to the fluid-fluid interface (40 s).
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TL;DR: In this paper, the authors demonstrate theoretically that acoustic forces acting on inhomogeneous fluids can be used to pattern and manipulate solute concentration fields into spatio-temporally controllable configurations stabilized against gravity.
Abstract: We demonstrate theoretically that acoustic forces acting on inhomogeneous fluids can be used to pattern and manipulate solute concentration fields into spatio-temporally controllable configurations stabilized against gravity. A theoretical framework describing the dynamics of concentration fields that weakly perturb the fluid density and speed of sound is presented and applied to study manipulation of concentration fields in rectangular-channel acoustic eigenmodes and in Bessel-function acoustic vortices. In the first example, methods to obtain horizontal and vertical multi-layer stratification of the concentration field at the end of a flow-through channel are presented. In the second example, we demonstrate acoustic tweezing and spatio-temporal manipulation of a local high-concentration region in a lower-concentration medium, thereby extending the realm of acoustic tweezing to include concentration fields.
24 citations
TL;DR: In this paper , a review of microfluidic-based mixing methods capable of synthesizing nanoparticles is presented, with a detailed discussion on the practical applications of each method in improving the performance of fluid mixing.
Abstract: Microfluidic-based mixing methods have aroused increasing attention due to their tremendous potential in bio-related and materials science fields. Achieving mixing based on microscale devices, microfluidic-based mixing methods offer several advantages over their macroscale device-based counterparts, such as compact size, ease of operation, and the straightforward control of the mixing process. Generally, the ability to achieve high mixing performance in an efficient and simple manner is a key criterion for the reliability of a microfluidic-based method, which is essential to the reactor design. In the review paper, we summarize a number of microfluidic-based mixing methods capable of synthesizing nanoparticles. For comparative purposes, we divide these methods into active and passive methods, looking at their working principles as well as their respective advantages. On this basis, we present five commonly used active methods and three representative passive methods, with a detailed discussion on the practical applications of each method in improving the performance of fluid mixing. At the end of the review, we elaborate on some of current limitations and future prospects of these methods, which will help guide readers who are interested in making some innovations in this area of research.
14 citations
14 citations
TL;DR: In this paper, computational fluid dynamics and heat transfer (CFD/HT) analyses using a 3D volume of fluid model coupled with a phase-change model for the interfacial heat and mass transfer were performed for multiple microchannel configurations (constricted inlet, expanding, and auxiliary jetting microchannels).
Abstract: Microchannels are a promising solution for high-heat-flux thermal management scenarios, including high-performance microelectronics cooling and power electronics cooling. However, thermohydraulic instabilities result from the rapid vapor bubble formation. The prior literature has examined several methods, including constricted inlet microchannels, expanding microchannels, and auxiliary jetting microchannels, to mitigate the effect of these instabilities. Computational fluid dynamics and heat transfer (CFD/HT) modeling of the flow boiling phenomena in these microchannel configurations has seen limited examination, and one-to-one numerical comparisons of the different mitigation strategies have not been performed. In the present investigation, CFD/HT analyses using a three-dimensional (3D) volume of fluid model coupled with a phase-change model for the interfacial heat and mass transfer were performed for multiple microchannel configurations (constricted inlet, expanding, and auxiliary jetting microchannels). A benchmark case of a rectangular microchannel was examined to quantify baseline thermohydraulic performance. Results demonstrated slight to significant thermal performance improvements for all cases, and significant pressure benefits for the expanding and jetting cases, consistent with experimental results in the literature. Bubble dynamics and visualization for the baseline and alternative configurations are provided to give insight into their underlying physics, and the differences in performance were investigated and compared with available literature.
13 citations
TL;DR: In this paper, the effects of increasing an operating parameter on local mixing quality along the microchannels are investigated and a method for calculating local mixing efficiency is also characterized, showing that the mixing efficiency varies exponentially with the flow distance.
Abstract: A fast mixing is critical for subsequent practical development of microfluidic devices, which are often used for assays in the detection of reagents and samples. The present work sets up computational fluid dynamics simulations to explore the flow characteristic and mixing mechanism of fluids in cross-shaped mixers within the laminar regime. First, the effects of increasing an operating parameter on local mixing quality along the microchannels are investigated. It is found that sufficient diffusion cannot occur even though the concentration gradient is large at a high Reynolds number. Meanwhile, a method for calculating local mixing efficiency is also characterized. The mixing efficiency varies exponentially with the flow distance. Second, in order to optimize the cross-shaped mixer, the effects of design parameters, namely aspect ratio, mixing angle and blockage, on mixing quality are captured and the visualization of velocity and concentration distribution are demonstrated. The results show that the aspect ratio and the blockage play an important role in accelerating the mixing process. They can improve the mixing efficiency by increasing the mass transfer area and enhancing the chaotic advection, respectively. In contrast, the inflow angle that affects dispersion length is not an effective parameter. Besides, the surface roughness, which makes the disturbance of fluid flow by roughness more obvious, is considered. Three types of rough elements bring benefits for enhancing mixing quality due to the convection induced by the lateral velocity.
9 citations
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TL;DR: In this paper, the authors report the progress on the recent development of micromixers and present different types and designs of active and passive MCMs, as well as the operation points of the MCMs.
Abstract: This review reports the progress on the recent development of micromixers. The review first presents the different micromixer types and designs. Micromixers in this review are categorized as passive micromixers and active micromixers. Due to the simple fabrication technology and the easy implementation in a complex microfluidic system, passive micromixers will be the focus of this review. Next, the review discusses the operation points of the micromixers based on characteristic dimensionless numbers such as Reynolds number Re, Peclet number Pe, and in dynamic cases the Strouhal number St. The fabrication technologies for different mixer types are also analysed. Quantification techniques for evaluation of the performance of micromixers are discussed. Finally, the review addresses typical applications of micromixers.
1,651 citations
TL;DR: A review on microstructured mixer devices and their mixing principles concerning miscible liquids (and gases) is given in this article, supplemented by the description of typical mixing element designs, methods for mixing characterisation, and application fields.
1,354 citations
TL;DR: A three-dimensional serpentine microchannel design with a "C shaped" repeating unit is presented in this paper as a means of implementing chaotic advection to passively enhance fluid mixing.
Abstract: A three-dimensional serpentine microchannel design with a "C shaped" repeating unit is presented in this paper as a means of implementing chaotic advection to passively enhance fluid mixing. The device is fabricated in a silicon wafer using a double-sided KOH wet-etching technique to realize a three-dimensional channel geometry. Experiments using phenolphthalein and sodium hydroxide solutions demonstrate the ability of flow in this channel to mix faster and more uniformly than either pure molecular diffusion or flow in a "square-wave" channel for Reynolds numbers from 6 to 70. The mixing capability of the channel increases with increasing Reynolds number. At least 98% of the maximum intensity of reacted phenolphthalein is observed in the channel after five mixing segments for Reynolds numbers greater than 25. At a Reynolds number of 70, the serpentine channel produces 16 times more reacted phenolphthalein than a straight channel and 1.6 times more than the square-wave channel. Mixing rates in the serpentine channel at the higher Reynolds numbers are consistent with the occurrence of chaotic advection. Visualization of the interface formed in the channel between streams of water and ethyl alcohol indicates that the mixing is due to both diffusion and fluid stirring.
1,218 citations
TL;DR: The T-sensor as mentioned in this paper is a recently developed microfluidic chemical measurement device that exploits the low Reynolds number flow conditions in microfabricated channels, allowing measurement of analyte concentrations on a continuous basis.
Abstract: The T-sensor is a recently developed microfluidic chemical measurement device that exploits the low Reynolds number flow conditions in microfabricated channels. The interdiffusion and resulting chemical interaction of components from two or more input fluid streams can be monitored optically, allowing measurement of analyte concentrations on a continuous basis. In a simple form of T-sensor, the concentration of a target analyte is determined by measuring fluorescence intensity in a region where the analyte and a fluorescent indicator have interdiffused. An analytical model has been developed that predicts device behavior from the diffusion coefficients of the analyte, indicator, and analyte-indicator complex and from the kinetics of the complex formation. Diffusion coefficients depend on the local viscosity which, in turn, depends on local concentrations of all analytes. These relationships, as well as reaction equilibria, are often unknown. A rapid method for determining these unknown parameters by interpreting T-sensor experiments through the model is presented.
655 citations
28 Jan 2005
TL;DR: In this paper, the authors present a multifaceted, Hierarchical Analyser of Chemical Micro Process Technology (HIPT) with a focus on the impact of chemical micro processing on process results.
Abstract: Preface.List of Symbols and Abbreviations.1. A MULTI-FACETED, HIERARCHIC ANALYSIS OF CHEMICAL MICRO PROCESS TECHNOLOGY.1.1 Micro Reactor Differentiation and Process Intensification.1.2 Consequences of Chemical Micro Processing.1.3 Physical and Chemical Fundaments.1.4 Impact on Chemical Engineering.1.5 Impact on Process Engineering.1.6 Impact on Process Results.1.7 Impact on Society and Ecology.1.8 Impact on Economy.1.9 Application Fields and Markets of Micro Reactors.2. MODELLING AND SIMULATION OF MICRO REACTORS.2.1 Introduction.2.2 Flow Phenomena on the Micro Scale.2.3 Methods of Computational Fluid Dynamics.2.4 Flow Distributions.2.5 Heat Transfer.2.6 Mass Transfer and Mixing.2.7 Chemical Kinetics.2.8 Free Surface Flow.2.9 Transport in Porous Media.3. GAS-PHASE REACTIONS.3.1 Catalyst Coatings in Micro Channels: Techniques and Analytical Characterization.3.2 Micro Reactors for Gas-Phase Reactions.3.3 Oxidations.3.4 Hydrogenations.3.5 Dehydrogenations.3.6 Substitutions.3.7 Eliminations.3.8 Additions and Coupling Reactions.4. LIQUID- AND LIQUID/LIQUID-PHASE REACTIONS.
472 citations