A New Scheme for Improving the Mixing Efficiency in Micro Scale

2011 ◽  
Author(s):  
Ali Mohammad Anbari ◽  
Artin Haroutunian ◽  
Mohammed Said Saidi ◽  
Mohammad Behshad Shafii
Keyword(s):  
Fluid Velocity ◽  
Mixing Efficiency ◽  
Mixing Process ◽  
Layer Potential ◽  
Outlet Cross Section ◽  
Micro Scale ◽  
Two Fluids ◽  
Mixing Chamber ◽  
Micro Channels ◽  
Micro Mixer

Generally speaking, most micro-fluidic mixing systems are limited to the low Reynolds number regime in which diffusion dominates convection, and consequently the mixing process tends to be slow and it takes a relatively long time to have two fluids completely mixed. Therefore, rapid mixing is essential in micro-fluidic systems. In order to hasten the mixing process in micro scale, in this study we come up with a novel scheme for a two dimensional micro-fluidic mixer which encompasses three pairs of electrodes, one pair embedded in the mixing chamber and two pairs located in the micro-channels before and after the mixing chamber. The width of the middle pair is assumed to be twice of the other pairs. In addition, the fluids enter the device via two different entrances within a T-junction. The width of all micro-channels is equal to 50 micrometer and the whole mixer is less than 1 millimeter in length. While Electrical potentials are applied to three electrodes in the outlet and inlet ports in order to conduct the fluids within the mixer, the chaotic electrical fields applied to the mixing chamber are derived by the Duffing-Holmes nonlinear system. We numerically simulate the performance of our micro-mixer by solving Navier-Stokes and continuity equations for fluid velocity field, Poisson-Boltzmann equation for describing the electrical double layer potential distribution, Laplace equation for the externally induced electrical field distribution and concentration transport equation in order to obtain the concentration distribution of two fluids within the geometry. Then, the mixing efficiency is calculated in the outlet cross section of the mixer and the results indicate that a mixing performance efficiency of up to 98% is obtainable by utilizing this proposed scheme.

A Study on Mixing Efficiency in a Two-Channel Circular Micromixer

2006 ◽  
Vol 22 (4) ◽  
pp. 331-338
Author(s):  
M. Chang ◽  
Y.-H. Hu ◽  
S.-W. Chau ◽  
K.-H. Lin
Keyword(s):  
Three Dimensional ◽  
Numerical Prediction ◽  
Mixing Efficiency ◽  
Experimental Measurements ◽  
Inspection Method ◽  
Flow Rates ◽  
Two Fluids ◽  
Finite Volume Discretization ◽  
Mixing Chamber ◽  
Image Inspection

AbstractThe mixing behavior of a two-channel micromixer with a circular mixing chamber at four different chamber depths and six different flow rates had been investigated. Experiments were implemented with the mixings of two fluids. An image inspection method using the variance of the image gray level contrast as the measurement parameter to determine the mixing efficiency distribution in these mixers. The steady, three-dimensional and laminar flow fields inside the micromixers were also simulated numerically with a finite volume discretization. Through the numerical integration over the chamber depth, the three-dimensional numerical prediction could be compressed into a two-dimensional result, which could be directly used to compare with the experimental measurements. Experimental results show that the measured mixing efficiency is raised with the increase of chamber depth. The numerical prediction of mixing efficiency agreed qualitatively with those obtained from the experimental measurements, while the ratio of the depth to diameter of the mixing chamber is big enough to eliminate the viscosity effect.

Mixing Process in T-Shaped Micro-Mixers With Chaotic Advection: A Numerical Approach

2010 ◽  
Author(s):  
J. Esmaeelpanah ◽  
S. A. Kazemi ◽  
M. Passandideh-Fard
Keyword(s):  
Cross Sections ◽  
Control Volume ◽  
Numerical Approach ◽  
Chaotic Advection ◽  
Mixing Efficiency ◽  
Mixing Length ◽  
Mixing Process ◽  
Governing Equations ◽  
Slip Effects ◽  
Micro Mixer

In this paper, a transient numerical model is presented to investigate the mixing phenomena in passive T-shaped barrier embedded micro-mixer (BEM) with rectangular cross-sections. The simulations are performed for two non-reactive miscible gases (i.e. oxygen and methanol). The compressibility and slip effects of the flow in the micro-channel are neglected. The model presented in this paper is used to numerically solve physical governing equations namely the continuity, momentum and specious transport equations. The equations are discritized using control volume numerical techniques. The distribution of the specious concentration within the domain is calculated. The Intensity factor is used as a criterion for mixing length. Also, the effects of the baffles’ height and span on mixing efficiency and reducing the mixing length are studied. Having baffles in the channel can substantially decrease the mixing length.

Flow Mechanism of a Novel Active Micro-Rotor Mixer

2012 ◽  
Vol 488-489 ◽  
pp. 1177-1183
Author(s):  
Y.C. Liou ◽  
J.M. Miao ◽  
T.L. Liu ◽  
S.J. Cheng
Keyword(s):  
Reynolds Number ◽  
Vortex Flow ◽  
Pure Water ◽  
Inertial Force ◽  
Flow Patterns ◽  
Mixing Efficiency ◽  
Working Fluids ◽  
Rotating Speed ◽  
Mixing Chamber ◽  
Micro Mixer

The purpose of this study is to investigate the complex vortex flow patterns within a novel active micro-rotor mixer under various Reynolds numbers and rotating speeds by employing of CFD technique. The concept of present micro-rotor mixer is inspired from the Wankel-type combustor which is widely used in the power machines. The configuration of present micro-mixer is consisted of a rotor with shape of triangle column, a blending chamber and individual inlet and outlet ports. The blending chamber is served as the mixing chamber since the separated three sub-regions will change their volumes as the rotor undergoing the rotating motion with a fixed eccentricity. The dynamic flow patterns and mixing process of two species within the mixing chamber were simulated and visualized with streak lines. The governing equations are unsteady, two-dimensional incompressible Navier-Stokes equation and the two working fluids are pure water and alcohol. The concentration equation for species is also solved to reveal the mass transfer process in various sub-regions then being calculated on the outlet port to evaluate the mixing efficiency. The dynamic mesh technique was applied to re-distribute the computational meshes when the rotor finished a complete rotation cycle. Inspection on the flow developing stages within the mixing chamber over one complete cycle, it seems that multi-vortex flow field was generated due to the interaction of the shear force from the rotor, viscous force and inertial force of working fluids. The Coanda flow appeared in some conditions. When the Reynolds number is below of 10, the rotating speed of rotor has less influence on the mixing efficiency. An obvious enhancement in the mixing efficiency can be found in cases of the rotating speed of rotor changed from 30 rpm to 150 rpm when the Reynolds number in range of 25 to 100. Generally, the maximum mixing efficiency of 85% can be achieved for 1<Re<100 which demonstrated that present design was effective for μ-TAS.

Enhancement of Mixing in a Micro TAS by Micro-Bubble Emission Boiling

2007 ◽  
Author(s):  
H. Kato ◽  
T. Kimura ◽  
K. Yamazaki ◽  
M. Yamaguchi
Keyword(s):  
Heat Flux ◽  
Nucleate Boiling ◽  
Mixing Efficiency ◽  
Sectional Area ◽  
Cross Sectional ◽  
Maximum Heat ◽  
Two Fluids ◽  
Maximum Heat Flux ◽  
Mixing Chamber ◽  
Micro Bubble

The mixing of two fluids is important in enhancing chemical reactions in a micro TAS. Some devices or methods are needed to enhance the mixing, because the Reynolds number is very low, on the order of 1. In the present research, we studied the possibility of using micro-bubble emission boiling. A heater made of a platinum wire of 30 micrometer was installed in a Y-shaped micro-channel whose cross sectional area was 2 mm × 0.5 mm. The heater was directly powered by electric current up to 1.5 A. The maximum heat flux was 7.47 MW/m2, which was well above the burnout heat flux. The subcool was 80 degrees and the velocity of fluid (colored water) was changed from 0.5 to 2.0 mm/s. When micro-bubble emission boiling occurred, the mixing was improved drastically. The mixing efficiency reached above 90% at v = 2.0 mm/s and q = 7.47MW/m2. In contrast, the mixing efficiency was poor in the case of normal nucleate boiling. The effect of the mixing chamber was also examined.

DYNAMICS OF MIXING PROCESSES IN THE MICRO-MIXER WITH CURVED BLUFF-BODY STRUCTURE UNDER EXTERNAL EXCITATION

2009 ◽  
Vol 23 (03) ◽  
pp. 401-404
Author(s):  
MUH-RONG WANG ◽  
YANG-SHENG HUANG
Keyword(s):  
High Speed ◽  
Bluff Body ◽  
Excitation Frequency ◽  
Mixing Efficiency ◽  
Body Structure ◽  
External Excitation ◽  
Mixing Processes ◽  
Mixing Performance ◽  
Mixing Chamber ◽  
Micro Mixer

This paper investigates the effects of external excitation on the mixing performance of the micromixer with curved bluff-body structure. The micromixer was fabricated by the MEMS process of polydimethylsiloxane (PDMS). The mixing process and mixing efficiency were evaluated with a high speed camera. Results showed that the finger-spiked type flow patterns were generated in the mixing chamber under an excitation frequency of 5Hz. It turns out that the mixing efficiency as high as 85.6% is achieved at Re =0.25 with a single bluff-body structure. It demonstrates that the new design can be used to achieve complete mixing within ultra short length at mciroscale.

Numerical Simulation of Start-Up Jets in a Mixing Chamber

2010 ◽  
Author(s):  
Chenzhou Lian ◽  
Dmytro M. Voytovych ◽  
Guoping Xia ◽  
Charles L. Merkle
Keyword(s):  
Transient Flow ◽  
Three Dimensional ◽  
Cost Effective ◽  
Grid Refinement ◽  
Mixing Process ◽  
Quantitative Estimates ◽  
Start Up ◽  
Mixing Chamber ◽  
Parametric Analyses ◽  
Transient Mixing

Numerical simulations of a transient flow of helium injected into an established background flow of nitrogen were carried out to identify the dominant features of the transient mixing process between these two dissimilar gases. The geometry of interest is composed of two helium slots on either side of a central nitrogen channel feeding into a ‘two-dimensional’ mixing chamber. Simulations were accomplished on both two- and three-dimensional grids using an unsteady DES approach. Results are compared with experimental measurements of species distributions. Unsteady 2-D solutions give a reasonable qualitative picture of the transient mixing process in the middle of the chamber and enable cost-effective parametric analyses and grid refinement studies. The 2-D solutions also provide quantitative estimates of representative characteristic times to guide the 3-D calculations. The 3-D solutions give a reasonable approximation to span-wise events.

A Planar Labyrinth Micromixer

2010 ◽  
Author(s):  
Jeremy T. Cogswell ◽  
Peng Li ◽  
Mohammad Faghri
Keyword(s):  
Soft Lithography ◽  
Lab On A Chip ◽  
Fluorescein Isothiocyanate ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Mixing Length ◽  
Two Fluids ◽  
Curved Channels ◽  
Passive Mixing ◽  
Important Challenge

Rapid mixing of two fluids in microchannels has posed an important challenge to the development of many integrated lab-on-a-chip systems. In this paper, we present a planar labyrinth micromixer (PLM) to achieve rapid and passive mixing by taking advantage of a synergistic combination of the Dean vortices in curved channels, a series of perturbation to the fluids from the sharp turns, and an expansion and contraction of the flow field via a circular chamber. The PLM is constructed in a single soft lithography step and the labyrinth has a footprint of 7.32 mm × 7.32 mm. Experiments using fluorescein isothiocyanate solutions and deionized water demonstrate that the design achieves fast and uniform mixing within 9.8 s to 32 ms for Reynolds numbers between 2.5 and 30. Compared to the mixing in the prevalent serpentine design, our design results in 38% and 79% improvements on the mixing efficiency at Re = 5 and Re = 30 respectively. An inverse relationship between mixing length and mass transfer Pe´clet number (Pe) is observed, which is superior to the logarithmic dependence of mixing length on Pe in chaotic mixers. Having a simple planar structure, the PLM can be easily integrated into lab-on-a-chip devices where passive mixing is needed.

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.

Numerical Simulation on Flow Structure of a Steam-Jet Pump Influenced by Primary Nozzle Geometries

2011 ◽  
Vol 130-134 ◽  
pp. 1703-1707 ◽  
Author(s):  
Xiao Chun Dai ◽  
Jian Huo
Keyword(s):  
Fluid Dynamics ◽  
Flow Structure ◽  
Mixing Process ◽  
Nozzle Outlet ◽  
Jet Pump ◽  
Entrainment Ratio ◽  
Great Loss ◽  
Mixing Chamber ◽  
Throat Diameter ◽  
Nozzle Geometries

The aim of the paper is to reveal the flow structure and the mixing process of a steam-jet pump by using a computational fluid dynamics code FLUENT. Discusses the effect on a steam-jet pump’s entrainment ratio when the throat diameter of the primary nozzle as well as the outlet diameter of the primary nozzle is varied. Analyzes the position of shock wave which will bring the steam-jet pump’s performance a great loss. The performances of a steam-jet pump are studied by changing back pressures while the distance between primary nozzle outlet and mixing chamber inlet (DPM) is varied. The entrainment ratios of a steam-jet pump with different values of DPM and different back pressures are calculated.

scholarly journals Large-Scale Flow in Micro Electrokinetic Turbulent Mixer

Micromachines ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 813 ◽  
Author(s):  
Keyi Nan ◽  
Zhongyan Hu ◽  
Wei Zhao ◽  
Kaige Wang ◽  
Jintao Bai ◽  
...  
Keyword(s):  
Flow Field ◽  
Electric Conductivity ◽  
Large Scale ◽  
Three Dimensional ◽  
Mixing Process ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
Two Fluids ◽  
Large Scale Flow ◽  
Particle Imaging

In the present work, we studied the three-dimensional (3D) mean flow field in a micro electrokinetic (μEK) turbulence based micromixer by micro particle imaging velocimetry (μPIV) with stereoscopic method. A large-scale solenoid-type 3D mean flow field has been observed. The extraordinarily fast mixing process of the μEK turbulent mixer can be primarily attributed to two steps. First, under the strong velocity fluctuations generated by μEK mechanism, the two fluids with different conductivity are highly mixed near the entrance, primarily at the low electric conductivity sides and bias to the bottom wall. Then, the well-mixed fluid in the local region convects to the rest regions of the micromixer by the large-scale solenoid-type 3D mean flow. The mechanism of the large-scale 3D mean flow could be attributed to the unbalanced electroosmotic flows (EOFs) due to the high and low electric conductivity on both the bottom and top surface.

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