scholarly journals Optimal Combination of Mixing Units Using the Design of Experiments Method

Micromachines ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 985
Author(s):  
Makhsuda Juraeva ◽  
Dong-Jin Kang
Keyword(s):  
Statistical Significance ◽  
Reynolds Numbers ◽  
Optimal Combination ◽  
Mixing Performance ◽  
Mixing Energy ◽  
Combination Unit ◽  
Combination Scheme ◽  
Wide Range ◽  
Passive Micromixer ◽  
Simulation Results

A passive micromixer was designed by combining two mixing units: the cross-channel split and recombined (CC-SAR) and a mixing cell with baffles (MC-B). The passive micromixer was comprised of eight mixing slots that corresponded to four combination units; two mixing slots were grouped as one combination unit. The combination of the two mixing units was based on four combination schemes: (A) first mixing unit, (B) first combination unit, (C) first combination module, and (D) second combination module. The statistical significance of the four combination schemes was analyzed using analysis of variance (ANOVA) in terms of the degree of mixing (DOM) and mixing energy cost (MEC). The DOM and MEC were simulated numerically for three Reynolds numbers (Re = 0.5, 2, and 50), representing three mixing regimes. The combination scheme (B), using different mixing units in the first two mixing slots, was significant for Re = 2 and 50. The four combination schemes had little effect on the mixing performance of a passive micromixer operating in the mixing regime of molecular dominance. The combination scheme (B) was generalized to arbitrary mixing slots, and its significance was analyzed for Re = 2 and 50. The general combination scheme meant two different mixing units in two consecutive mixing slots. The numerical simulation results showed that the general combination scheme was statistically significant in the first three combination units for Re = 2, and significant in the first two combination units for Re = 50. The combined micromixer based on the general combination scheme throughout the entire micromixer showed the best mixing performance over a wide range of Reynolds numbers, compared to other micromixers that did not adopt completely the general combination scheme. The most significant enhancement due to the general combination scheme was observed in the transition mixing scheme and was negligible in the molecular dominance scheme. The combination order was less significant after three combination units.

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.

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.

Analysis of a Novel Y-Y Micromixer for Mixing at a Wide Range of Reynolds Numbers

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Vladimir Viktorov ◽  
Carmen Visconte ◽  
Md Readul Mahmud
Keyword(s):  
Three Dimensional ◽  
Interfacial Area ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Change Of Direction ◽  
Analysis Technique ◽  
Wide Range ◽  
Passive Micromixer ◽  
In Series ◽  
Flow Through

A novel passive micromixer, denoted as the Y-Y mixer, based on split-and-recombine (SAR) principle is proposed and studied both experimentally and numerically over Reynolds numbers ranging from 1 to 100. Two species are supplied to a prototype via a Y inlet, and flow through four identical elements repeated in series; the width of the mixing channel varies from 0.4 to 0.6 mm, while depth is 0.4 mm. An image analysis technique was used to evaluate mixture homogeneity at four target areas along the mixer. Numerical simulations were found to be a useful support for observing the complex three-dimensional flow inside the channels. Comparison with a known mixer, the tear-drop one, based on the same SAR principle, was also performed, to have a point of reference for evaluating performances. A good agreement was found between numerical and experimental results. Over the examined range of Reynolds numbers Re, the Y-Y micromixer showed at its exit an almost flat mixing characteristic, with a mixing efficiency higher than 0.9; conversely, the tear-drop mixer showed a relevant decrease of efficiency at the midrange. The good performance of the Y-Y micromixer is due to the three-dimensional 90 deg change of direction that occurs in its channel geometry, which causes a fluid swirling already at the midrange of Reynolds numbers. Consequently, the fluid path is lengthened and the interfacial area of species is increased, compensating for the residence time reduction.

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.

A Novel Passive Micromixer Based on Asymmetric Split-and-Recombine With Fan-Shaped Cavity

2011 ◽  
Author(s):  
Guodong Xia ◽  
Jian Li ◽  
Hongjie Wu ◽  
Mingzheng Zhou ◽  
Haiyan Wang
Keyword(s):  
Stokes Equations ◽  
Vertical Plane ◽  
Reynolds Numbers ◽  
Viscous Effects ◽  
Mixing Index ◽  
Cross Sectional ◽  
Dean Vortices ◽  
Wide Range ◽  
Cavity Structure ◽  
Passive Micromixer

A novel passive micromixer with fan-shaped cavity based on the principle of flow planar asymmetric split-and-recombine (P-ASAR) and focusing/diverging is designed. The micromixer consists of two split sub-channels with unequal widths and one fan-shaped cavity structure on the major sub-channel which are similar to a diamond ring structure. In order to yield optimum mixing effect, different parameters of geometry structure under a wide range of Reynolds numbers (1–80) have been investigated by numerical simulation with three-dimensional Navier-Stokes equations. The steady laminar flow was solved by using a finite-volume method and SIMPLE algorithm. Enhanced micromixing is achieved by utilizing a synergistic combination of unbalanced inertial collision, Dean vortices and expansion vortices. As a result of interplay between inertial, centrifugal and viscous effects, Dean vortices arise in the vertical plane of curved channel. Expansion vortices appear in the horizontal plane due to an abrupt increase of the cross-sectional area. The mixing index is used to evaluate the degree of mixing. Our studies show that vortices are observed in the channels at high Reynolds numbers. The geometry parameters of fan-shaped cavity structure affect the mixing index of micromixer. When the ratio of the widths of the major sub-channel and fan-shaped cavity channel is 1/3, the mixing index of this type micromixer could reach around 75% at Reynolds numbers larger than 60. The relation between mixing intensity and pump power consumption has been analyzed at a wide range of Reynolds numbers simultaneously.

Simulations of Flow and Mass Transfer in a Passive Micromixer

2011 ◽  
Author(s):  
Hamid Farangis Zadeh ◽  
Arash Marahel
Keyword(s):  
Reynolds Number ◽  
Three Dimensional ◽  
Main Idea ◽  
Contact Layer ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Low Reynolds Numbers ◽  
Passive Micromixer ◽  
Simulation Results ◽  
Dimensional Simulation

We present three-dimensional simulation results regarding performance of a novel planar passive micromixer functioning at low Reynolds numbers. A combination of folding and contracting of microchannels is the main idea for designing of an effective, easy-to-produce, and non-expensive micromixer. The simulation results show that, depend on Reynolds number, centrifugal forces can generate different secondary flows and Dean vortices after each bend. Consequently, the thickness and the form of the contact layer between fluids become strongly affected. The simulation process is repeated for different Reynolds numbers from 10 to 100, and we observe that the maximum and minimum mixing efficiencies at the output channel are related to Reynolds number 60 and 80, respectively.

A Micromixer with Two-Layer Crossing Microchannels Based on PMMA Bonding Process

2019 ◽  
Vol 17 (8) ◽  
Author(s):  
Jibo Wang ◽  
Guojun Liu ◽  
Xinbo Li ◽  
Fang He ◽  
Xiang Ma
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Bonding Process ◽  
Parameters Optimization ◽  
Chaotic Advection ◽  
Blue Dye ◽  
Number Range ◽  
Mixing Performance ◽  
Dean Vortices ◽  
Wide Range

AbstractA micromixer with two-layer crossing microchannels based on PMMA bonding process was proposed. The micromixer consists of two-layer crossing microchannels and periodic mixing chambers. The numerical simulation and parameters optimization of the micromixer were carried out in a Reynolds number range of 0.5–100 using CFD software, and the prototype of micromixer was manufactured by PMMA bonding process under certain temperature and pressure condition. The mixing performance of the micromixer was tested and verified by the mixing experiments using red-blue dye. Both the numerical and experimental results confirmed that the micromixer achieves an excellent mixing characteristics over a wide range of Reynolds numbers through generating Dean vortices and chaotic advection. At the same time, the PMMA bonding process proposed in this paper has certain application value and reference significance for expanding the application of three-dimensional flow channels in the field of microfluidics.

Numerical Investigation and Geometric Parameterization of Lamination Inlet of Passive Micromixer

2010 ◽  
Author(s):  
Yanfeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Mixing Length ◽  
Straight Channel ◽  
Interface Area ◽  
Mixing Performance ◽  
Passive Micromixer ◽  
Two Parameters ◽  
Parallel Type

A lamination inlet is proposed and optimized in this paper. The perpendicular incoming fluids are applied instead of parallel type. The total mixing length is fixed at 3.2 mm and the depth of channel is fixed at 0.1 mm. The tested Reynolds number is calculated at the entrance of downstream straight channel. The tested Reynolds numbers range from 5 to 200. The perpendicular incoming type enhances the mass-convection and enlarges the interface area. Two parameters, the radius of holes (R) and the distance between two holes (D1), are selected to achieve the optimization. Numerical simulation is used to estimate the mixing performance and flow characteristics. The results show that the vortices are generated in the microchannel. The interface becomes irregular. In order to evaluate the mixing improvement, the parallel lamination is also simulated. The comparison shows that the perpendicular inlet type has better mixing efficiency than the parallel lamination type. This inlet type could be connected with certain mixing element to achieve the applications in biochemistry.

Analysis of Mixing and Flow Structure in Different Passive Micromixers

2009 ◽  
Author(s):  
Shakhawat Hossain ◽  
Mubashshir Ahmad Ansari ◽  
Kwang-Yong Kim
Keyword(s):  
Pressure Drop ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Channel Height ◽  
Navier Stokes Equations ◽  
Pressure Drops ◽  
Square Wave ◽  
Mixing Performance ◽  
Wide Range

This work presents a numerical investigation on mixing and flow structures in microchannels with different geometries: zig-zag; square-wave; and curved. To conduct the investigation, geometric parameters, such as the area of the cross-section of channel, height of the channel, axial length of the channel, and number of pitches, are kept constant for all three cases. Analyses of mixing and flow fields have been carried out for a wide range 0.267 to 267 of the Reynolds number. Mixing in the channels has been analyzed by using Navier-Stokes equations with two working fluids, water and ethanol. The results show that the square-wave microchannel yields the best mixing performance, and the curved and the zig-zag microchannels show nearly the same performance for most Reynolds numbers. For all three cases, the pressure drop has been calculated for channels with equal streamwise-lengths. The curved channel exhibits the smallest pressure drop among the microchannels, while the pressure drops in the square-wave and zigzag channels are approximately the same.

scholarly journals COVID-19 and Its Symptoms’ Panoply: A Case-Control Study of 919 Suspected Cases in Locked-Down Ovar, Portugal

2021 ◽  
pp. 1-8
Author(s):  
Regina Sá ◽  
Tiago Pinho-Bandeira ◽  
Guilherme Queiroz ◽  
Joana Matos ◽  
João Duarte Ferreira ◽  
...  
Keyword(s):  
Large Scale ◽  
Case Control Study ◽  
Statistical Significance ◽  
Case Control ◽  
Case Definition ◽  
Suspected Case ◽  
Risk Characteristics ◽  
Increased Risk ◽  
Wide Range ◽  
Control Study

<b><i>Background:</i></b> Ovar was the first Portuguese municipality to declare active community transmission of SARS-CoV-2, with total lockdown decreed on March 17, 2020. This context provided conditions for a large-scale testing strategy, allowing a referral system considering other symptoms besides the ones that were part of the case definition (fever, cough, and dyspnea). This study aims to identify other symptoms associated with COVID-19 since it may clarify the pre-test probability of the occurrence of the disease. <b><i>Methods:</i></b> This case-control study uses primary care registers between March 29 and May 10, 2020 in Ovar municipality. Pre-test clinical and exposure-risk characteristics, reported by physicians, were collected through a form, and linked with their laboratory result. <b><i>Results:</i></b> The study population included a total of 919 patients, of whom 226 (24.6%) were COVID-19 cases and 693 were negative for SARS-CoV-2. Only 27.1% of the patients reporting contact with a confirmed or suspected case tested positive. In the multivariate analysis, statistical significance was obtained for headaches (OR 0.558), odynophagia (OR 0.273), anosmia (OR 2.360), and other symptoms (OR 2.157). The interaction of anosmia and odynophagia appeared as possibly relevant with a borderline statistically significant OR of 3.375. <b><i>Conclusion:</i></b> COVID-19 has a wide range of symptoms. Of the myriad described, the present study highlights anosmia itself and calls for additional studies on the interaction between anosmia and odynophagia. Headaches and odynophagia by themselves are not associated with an increased risk for the disease. These findings may help clinicians in deciding when to test, especially when other diseases with similar symptoms are more prevalent, namely in winter.

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