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14243 KiB

Open AccessArticle

Comparative Analysis of Passive Micromixers at a Wide Range of Reynolds Numbers

by Vladimir Viktorov, Md Readul Mahmud and Carmen Visconte

Micromachines 2015, 6(8), 1166-1179; https://doi.org/10.3390/mi6081166 - 18 Aug 2015

Cited by 21 | Viewed by 5801

Abstract

Two novel passive micromixers, denoted as the Y-Y mixer and the H-C mixer, based on split-and-recombine (SAR) principle are studied both experimentally and numerically over Reynolds numbers ranging from 1 to 100. An image analysis technique was used to evaluate mixture homogeneity at [...] Read more.

Two novel passive micromixers, denoted as the Y-Y mixer and the H-C mixer, based on split-and-recombine (SAR) principle are studied both experimentally and numerically over Reynolds numbers ranging from 1 to 100. An image analysis technique was used to evaluate mixture homogeneity at four target areas. Numerical simulations were found to be a useful support for the design phase, since a general idea of mixing of fluids can be inferred from the segregation or the distribution of path lines. Comparison with a well-known mixer, the Tear-drop one, was also performed. Over the examined range of Reynolds numbers 1 ≤ Re ≤ 100, the Y-Y and H-C mixers showed at their exit an almost flat mixing index characteristic, with a mixing efficiency higher than 90%; conversely the Tear-drop mixer showed a relevant decrease of efficiency at mid-range. Furthermore, the Y-Y and the H-C showed significantly less pressure drop than the Tear-drop mixer. Full article

(This article belongs to the Special Issue Micromixer & Micromixing)

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3328 KiB

Open AccessArticle

Mixing Performance of a Serpentine Micromixer with Non-Aligned Inputs

by Shakhawat Hossain and Kwang-Yong Kim

Micromachines 2015, 6(7), 842-854; https://doi.org/10.3390/mi6070842 - 3 Jul 2015

Cited by 38 | Viewed by 6810

Abstract

In this study, a numerical investigation on mixing and flow structure in a serpentine microchannel with non-aligned input channels was performed. The non-aligned input channels generate a vortical flow, which is formed by incoming fluid streams through tangentially aligned channels. Mixing index was [...] Read more.

In this study, a numerical investigation on mixing and flow structure in a serpentine microchannel with non-aligned input channels was performed. The non-aligned input channels generate a vortical flow, which is formed by incoming fluid streams through tangentially aligned channels. Mixing index was evaluated to measure the degree of mixing in the micromixer. Analyses of mixing and flow field were investigated for a Reynolds number range starting from 0.1 to 120. The vortical structure of the flow was analyzed to find its effect on the mixing performance. Mixing of two working fluids in the micromixer was evaluated by using three-dimensional Navier–Stokes equations. In order to compare the mixing performance between the serpentine micromixers with and without non-aligned inputs, the geometric parameters, such as cross-section areas of the input channels and main channel, height of the channel, axial length of the channel, and number of pitches, were kept constant. Pressure drops were also calculated with fixed axial length in both cases. Full article

(This article belongs to the Special Issue Micromixer & Micromixing)

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1460 KiB

Open AccessArticle

Effects of Baffle Configuration on Mixing in a T-Shaped Micro-Channel

by Dong Jin Kang

Micromachines 2015, 6(6), 765-777; https://doi.org/10.3390/mi6060765 - 17 Jun 2015

Cited by 20 | Viewed by 5849

Abstract

A numerical study was performed for a T-shaped microchannel to enhance mixing performance through a baffle configuration. The mixing performance was analyzed in terms of the DOM (degree of mixing) and the pressure load between the two inlets and outlet. Four different baffle [...] Read more.

A numerical study was performed for a T-shaped microchannel to enhance mixing performance through a baffle configuration. The mixing performance was analyzed in terms of the DOM (degree of mixing) and the pressure load between the two inlets and outlet. Four different baffle configurations were designed and simulated to determine how they affect the mixing performance of a T-shaped microchannel. Among the four baffle configurations, a cyclic configuration of baffles produced the best results. It exhibited the fastest growth in the DOM along the microchannel. The cyclic configuration means that four baffles are attached to four side walls of the channel in a cyclic order. The mixing improvement occurs in two ways. One is in the baffle region, when the cyclic configuration causes the fluid flow to rotate in the cross section, unlike other configurations. The other improvement is observed in the remaining outlet branch after the baffle region. This improvement is due to twisting and elongation of the boundary between two fluids. The baffle size and the interval between two consecutive baffles are shown to be optimized in terms of the DOM for a given condition. Full article

(This article belongs to the Special Issue Micromixer & Micromixing)

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6499 KiB

Open AccessArticle

Optimized Simulation and Validation of Particle Advection in Asymmetric Staggered Herringbone Type Micromixers

by Eszter L. Tóth, Eszter G. Holczer, Kristóf Iván and Péter Fürjes

Micromachines 2015, 6(1), 136-150; https://doi.org/10.3390/mi6010136 - 30 Dec 2014

Cited by 26 | Viewed by 9705

Abstract

This paper presents and compares two different strategies in the numerical simulation of passive microfluidic mixers based on chaotic advection. In addition to flow velocity field calculations, concentration distributions of molecules and trajectories of microscale particles were determined and compared to evaluate the [...] Read more.

This paper presents and compares two different strategies in the numerical simulation of passive microfluidic mixers based on chaotic advection. In addition to flow velocity field calculations, concentration distributions of molecules and trajectories of microscale particles were determined and compared to evaluate the performance of the applied modeling approaches in the proposed geometries. A staggered herringbone type micromixer (SHM) was selected and studied in order to demonstrate finite element modeling issues. The selected microstructures were fabricated by a soft lithography technique, utilizing multilayer SU-8 epoxy-based photoresist as a molding replica for polydimethylsiloxane (PDMS) casting. The mixing processes in the microfluidic systems were characterized by applying molecular and particle (cell) solutions and adequate microscopic visualization techniques. We proved that modeling of the molecular concentration field is more costly, in regards to computational time, than the particle trajectory based method. However, both approaches showed adequate qualitative agreement with the experimental results. Full article

(This article belongs to the Special Issue Micromixer & Micromixing)

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4166 KiB

Open AccessArticle

The Effect of Inertia on the Flow and Mixing Characteristics of a Chaotic Serpentine Mixer

by Tae Gon Kang and Patrick D. Anderson

Micromachines 2014, 5(4), 1270-1286; https://doi.org/10.3390/mi5041270 - 27 Nov 2014

Cited by 20 | Viewed by 6521

Abstract

As an extension of our previous study, the flow and mixing characteristics of a serpentine mixer in non-creeping flow conditions are investigated numerically. A periodic velocity field is obtained for each spatially periodic channel with the Reynolds number (Re) ranging from 0.1 to [...] Read more.

As an extension of our previous study, the flow and mixing characteristics of a serpentine mixer in non-creeping flow conditions are investigated numerically. A periodic velocity field is obtained for each spatially periodic channel with the Reynolds number (Re) ranging from 0.1 to 70 and the channel aspect ratio from 0.25 to one. The flow kinematics is visualized by plotting the manifold of the deforming interface between two fluids. The progress of mixing affected by the Reynolds number and the channel geometry is characterized by a measure of mixing, the intensity of segregation, calculated using the concentration distribution. A mixer with a lower aspect ratio, which is a poor mixer in the creeping flow regime, turns out to be an efficient one above a threshold value of the Reynolds number, Re = 50. This is due to the combined effect of the enhanced rotational motion of fluid particles and back flows near the bends of the channel driven by inertia. As for a mixer with a higher aspect ratio, the intensity of segregation has its maximum around Re = 30, implying that inertia does not always have a positive influence on mixing in this mixer. Full article

(This article belongs to the Special Issue Micromixer & Micromixing)

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2413 KiB

Open AccessArticle

Mixing Analysis of Passive Micromixer with Unbalanced Three-Split Rhombic Sub-Channels

by Shakhawat Hossain and Kwang-Yong Kim

Micromachines 2014, 5(4), 913-928; https://doi.org/10.3390/mi5040913 - 22 Oct 2014

Cited by 62 | Viewed by 8821

Abstract

A micromixer with unbalanced three-split rhombic sub-channels was proposed, and analyses of the mixing and flow characteristics of this micromixer were performed in this work. Three-dimensional Navier-Stokes equations in combination with an advection-diffusion model with two working fluids (water and ethanol) were solved [...] Read more.

A micromixer with unbalanced three-split rhombic sub-channels was proposed, and analyses of the mixing and flow characteristics of this micromixer were performed in this work. Three-dimensional Navier-Stokes equations in combination with an advection-diffusion model with two working fluids (water and ethanol) were solved for the analysis. The mixing index and pressure drop were evaluated and compared to those of a two-split micromixer for a range of Reynolds numbers from 0.1–120. The results indicate that the proposed three-split micromixer is efficient in mixing for a range of Reynolds numbers from 30–80. A parametric study was performed to determine the effects of the rhombic angle and sub-channel width ratio on mixing and pressure drop. Except at the lowest Reynolds number, a rhombic angle of 90° gave the best mixing performance. The three-split micromixer with minimum minor sub-channel widths provided the best mixing performance. Full article

(This article belongs to the Special Issue Micromixer & Micromixing)

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8134 KiB

Open AccessArticle

Effect of β-PVDF Piezoelectric Transducers’ Positioning on the Acoustic Streaming Flows

by Susana O. Catarino, João Mário Miranda and Graça Minas

Micromachines 2014, 5(3), 654-666; https://doi.org/10.3390/mi5030654 - 1 Sep 2014

Cited by 4 | Viewed by 5903

Abstract

This paper reports the numerical and experimental analysis of the acoustic streaming effect in a fluidic domain. The actuation of a piezoelectric transducer generates acoustic waves that propagate to the fluids, generating pressure gradients that induce the flow. The number and positioning of [...] Read more.

This paper reports the numerical and experimental analysis of the acoustic streaming effect in a fluidic domain. The actuation of a piezoelectric transducer generates acoustic waves that propagate to the fluids, generating pressure gradients that induce the flow. The number and positioning of the transducers affect the pressure gradients and, consequently, the resultant flow profile. Two actuation conditions were considered: (1) acoustic streaming generated by a 28 μm thick β-poly(vinylidene fluoride) (β-PVDF) piezoelectric transducer placed asymmetrically relative to the fluidic domain and (2) acoustic streaming generated by two 28 μm thick β-PVDF piezoelectric transducers placed perpendicularly to each other. The transducers were fixed to the lower left corner of a poly(methyl methacrylate) (PMMA)cuvette and were actuated with a 24 Vpp and 34.2 MHz sinusoidal voltage. The results show that the number of transducers and their positioning affects the shape and number of recirculation areas in the acoustic streaming flows. The obtained global flows show great potential for mixing and pumping, being an alternative to the previous geometries studied by the authors, namely, a single transducer placed symmetrically under a fluidic domain. Full article

(This article belongs to the Special Issue Micromixer & Micromixing)

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Review

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3680 KiB

Open AccessReview

Modeling and Optimization of Y-Type Micromixers

by Valery Rudyak and Andrey Minakov

Micromachines 2014, 5(4), 886-912; https://doi.org/10.3390/mi5040886 - 20 Oct 2014

Cited by 66 | Viewed by 11091

Abstract

A trend in the global technological progress in the last few decades is the development of microsystem technology, microelectromechanical systems and corresponding technologies. Fluid mixing is an extremely important process widely used in various microfluidic devices (chemical microreactors, chemical and biological analyzers, drug [...] Read more.

A trend in the global technological progress in the last few decades is the development of microsystem technology, microelectromechanical systems and corresponding technologies. Fluid mixing is an extremely important process widely used in various microfluidic devices (chemical microreactors, chemical and biological analyzers, drug delivery systems, etc.). To increase the mixing rate, it is necessary to use special devices: micromixers. This paper presents the results of a hydrodynamic simulation of Y-shaped micromixers. Flows are analyzed for both low and moderate Reynolds numbers. The passive and active mixers are considered. The dependence of the mixing efficiency on the Reynolds and Péclet numbers, as well as the possibility of using the hydrophobic and ultra-hydrophobic coatings is analyzed. Five different flow regimes were identified: (1) stationary vortex-free flow (Re < 5); (2) stationary symmetric vortex flow with two horseshoe vortices (5 < Re < 150); (3) stationary asymmetric vortex flow (150 < Re < 240); (4) non-stationary periodic flow (240 < Re < 400); and (5) stochastic flow (Re > 400). The maximum mixing efficiency was obtained for stationary asymmetric vortex flow. Full article

(This article belongs to the Special Issue Micromixer & Micromixing)

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