The Numerical Investigation of an Interdigital Micromixer With the Circular-Sector Obstacles

2009 ◽  
Author(s):  
Yan Feng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Surface Area ◽  
Molecular Diffusion ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Mixing Enhancement ◽  
Mixing Length ◽  
Circular Sector ◽  
Lateral Direction ◽  
Low Reynolds Numbers ◽  
Low Reynolds

In this paper, a passive interdigital micromixer with the circular-sector obstacles is proposed and the mixing performance is estimated by numerical simulation. The tested Reynolds numbers range from 0.01 to 10. Flow recirculation or vortices seems impossible to generate to enhance the mixing at such low Reynolds numbers. Hence, molecular diffusion is the dominant mixing mechanism. Based on the diffusion principle, enlarging the mixing length, reducing the diffusion length and increasing the surface area between species are major methods to obtain mixing enhancement. In order to achieve rapid mixing, shortening the mixing length is necessary. However, the reduced mixing length induces the decreased mixing time which the species take to mix. The circular-section obstacles are placed in the straight microchannels to enlarge the contact surface area between species. The flow path is distorted after passing the obstacles so that the real mixing length increases compared with traditional T-shape micromixers. Furthermore, flow advection takes a part role in mixing since the velocity direction is no longer perpendicular to diffusion direction. Different geometries and layouts of obstacles are analyzed for optimization. The results of optimal design show the worst mixing efficiency, around 50%, occurs at Re = 1. In order to improve the lower limitation of mixing efficiency, the duplicated layouts of obstacles in lateral direction with interdigital inlet are applied to reduce the diffusion path and increase the interface area so that the mixing efficiency could be enhanced. The results show that the mixing efficiency could achieve 85% at Re ≤ 1 with a low pressure drop of 100 Pa. It has the potential to be used in applications with low Reynolds numbers.

Exploiting the Confined Twin-Jet Instability for Micro Mixing Enhancement

2004 ◽  
Author(s):  
Assaf Nahum ◽  
Avraham Seifert
Keyword(s):  
Hydrodynamic Instability ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Mixing Enhancement ◽  
Mean Flow ◽  
Unstable Flow ◽  
Low Reynolds Numbers ◽  
Jet Instability ◽  
Perturbation Frequency ◽  
Computational Fluid Dynamics Cfd

A method for exploiting hydrodynamic instability for enhancement of micro-mixing is proposed, studied numerically and demonstrated experimentally. The confined twin-jet geometry is selected as the baseline unstable flow, since it undergoes a Hopf bifurcation at low Reynolds numbers. It is shown that by adding weak fluidic perturbation to the mean flow, significant amplification of unstable modes results, leading to enhanced mixing in laminar flow. Good agreement was found between Computational Fluid Dynamics (CFD) and experimental results for the critical Re, for which instability sets-in, and its related Struohal number. In order to evaluate mixing efficiency, backward tracing particle was performed using the computed flow field. Mixing is estimated based on particle’s location in time and space. A parametric mixing study was performed and its results are presented and discussed. It is shown that mixing was significantly enhanced when the perturbation frequency was matched with the baseline’s most-unstable Struohal number, even for sub-critical Reynolds number.

scholarly journals Kinematic Measurements of Novel Chaotic Micromixers to Enhance Mixing Performances at Low Reynolds Numbers: Comparative Study

Micromachines ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 364
Author(s):  
Toufik Tayeb Naas ◽  
Shakhawat Hossain ◽  
Muhammad Aslam ◽  
Arifur Rahman ◽  
A. S. M. Hoque ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Comparative Investigation ◽  
Mixing Enhancement ◽  
Passive Mixer ◽  
Low Reynolds Numbers ◽  
Pressure Losses ◽  
Computational Evaluation ◽  
Low Reynolds

In this work, a comparative investigation of chaotic flow behavior inside multi-layer crossing channels was numerically carried out to select suitable micromixers. New micromixers were proposed and compared with an efficient passive mixer called a Two-Layer Crossing Channel Micromixer (TLCCM), which was investigated recently. The computational evaluation was a concern to the mixing enhancement and kinematic measurements, such as vorticity, deformation, stretching, and folding rates for various low Reynolds number regimes. The 3D continuity, momentum, and species transport equations were solved by a Fluent ANSYS CFD code. For various cases of fluid regimes (0.1 to 25 values of Reynolds number), the new configuration displayed a mixing enhancement of 40%–60% relative to that obtained in the older TLCCM in terms of kinematic measurement, which was studied recently. The results revealed that all proposed micromixers have a strong secondary flow, which significantly enhances the fluid kinematic performances at low Reynolds numbers. The visualization of mass fraction and path-lines presents that the TLCCM configuration is inefficient at low Reynolds numbers, while the new designs exhibit rapid mixing with lower pressure losses. Thus, it can be used to enhance the homogenization in several microfluidic systems.

Experimental Investigation of a Scaled-Up Passive Interdigital Micromixer With Circular-Sector Mixing Elements

2011 ◽  
Author(s):  
Kristina Cook ◽  
YanFeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Molecular Diffusion ◽  
Vortex Formation ◽  
Diffusion Path ◽  
Reynolds Numbers ◽  
Channel Length ◽  
Mixing Efficiency ◽  
Circular Sector ◽  
Dean Vortex ◽  
Side Walls ◽  
High Reynolds

Flow patterns and mixing phenomena are investigated qualitatively in a planar passive scaled-up micromixer using flow visualization over 5 ≤ Re ≤ 200. To promote molecular diffusion, the test section utilizes an uneven interdigital inlet which reduces the diffusion path and enhances mixing at the side walls. Five circular sector obstructions located along the channel length serve to divide and recombine the flow, as well as induce Dean vortex formation at high Reynolds numbers. Induced fluorescence is used to provide a quantitative estimate of mixing efficiency at certain Reynolds numbers. A decreasing-increasing trend in mixing efficiency is observed with increasing Reynolds numbers, marking the transition from mass diffusion dominance to mass advection dominance. The design operates well at higher Reynolds numbers, where the dominant mixing mechanism is mass advection.

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.

Analysis of a Vibrating-Beam-Based Micromixer

2007 ◽  
Author(s):  
Hongwei Sun ◽  
Pengtao Wang
Keyword(s):  
Molecular Diffusion ◽  
Reynolds Numbers ◽  
Laminar Flows ◽  
Chaotic Advection ◽  
Mixing Efficiency ◽  
Microfluidic Channels ◽  
Low Reynolds Numbers ◽  
Practical Applications ◽  
Mixer Design ◽  
Beam Movement

The mixing of two or more streams in microscale devices is a slowly molecular diffusion process due to the unique laminar flows, and some ‘turbulence’ based mixing technologies which are effective in macroscales become hard to implement in such small dimensions. The chaotic advection based mixing, depending on the stretching and folding of interface, has been proved to be effective for low Reynolds numbers (Re) and is a very promising technology for micro mixing. We propose a new mixing concept based on a vibrating micro-beam in microfluidic channels to generate chaotic advection to achieve an efficient mixing. The simplicity of the proposed mixer design makes microfabrication process easy for practical applications. The feasibility of the concept is evaluated computationally and moving mesh technique (ALE) is utilized to trace the beam movement. The simulation shows that the mixing quality is determined by parameters such as flow velocities, amplitudes and frequencies of vibrating beam. The Reynolds number (Re) is less than 2.0, Pelect number (Pe) ranges from 5 to 1000, and Strohal number (St) 0.3 to 3.0. It was found that vortex type of flows were generated in microchannel due to the interaction between beam and channel wall. The mixing efficiency with this design is well improved comparing with the flows without beam vibration.

Investigation on the effect of leading edge tubercles of sweptback wing at low reynolds number

2020 ◽  
Vol 21 (6) ◽  
pp. 621
Author(s):  
Veerapathiran Thangaraj Gopinathan ◽  
John Bruce Ralphin Rose ◽  
Mohanram Surya
Keyword(s):  
Leading Edge ◽  
Reynolds Numbers ◽  
Sweep Angle ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Flow Energy ◽  
Airplane Wing ◽  
Low Reynolds ◽  
Naca 0015 ◽  
Wing Performance

Aerodynamic efficiency of an airplane wing can be improved either by increasing its lift generation tendency or by reducing the drag. Recently, Bio-inspired designs have been received greater attention for the geometric modifications of airplane wings. One of the bio-inspired designs contains sinusoidal Humpback Whale (HW) tubercles, i.e., protuberances exist at the wing leading edge (LE). The tubercles have excellent flow control characteristics at low Reynolds numbers. The present work describes about the effect of tubercles on swept back wing performance at various Angle of Attack (AoA). NACA 0015 and NACA 4415 airfoils are used for swept back wing design with sweep angle about 30°. The modified wings (HUMP 0015 A, HUMP 0015 B, HUMP 4415 A, HUMP 4415 B) are designed with two amplitude to wavelength ratios (η) of 0.1 & 0.24 for the performance analysis. It is a novel effort to analyze the tubercle vortices along the span that induce additional flow energy especially, behind the tubercles peak and trough region. Subsequently, Co-efficient of Lift (CL), Co-efficient of Drag (CD) and boundary layer pressure gradients also predicted for modified and baseline (smooth LE) models in the pre & post-stall regimes. It was observed that the tubercles increase the performance of swept back wings by the enhanced CL/CD ratio in the pre-stall AoA region. Interestingly, the flow separation region behind the centerline of tubercles and formation of Laminar Separation Bubbles (LSB) were asymmetric because of the sweep.

Low Reynolds number flow around and heat transfer from a heated circular cylinder

2010 ◽  
Vol 1 (1-2) ◽  
pp. 15-20 ◽  
Author(s):  
B. Bolló
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Reynolds Number Flow ◽  
Two Dimensional Flow ◽  
Number Flow ◽  
Low Reynolds ◽  
Increasing Temperature

Abstract The two-dimensional flow around a stationary heated circular cylinder at low Reynolds numbers of 50 < Re < 210 is investigated numerically using the FLUENT commercial software package. The dimensionless vortex shedding frequency (St) reduces with increasing temperature at a given Reynolds number. The effective temperature concept was used and St-Re data were successfully transformed to the St-Reeff curve. Comparisons include root-mean-square values of the lift coefficient and Nusselt number. The results agree well with available data in the literature.

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