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.

Flow Pulsation and Geometry Effects on Mixing of Two Miscible Fluids in Microchannels

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Houssein Ammar ◽  
Ahmed Ould el Moctar ◽  
Bertrand Garnier ◽  
Hassan Peerhossaini
Keyword(s):  
Reynolds Number ◽  
Residence Time ◽  
Pure Water ◽  
Mixing Efficiency ◽  
Mixing Enhancement ◽  
Flow Pulsation ◽  
Mean Flow ◽  
Mixing Index ◽  
Two Fluids ◽  
Passive Mixing

Many microfluidic applications involve chemical reactions. Most often, the flow is predominantly laminar, and without active or passive mixing enhancement the reaction time can be extremely long compared to the residence time. In this work we demonstrate the merits of the combination of flow pulsation and geometrical characteristics in enhancing mixing efficiency in microchannels. Mixing was studied by introducing a mixing index based on the gray level observed in a heterogeneous flow of pure water and water colored by rhodamine B. The effects of the injection geometry at the microchannel inlet and the use of pulsed flows with average Reynolds numbers between 0.8 and 2 were studied experimentally and numerically. It appeared that the mixing index increases with the nondimensional residence time (τ), which is inversely proportional to the Reynolds number. In addition, we show that the mixing efficiency depends strongly on the geometry of the intersection between the two fluids. Better mixing was achieved with sharp corners (arrowhead and T intersections) in all cases investigated. In pulsed flow, the mixing efficiency is shown to depend strongly on the ratio (β) between the peak amplitude and the mean flow rate. Optimal conditions for mixing in the microchannels are summarized as a function of Reynolds number Re, the ratio β, and the geometries.

scholarly journals A stretchable micromixer with enhanced performance for intermediate Reynolds numbers

2021 ◽  
Author(s):  
Hedieh Fallahi ◽  
Jun Zhang ◽  
Jordan Nicholls ◽  
Pradip Singha ◽  
Nhat-Khuong Nguyen ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Molecular Diffusion ◽  
Inertial Force ◽  
Reynolds Numbers ◽  
Chaotic Advection ◽  
Low Flow ◽  
Viscous Force ◽  
Mixing Efficiency ◽  
Potential Candidate ◽  
Low Reynolds

Abstract Chemical reactions in microscale require good mixing at a relatively low flowrate. However, mixing in microscale faces the major challenge of stable laminar flow associated with the low Reynolds number, the relative ratio between inertial force and viscous force. For low Reynolds numbers of less than unity, mixing occurs due to molecular diffusion. For high Reynolds number of more than several tens, chaotic advection enhances mixing. However, in the intermediate regime, mixing is not efficient. This paper reports a stretchable micromixer with dynamically tuneable channel dimensions. Periodically stretching the device changes the channel geometry and the curvature induced secondary Dean flows. The dynamically evolving secondary and main flows in the mixing channel result in chaotic advection and enhance mixing. The concept was demonstrated in a stretchable micromixer with a serpentine channel. We evaluated the performance of this stretchable micromixer both experimentally and numerically. At the intermediate range of Reynolds numbers from 4 to 17, the periodically stretched micromixer showed a better mixing efficiency than the non-stretched counterpart. Therefore, our stretchable micromixer is a potential candidate for applications where precious reagents need to be mixed at relatively low flow rate conditions.

scholarly journals A stretchable micrometer with enhanced performance for intermediate Reynolds numbers

2021 ◽  
Author(s):  
Hedieh Fallahi ◽  
Jun Zhang ◽  
Jordan Nicholls ◽  
Pradip Singha ◽  
Nhat-Khuong Nguyen ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Molecular Diffusion ◽  
Inertial Force ◽  
Reynolds Numbers ◽  
Chaotic Advection ◽  
Low Flow ◽  
Viscous Force ◽  
Mixing Efficiency ◽  
Potential Candidate ◽  
Low Reynolds

Abstract Chemical reactions in microscale require good mixing at a relatively low flowrate. However, mixing in microscale faces the major challenge of stable laminar flow associated with the low Reynolds number, the relative ratio between inertial force and viscous force. For low Reynolds numbers of less than unity, mixing occurs due to molecular diffusion. For high Reynolds number of more than several tens, chaotic advection enhances mixing. However, in the intermediate regime, mixing is not efficient. This paper reports a stretchable micromixer with dynamically tuneable channel dimensions. Periodically stretching the device changes the channel geometry and the curvature induced secondary Dean flows. The dynamically evolving secondary and main flows in the mixing channel result in chaotic advection and enhance mixing. The concept was demonstrated in a stretchable micromixer with a serpentine channel. We evaluated the performance of this stretchable micromixer both experimentally and numerically. At the intermediate range of Reynolds numbers from 4 to 17, the periodically stretched micromixer showed a better mixing efficiency than the non-stretched counterpart. Therefore, our stretchable micromixer is a potential candidate for applications where precious reagents need to be mixed at relatively low flow rate conditions.

Numerical Analysis on a Passive Chaotic Micromixer with Helical Microchannel

2006 ◽  
Vol 6 (1) ◽  
pp. 190-194 ◽  
Author(s):  
Ruijin Wang ◽  
Jianzhong Lin
Keyword(s):  
Reynolds Number ◽  
Numerical Analysis ◽  
High Reynolds Number ◽  
Mixing Efficiency ◽  
Micro Channel ◽  
High Reynolds ◽  
Helical Microchannel ◽  
Micro Mixer

In order to improve the mixing efficiency, the diffusion and mixing of species in the helical micro-mixer are simulated numerically. The results show that the mixing efficiency in the helical micro-mixer is much higher than that in the straight micro-channel and obviously higher than that in the serpentine micro-channel when Reynolds number is low. At high Reynolds number, even though the mixing efficiency in the helical micro-mixer is still much higher than that in the straight micro-channel, no obvious difference of mixing efficiency in the helical micro-mixer and serpentine micro-channel is found. The conclusions are helpful to optimize the structure of the micro-mixer.

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.

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.

scholarly journals Simulation approach on turbulent thermal performance factor of Al2O3-Cu/water hybrid nanofluid in circular and non-circular ducts

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Ing Jiat Kendrick Wong ◽  
Ngieng Tze Angnes Tiong
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Thermal Performance ◽  
Heat Transfer Performance ◽  
Pure Water ◽  
Hybrid Nanofluid ◽  
Performance Factor ◽  
Thermal Performance Factor ◽  
The Heat Transfer Coefficient

AbstractThis paper presents the numerical study of thermal performance factor of Al2O3-Cu/water hybrid nanofluid in circular and non-circular ducts (square and rectangular). Turbulent regime is studied with the Reynolds number ranges from 10000 to 100000. The heat transfer performance and flow behaviour of hybrid nanofluid are investigated, considering the nanofluid volume concentration between 0.1 and 2%. The thermal performance factor of hybrid nanofluid is evaluated in terms of performance evaluation criteria (PEC). This present numerical results are successfully validated with the data from the literature. The results indicate that the heat transfer coefficient and Nusselt number of Al2O3-Cu/water hybrid nanofluid are higher than those of Al2O3/water nanofluid and pure water. However, this heat transfer enhancement is achieved at the expense of an increased pressure drop. The heat transfer coefficient of 2% hybrid nanofluid is approximately 58.6% larger than the value of pure water at the Reynolds number of 10000. For the same concentration and Reynolds number, the pressure drop of hybrid nanofluid is 4.79 times higher than the pressure drop of water. The heat transfer performance is the best in the circular pipe compared to the non-circular ducts, but its pressure drop increment is also the largest. The hybrid nanofluid helps to improve the problem of low heat transfer characteristic in the non-circular ducts. In overall, the hybrid nanofluid flow in circular and non-circular ducts are reported to possess better thermal performance factor than that of water. The maximum attainable PEC is obtained by 2% hybrid nanofluid in the square duct at the Reynolds Number of 60000. This study can help to determine which geometry is efficient for the heat transfer application of hybrid nanofluid.

EXPERIMENTAL STUDY ON THERMAL TRANSPORT PHENOMENON OF NANOFLUIDS AS WORKING FLUID IN HEAT EXCHANGER

2014 ◽  
Vol 22 (01) ◽  
pp. 1450005 ◽  
Author(s):  
SHUICHI TORII
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Performance ◽  
Pure Water ◽  
Horizontal Tube ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
Transfer Performance ◽  
Nanoparticles Concentration ◽  
Transfer Behavior

This paper aims to study the convective heat transfer behavior of aqueous suspensions of nanoparticles flowing through a horizontal tube heated under constant heat flux condition. Consideration is given to the effects of particle concentration and Reynolds number on heat transfer enhancement and the possibility of nanofluids as the working fluid in various heat exchangers. It is found that (i) significant enhancement of heat transfer performance due to suspension of nanoparticles in the circular tube flow is observed in comparison with pure water as the working fluid, (ii) enhancement is intensified with an increase in the Reynolds number and the nanoparticles concentration, and (iii) substantial amplification of heat transfer performance is not attributed purely to the enhancement of thermal conductivity due to suspension of nanoparticles.

An Enhanced One-Layer Passive Microfluidic Mixer With an Optimized Lateral Structure With the Dean Effect

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Teng Zhou ◽  
Yifan Xu ◽  
Zhenyu Liu ◽  
Sang Woo Joo
Keyword(s):  
Reynolds Number ◽  
Topology Optimization ◽  
Optimization Method ◽  
Mixing Efficiency ◽  
Boolean Operation ◽  
Microfluidic Mixer ◽  
Wide Range ◽  
The One ◽  
Lateral Structure ◽  
Topology Optimization Method

Topology optimization method is applied to a contraction–expansion structure, based on which a simplified lateral flow structure is generated using the Boolean operation. A new one-layer mixer is then designed by sequentially connecting this lateral structure and bent channels. The mixing efficiency is further optimized via iterations on key geometric parameters associated with the one-layer mixer designed. Numerical results indicate that the optimized mixer has better mixing efficiency than the conventional contraction–expansion mixer for a wide range of the Reynolds number.

Quantitative Experimental Study of SiO2-Water Nanofluids on Backward-Facing Step Flow under Low Reynolds Number

2018 ◽  
Vol 916 ◽  
pp. 221-225
Author(s):  
Ji Zu Lv ◽  
Liang Yu Li ◽  
Cheng Zhi Hu ◽  
Min Li Bai ◽  
Sheng Nan Chang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Reynolds Number ◽  
Volume Fraction ◽  
Pure Water ◽  
Experimental Studies ◽  
Flow Characteristics ◽  
Thermal Engineering ◽  
Heat Transfer Medium ◽  
Step Flow

Nanofluids is an innovative study of nanotechnology applied to the traditional field of thermal engineering. It refers to the metal or non-metallic nanopowder was dispersed into water, alcohol, oil and other traditional heat transfer medium, to prepared as a new heat transfer medium with high thermal conductivity. The role of nanofluids in strengthening heat transfer has been confirmed by a large number of experimental studies. Its heat transfer mechanism is mainly divided into two aspects. On the one hand, the addition of nanoparticles enhances the thermal conductivity. On the other hand, due to the interaction between the nanoparticles and base fluid causing the changes in the flow characteristics, which is also the main factor affecting the heat transfer of nanofluids. Therefore, a intensive study on the flow characteristics of nanofluids will make the study of heat transfer more meaningful. In this experiment, the flow characteristics of SiO2-water nanofluids in two-dimensional backward step flow are quantitatively studied by PIV. The results show that under the same Reynolds number, the turbulence of nanofluids is larger than that of pure water. With the increase of nanofluids volume fraction, the flow characteristics are constantly changing. The quantitative analysis proved that the nanofluids disturbance was enhanced compared with the base liquid, which resulting in the heat transfer enhancement.

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