TECHNIQUES TO ENHANCE FLUID MICRO-MIXING AND CHAOTIC MICROMIXERS

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1567-1570 ◽  
Author(s):  
Y. T. CHEW ◽  
H. M. XIA ◽  
C. SHU ◽  
S. Y. M. WAN
Keyword(s):  
Chaotic Advection ◽  
Chaotic Mixing ◽  
Inertial Effects ◽  
Passive Mixer ◽  
Poincaré Plot ◽  
Mixer Design ◽  
Recent Developments ◽  
Fast Development ◽  
Active Mixing ◽  
Working Mechanisms

With fast development of microfluidic systems, fluid micro-mixing becomes a very important issue. In this paper, recent developments on various micromixers and their working mechanisms are reviewed, including the external agitation methods applied in active mixing and the channel geometries adopted in passive mixer design. The chaotic mixing and the influences of Re would be mainly discussed. At moderate and high Re , the fluid inertial effects usually facilitate the chaotic mixing. At low Re , generation of chaotic advection becomes more difficult but can still be achieved through fluid manipulations such as stretching and folding. Chaotic mixers can be characterized using dynamical system techniques, such as Poincaré plot, and Lyapunov exponent.

Simulation of Two Designs of Micro-Mixers With Enhanced Advection Mechanisms

2011 ◽  
Author(s):  
S. A. Kazemi ◽  
M. Passandideh-Fard ◽  
J. Esmaeelpanah
Keyword(s):  
Numerical Study ◽  
Control Volume ◽  
Numerical Technique ◽  
Chaotic Advection ◽  
Mixing Efficiency ◽  
Mixing Length ◽  
Surface Development ◽  
Mixer Design ◽  
Gas Liquid Flow ◽  
Micro Mixer

In this paper, a numerical study of two new designs of passive micro-mixers based on chaotic advection is presented. The advection phenomenon in a T-shaped micro-mixer is enhanced using a segmented gas-liquid flow; and a peripheral/axial mixing mechanism. The simulations are performed for two non-reactive miscible gases: oxygen and methanol. The numerical model employed for this study is based on the solution of the physical governing equations namely the continuity, momentum, species transport and an equation to track the free surface development. The equations are discretized using a control volume numerical technique. The distribution of the species concentration within the domain is calculated based on which a mixing intensity factor is introduced. This factor is then used as a criterion for the mixing length. In the first micro-mixer design with a drop injection mechanism for a typical condition, the mixing length is reduced by nearly 15%. Compared to that of a simple T-shaped micro-mixer with the same flow rates, the two gases interface area is increased in axisymmetric micro-mixer leading to an increase of the mixing efficiency and a reduction of the mixing length. Also, the effects of the baffles height and span on the mixing efficiency and length in axisymmetric micro-mixer are studied. Having baffles in the channel can substantially decrease the mixing length.

Improved Serpentine Laminating Micromixer: Numerical Investigation and Experimental Verification

2007 ◽  
Author(s):  
Jang Min Park ◽  
Dong Sung Kim ◽  
Tae Gon Kang ◽  
Tai Hun Kwon
Keyword(s):  
Numerical Analysis ◽  
Experimental Verification ◽  
Flow Characteristics ◽  
Chaotic Advection ◽  
Intensity Change ◽  
Chaotic Mixing ◽  
Cross Sectional ◽  
Mixing Performance ◽  
Optical Micrograph ◽  
Particle Tracking Method

It is a difficult task to achieve an efficient mixing inside a microchannel since the flow is characterized by low Reynolds number (Re). Recently, the serpentine laminating micromixer (SLM) was reported to achieve an efficient chaotic mixing by introducing ‘F’-shape mixing units successively in two layers such that two chaotic mixing mechanisms, namely splitting/recombination and chaotic advection, enhance the mixing performance in combination. The present study describes an improved serpentine laminating micromixer (ISLM) with a novel redesign of the ‘F’-shape mixing unit. Reduced cross-sectional area at the recombination region of ISLM locally enhances advection effect which helps better vertical lamination, resulting in improved mixing performance. Flow characteristics and mixing performances of SLM and ISLM are investigated numerically and verified experimentally. Numerical analysis system is developed based on a finite element method and a colored particle tracking method, while mixing entropy is adopted as a quantitative mixing measure. Numerical analysis result confirms enhanced vertical lamination performance and consequently improved mixing performance of ISLM. For experimental verification, SLM and ISLM were fabricated by polydimethylsiloxane (PDMS) casting against SU-8 patterned masters. Mixing performance is observed by normalized red color intensity change of phenolphthalein along the downchannel. Flow characteristics of SLM and ISLM are investigated by tracing the red interface of two streams via optical micrograph. The normalized mixing intensity behavior confirms improved mixing performance of ISLM, which is consistent with numerical analysis result.

scholarly journals Numerical Analysis of Liquid Mixing in a T-Micromixer with Taylor Dispersion Obstructions

2019 ◽  
Vol 5 (1) ◽  
pp. 147-160
Author(s):  
T. Manoj Dundi ◽  
S. Chandrasekhar ◽  
Shasidar Rampalli ◽  
V. R. K. Raju ◽  
V. P. Chandramohan
Keyword(s):  
Biomedical Engineering ◽  
Flow Direction ◽  
Taylor Dispersion ◽  
Chaotic Advection ◽  
Mixing Enhancement ◽  
Chemical Processing ◽  
Inertial Effects ◽  
Mixing Performance ◽  
Velocity Gradients

Passive micromixers are of great importance in biomedical engineering (lab-on-chips) and chemical processing (microreactors) fields. Various hydrodynamic principles such as lamination, flow separation, and chaotic advection were employed previously to improve mixing in passive mixers. However, mixing enhancement due to velocity gradients in the flow, which is known as the Taylor dispersion effect, has been seldom studied. In the present study, thin rectangular slabs oriented in the flow direction are placed in the mixing channel of a T-micromixer. The thin rectangular slabs are referred to as Taylor Dispersion Obstructions (TDOs) as they are designed to create velocity gradients in the flow. The mixing performance of T-micromixer with and without TDOs is estimated in the Re range of 0 to 350. It is observed that there is no effect on mixing in the presence of TDOs in the low Re (0 < Re < 100), as the velocity gradients created in the flow are considerably small. The vortex formed in the flow for Re of 100 to 220 damped the gradients of velocity created in the flow (due to the presence of TDOs) which resulted in negligible improvement in the quality of mixing. However, considerable enhancement in mixing performance is obtained at high Re (250 to 350) with the presence of TDOs in the mixer. The increase in inertial effects at higher Recreated larger gradients of velocity near the walls of TDOs and mixing channel walls and thereby a significant enhancement in mixing performance is obtained due to Taylor dispersion.

Optimal parametric mixing analysis of active and passive micromixers using Taguchi method

2019 ◽  
Vol 233 (6) ◽  
pp. 1292-1303 ◽  
Author(s):  
Imran Shah ◽  
Han Su Jeon ◽  
Muhsin Ali ◽  
Doh Hoi Yang ◽  
Kyung-Hyun Choi
Keyword(s):  
Taguchi Method ◽  
Passive Mixer ◽  
External Energy ◽  
Mixing Index ◽  
Two Fluids ◽  
Active Mixer ◽  
Passive Mixing ◽  
Mixing Ability ◽  
Active Mixing ◽  
Micro Mixer

Mixing of fluids flowing through channels and chambers is a crucial step in chemical and biochemical reactions inside microfluidic devices due to laminar flow because of small size channel and chamber dimensions. Mixing can be enhanced by passive or active mechanism which makes convection dominant over diffusion. To address this challenge, the study proposes three novel mixing designs: passive mixer, active mixer and a combination of active and passive mixing. These designs mixing performance has been studied by numerical simulation using COMSOL 5.3. According to the preliminary results of the study, pure active micromixer design has superior mixing ability. The mixing ability was proved by concentration line plots, concentration contours and videos. In order to further optimize the mixing index of the pure active micromixer, Taguchi method is applied against various input parametric values for micromixer such as frequency, voltage and velocity. The velocity is required for two fluids to flow, while frequency and voltages are for providing an external energy for active mixing. A total of nine cases were analyzed; the two best cases out of nine were selected for comparing mixing index line plots. The result of the study conclude that pure active micro-mixer at an optimal set of parameters, frequency of 10 Hz, velocity of 0.05 mm s–1 and voltage of 0.5 V achieved 99.6% mixing index at t = 0.2 s.

scholarly journals A Novel High-Throughput Chaotic Advection Microreactor for the Preparation of Uniform BaSO4 Nanoparticles

2021 ◽  
Author(s):  
Hua Yang ◽  
Shi-Xiao Wei ◽  
Han Chen ◽  
Lang Chen ◽  
Chak-tong Au ◽  
...  
Keyword(s):  
High Throughput ◽  
Three Dimensional ◽  
Volumetric Flow Rate ◽  
Secondary Flows ◽  
Chaotic Advection ◽  
Narrow Particle Size Distribution ◽  
Chaotic Mixing ◽  
Mixing Efficiency ◽  
Size Uniformity ◽  
Average Size

Owing to high mixing efficiency, microreactors are used to synthesize uniform BaSO4 nanoparticles, but application in industrial scale is limited due to poor throughput. In this work, a high-throughput passive four-stage asymmetric oscillating feedback microreactor using chaotic mixing mechanism was developed to prepare BaSO4 nanoparticles of high size uniformity. Three-dimensional unsteady simulations showed that chaotic mixing could be induced by three unique secondary flows (i.e., vortex, recirculation, and oscillation), and the fluid oscillation mechanism was examined in detail. Simulations and Villermaux-Dushman experiments indicate that almost complete mixing in molecular level could be achieved when total volumetric flow rate Qtotal was larger than 10 mL/min, and the prepared BaSO4 nanoparticles were with narrow particle size distribution (PSD). Through the adjustment of Qtotal and reactant concentrations, it is easy to control the average size. An average size of 26 nm with narrow PSD could be achieved at Qtotal = 160 mL/min.

scholarly journals GATHERING E-EVIDENCE IN CROSS-BORDER CASES: RECENT DEVELOPMENTS IN EU LAW

2019 ◽  
Vol 32 (1) ◽  
pp. 155-162
Author(s):  
Aleksandar Chavleski ◽  
Goce Galev
Keyword(s):  
International Law ◽  
Digital Data ◽  
Digital Evidence ◽  
Criminal Cases ◽  
Cross Border ◽  
Foreign Countries ◽  
Recent Developments ◽  
Fast Development ◽  
Draft Regulation ◽  
Critical Overview

With the fast development of the digital technology, the need for efficient gathering of digital evidence in criminal cases has risen exponentially. Often, the digital data is stored on servers located abroad, so national authorities cannot obtain them without seeking legal aid from their counterparts in foreign country/territory. This cooperation often doesn’t work seamlessly not only from legal, but from factual reasons as well. Here series of questions regarding national sovereignty, jurisdiction and international law are intertwined. In order to achieve sufficient speed in processing such requests, national authorities tried to bypass their counterparts in foreign countries and communicated directly with the service provider. These investigations are time-sensitive in order both to secure the evidence and its integrity. In order to adequately address these concerns, in June 2016 the Council of EU called the Commission to prepare an e-evidence package, which was eventually presented in April 2018. The aim of this article will be to give a critical overview of the proposed package mainly via its key component – the draft Regulation.

On the advection of spherical and non-spherical particles in a non-uniform flow

1990 ◽  
Vol 333 (1631) ◽  
pp. 289-307 ◽  
Keyword(s):  
Settling Velocity ◽  
Fluid Velocity ◽  
Added Mass ◽  
Laminar Flows ◽  
Chaotic Advection ◽  
Spherical Particles ◽  
Inertial Effects ◽  
Gravitational Settling ◽  
Regular Motion ◽  
Velocity Gradients

Small spherical particles when introduced into a non-uniform or unsteady flow are usually subject to inertial effects, either of the particle mass or of the fluid added-mass, and the gravitational settling. Small non-spherical particles, even when inertial effects are negligible, turn in response to the local fluid velocity gradients and the settling velocity of a particle varies with its orientation. These features are distinct from the response of lagrangian elements which simply move with the local fluid velocity. In this paper these different responses for small, stokesian particles are considered for some example non-uniform laminar flows. It is noted that this added feature may lead to chaotic particle motion where the motion of lagrangian elements is regular, and conversely regular motion where there is chaotic advection of lagrangian elements.

Forest Industry Anaerobic Wastewater Treatment and its Future Development

1985 ◽  
Vol 17 (1) ◽  
pp. 265-270
Author(s):  
Juhani Orivuori
Keyword(s):  
Wastewater Treatment ◽  
Private Enterprise ◽  
Anaerobic Treatment ◽  
Full Scale ◽  
Forest Industry ◽  
Anaerobic Wastewater Treatment ◽  
Recent Developments ◽  
Fast Development ◽  
Future Demands

Very few methods have been developed with such speed as anaerobic wastewater treatment. Universities, Government agencies, private enterprise and scientists all over the world are using millions of dollars in studies, pilot and full scale experiments trying to find the most practical anaerobic treatment systems for various wastewaters. The follow-up alone of all the information published in this field would require an institute of its own. Commercial interests are driving private enterprise to fast development of full scale treatment plants. In this paper the reasons for this interest in anaerobic treatment are focused on in the light of the recent developments in knowledge of the quality and quantity of forest industry wastewaters. Future wastewater characteristics and the possibility of anaerobic treatment to meet future demands are discussed. The need for co-operation between forest industry process engineers and wastewater treatment specialists is emphasized in order to optimize internal and external pollution control methods.

Inertial effects in chaotic mixing with diffusion

1995 ◽  
Vol 285 (-1) ◽  
pp. 1 ◽  
Author(s):  
Pradip Dutta ◽  
Rene Chevray
Keyword(s):  
Chaotic Mixing ◽  
Inertial Effects

Finite Time Lyapunov Exponent for Micro Chaotic Mixer Design

2003 ◽  
Author(s):  
Xi-Ze Niu ◽  
Patrick Tabeling ◽  
Yi-Kuen Lee
Keyword(s):  
Lyapunov Exponent ◽  
Finite Time ◽  
Stokes Equations ◽  
Channel Length ◽  
Navier Stokes ◽  
Chaotic Mixing ◽  
Mixing Efficiency ◽  
Navier Stokes Equations ◽  
Finite Time Lyapunov Exponent ◽  
Mixer Design

In this paper, the Finite Time Lyapunov Exponent (FTLE) approach is used to analyze and optimize chaotic mixing in an active microchannel and a static mixer. The characteristics of FTLE related to chaotic mixing are discussed. By comparing the similarity of Poincare´ mapping and FTLE contour, it is shown that FTLE can be used to evaluate the chaotic mixing of liquid in the micromixer qualitatively and quantitatively. The minimum channel length needed for full mixing in the mixers can be estimated by the mean FTLE. The results are consistent with CFD simulations directly solving the Navier-Stokes equations coupled with the diffusion equation. More than 3 orders of CPU time can be saved by using FTLE compared with the classical infinite time Lyapunov exponent approach. Moreover, the FTLE is used to optimize the design and operation of the chaotic micromixers to improve the mixing efficiency for the first time.

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