Mixing Performance of Different Serpentine Microchannels

2007 ◽  
Author(s):  
C. Nonino ◽  
S. Savino ◽  
S. Del Giudice
Keyword(s):  
Cross Section ◽  
Molecular Diffusion ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Channel Length ◽  
Mixing Enhancement ◽  
Finite Element Code ◽  
Mixing Performance ◽  
Pure Diffusion ◽  
Model Equations

The results of a comparative numerical study aimed at assessing the mixing performance of planar zig-zag, curvilinear and square-wave microchannels of square cross-section is presented in the paper. To evaluate the mixing enhancement characteristics of each geometry, suitable mixing indices are computed at different axial locations of a single repetitive module of each microchannel when this is fed with two equal streams of fluid having the same thermophysical properties, but different solute concentrations. To separate the effects of the geometry from those of molecular diffusion, entrance flow and channel length, the mixing by pure diffusion in straight microchannels of the same length is also evaluated for comparison. Reynolds numbers in the range from 5 to 150 are considered, while the Pe´clet number is held constant and equal to 2500. All the numerical simulations are carried out using an in-house finite element code for the solution of all model equations.

scholarly journals Effects of Channel Wall Twisting on the Mixing in a T-Shaped Micro-Channel

2019 ◽  
Author(s):  
Dong Jin Kang
Keyword(s):  
Reynolds Number ◽  
Cross Section ◽  
Channel Wall ◽  
Numerical Study ◽  
Twist Angle ◽  
Mixing Enhancement ◽  
Micro Channel ◽  
Number Range ◽  
Mixing Performance ◽  
Two Fluids

A new design scheme is proposed for twisting the walls of a microchannel, and its performance is demonstrated numerically. The numerical study was carried out for a T-shaped microchannel with twist angles in the range of 0 to 34π. The Reynolds number range was 0.15 to 6. The T-shaped microchannel consists of two inlet branches and an outlet branch. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the twisting scheme is an effective way to enhance the mixing in a T-shaped microchannel. The mixing enhancement is realized by the swirling of two fluids in the cross section and is more prominent as the Reynolds number decreases. The twist angle was optimized to maximize the DOM, which increases with the length of the outlet branch. The twist angle was also optimized in terms of the relative mixing. The two optimum twisting angles are generally not coincident. The optimum twist angle shows a dependence on the length of the outlet branch but it is not affected much by the Reynolds number.

scholarly journals Effects of Channel Wall Twisting on the Mixing in a T-Shaped Micro-Channel

Micromachines ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 26 ◽  
Author(s):  
Dong Jin Kang
Keyword(s):  
Reynolds Number ◽  
Cross Section ◽  
Channel Wall ◽  
Numerical Study ◽  
Twist Angle ◽  
Mixing Enhancement ◽  
Micro Channel ◽  
Number Range ◽  
Mixing Performance ◽  
Two Fluids

A new design scheme is proposed for twisting the walls of a microchannel, and its performance is demonstrated numerically. The numerical study was carried out for a T-shaped microchannel with twist angles in the range of 0 to 34π. The Reynolds number range was 0.15 to 6. The T-shaped microchannel consists of two inlet branches and an outlet branch. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the twisting scheme is an effective way to enhance the mixing in a T-shaped microchannel. The mixing enhancement is realized by the swirling of two fluids in the cross section and is more prominent as the Reynolds number decreases. The twist angle was optimized to maximize the degree of mixing (DOM), which increases with the length of the outlet branch. The twist angle was also optimized in terms of the relative mixing cost (MC). The two optimum twisting angles are generally not coincident. The optimum twist angle shows a dependence on the length of the outlet branch but it is not affected much by the Reynolds number.

scholarly journals Mixing Performance of a Cross-Channel Split-and-Recombine Micro-Mixer Combined with Mixing Cell

Micromachines ◽  
2020 ◽  
Vol 11 (7) ◽  
pp. 685
Author(s):  
Makhsuda Juraeva ◽  
Dong Jin Kang
Keyword(s):  
Molecular Diffusion ◽  
Numerical Study ◽  
Volume Flow Rate ◽  
Volume Flow ◽  
Mixing Enhancement ◽  
Mixing Performance ◽  
Two Fluids ◽  
Dean Vortex ◽  
Wide Range ◽  
Micro Mixer

A new cross-channel split-and-recombine (CC-SAR) micro-mixer was proposed, and its performance was demonstrated numerically. A numerical study was carried out over a wide range of volume flow rates from 3.1 μL/min to 826.8 μL/min. The corresponding Reynolds number ranges from 0.3 to 80. The present micro-mixer consists of four mixing units. Each mixing unit is constructed by combining one split-and-recombine (SAR) unit with a mixing cell. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the present micro-mixer performs better than other micro-mixers based on SARs over a wide range of volume flow rate. The mixing enhancement is realized by a particular motion of vortex flow: the Dean vortex in the circular sub-channel and another vortex inside the mixing cell. The two vortex flows are generated on the different planes perpendicular to each other. They cause the two fluids to change their relative position as the fluids flow into the circular sub-channel of the SAR, eventually promoting violent mixing. High vorticity in the mixing cell elongates the flow interface between two fluids, and promotes mixing in the flow regime of molecular diffusion dominance.

scholarly journals Numerical and Experimental Study of Cross-Sectional Effects on the Mixing Performance of the Spiral Microfluidics

Micromachines ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1470
Author(s):  
Omid Rouhi ◽  
Sajad Razavi Bazaz ◽  
Hamid Niazmand ◽  
Fateme Mirakhorli ◽  
Sima Mas-hafi ◽  
...  
Keyword(s):  
Cross Sections ◽  
Numerical Study ◽  
Large Angle ◽  
Element Model ◽  
Channel Length ◽  
Cross Sectional ◽  
Flow Rates ◽  
Lab On Chip ◽  
Mixing Performance ◽  
Dean Flow

Mixing at the microscale is of great importance for various applications ranging from biological and chemical synthesis to drug delivery. Among the numerous types of micromixers that have been developed, planar passive spiral micromixers have gained considerable interest due to their ease of fabrication and integration into complex miniaturized systems. However, less attention has been paid to non-planar spiral micromixers with various cross-sections and the effects of these cross-sections on the total performance of the micromixer. Here, mixing performance in a spiral micromixer with different channel cross-sections is evaluated experimentally and numerically in the Re range of 0.001 to 50. The accuracy of the 3D-finite element model was first verified at different flow rates by tracking the mixing index across the loops, which were directly proportional to the spiral radius and were hence also proportional to the Dean flow. It is shown that higher flow rates induce stronger vortices compared to lower flow rates; thus, fewer loops are required for efficient mixing. The numerical study revealed that a large-angle outward trapezoidal cross-section provides the highest mixing performance, reaching efficiencies of up to 95%. Moreover, the velocity/vorticity along the channel length was analyzed and discussed to evaluate channel mixing performance. A relatively low pressure drop (<130 kPa) makes these passive spiral micromixers ideal candidates for various lab-on-chip applications.

Numerical Study on Mixing of Two Fluids With Modified Tesla Structure

2009 ◽  
Author(s):  
Shakhawat Hossain ◽  
Mubashshir Ahmad Ansari ◽  
Afzal Husain ◽  
Kwang-Yong Kim
Keyword(s):  
Vortical Structure ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
The Other ◽  
Channel Width ◽  
Geometrical Parameters ◽  
Fluid Stream ◽  
Mixing Performance ◽  
Two Fluids ◽  
Wide Range

In this study, a parametric investigation on mixing of two fluids in a modified Tesla microchannel, has been preformed. Modified Tesla micromixer applies both flow separation and vortices string principles to enhance the mixing. The fluid stream splits into two sub-streams and one of them mixes with the other again at the exit of the Tesla unit. Analyses of mixing and flow field have been carried out for a wide range of Reynolds number from 0.05 to 40. Mixing performance and pressure drop characteristics with two geometrical parameters, i.e, ratio of the diffuser gap to channel width (h/w) and ratio of the curved gap to the channel width (s/w), have been analyzed at six different Reynolds numbers. The vortical structure of the flow has been analyzed to explain mixing performance. The sensitivity analysis reveals that mixing is more sensitive s/w, than the h/w.

scholarly journals Numerical Investigation of Liquid–Liquid Mixing in Modified T Mixer with 3D Obstacles

2021 ◽  
pp. 25-32
Author(s):  
Md. Readul Mahmud
Keyword(s):  
Numerical Investigation ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Channel Length ◽  
Navier Stokes ◽  
Mixing Efficiency ◽  
Mixing Performance ◽  
Wide Range

The fluids inside passive micromixers are laminar in nature and mixing depends primarily on diffusion. Hence mixing efficiency is generally low, and requires a long channel length and longtime compare to active mixers. Various designs of complex channel structures with/without obstacles and three-dimensional geometries have been investigated in the past to obtain an efficient mixing in passive mixers. This work presents a design of a modified T mixer. To enhance the mixing performance, circular and hexagonal obstacles are introduced inside the modified T mixer. Numerical investigation on mixing and flow characteristics in microchannels is carried out using the computational fluid dynamics (CFD) software ANSYS 15. Mixing in the channels has been analyzed by using Navier–Stokes equations with water-water for a wide range of the Reynolds numbers from 1 to 500. The results show that the modified T mixer with circular obstacles has far better mixing performance than the modified T mixer without obstacles. The reason is that fluids' path length becomes longer due to the presence of obstacles which gives fluids more time to diffuse. For all cases, the modified T mixer with circular obstacle yields the best mixing efficiency (more than 60%) at all examined Reynolds numbers. It is also clear that efficiency increase with axial length. Efficiency can be simply improved by adding extra mixing units to provide adequate mixing. The value of the pressure drop is the lowest for the modified T mixer because there is no obstacle inside the channel. Modified T mixer and modified T mixer with circular obstacle have the lowest and highest mixing cost, respectively. Therefore, the current design of modified T with circular obstacles can act as an effective and simple passive mixing device for various micromixing applications.

scholarly journals Mixing Performance of a Passive Micro-Mixer with Mixing Units Stacked in Cross Flow Direction

Micromachines ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1530
Author(s):  
Makhsuda Juraeva ◽  
Dong-Jin Kang
Keyword(s):  
Numerical Study ◽  
Volume Flow Rate ◽  
Flow Direction ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
High Concentration ◽  
Mixing Performance ◽  
Wall Impingement ◽  
The Cross ◽  
Micro Mixer

A new passive micro-mixer with mixing units stacked in the cross flow direction was proposed, and its performance was evaluated numerically. The present micro-mixer consisted of eight mixing units. Each mixing unit had four baffles, and they were arranged alternatively in the cross flow and transverse direction. The mixing units were stacked in four different ways: one step, two step, four step, and eight step stacking. A numerical study was carried out for the Reynolds numbers from 0.5 to 50. The corresponding volume flow rate ranged from 6.33 μL/min to 633 μL/min. The mixing performance was analyzed in terms of the degree of mixing (DOM) and relative mixing energy cost (MEC). The numerical results showed a noticeable enhancement of the mixing performance compared with other micromixers. The mixing enhancement was achieved by two flow characteristics: baffle wall impingement by a stream of high concentration and swirl motion within the mixing unit. The baffle wall impingement by a stream of high concentration was observed throughout all Reynolds numbers. The swirl motion inside the mixing unit was observed in the cross flow direction, and became significant as the Reynolds number increased to larger than about five. The eight step stacking showed the best performance for Reynolds numbers larger than about two, while the two step stacking was better for Reynolds numbers less than about two.

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.

scholarly journals Mixing Performance of a Cost-effective Split-and-Recombine 3D Micromixer Fabricated by Xurographic Method

Micromachines ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 786 ◽  
Author(s):  
Ramezan Ali Taheri ◽  
Vahabodin Goodarzi ◽  
Abdollah Allahverdi
Keyword(s):  
High Efficiency ◽  
Molecular Diffusion ◽  
Low Cost ◽  
Three Dimensional ◽  
Cost Effective ◽  
Reynolds Numbers ◽  
Mixing Performance ◽  
Wide Range ◽  
Fluid Layers ◽  
Passive Micromixer

This paper presents experimental and numerical investigations of a novel passive micromixer based on the lamination of fluid layers. Lamination-based mixers benefit from increasing the contact surface between two fluid phases by enhancing molecular diffusion to achieve a faster mixing. Novel three-dimensional split and recombine (SAR) structures are proposed to generate fluid laminations. Numerical simulations were conducted to model the mixer performance. Furthermore, experiments were conducted using dyes to observe fluid laminations and evaluate the proposed mixer’s characteristics. Mixing quality was experimentally obtained by means of image-based mixing index (MI) measurement. The multi-layer device was fabricated utilizing the Xurography method, which is a simple and low-cost method to fabricate 3D microfluidic devices. Mixing indexes of 96% and 90% were obtained at Reynolds numbers of 0.1 and 1, respectively. Moreover, the device had an MI value of 67% at a Reynolds number of 10 (flow rate of 116 µL/min for each inlet). The proposed micromixer, with its novel design and fabrication method, is expected to benefit a wide range of lab-on-a-chip applications, due to its high efficiency, low cost, high throughput and ease of fabrication.

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.

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