Application of Unbalanced Collisions of Fluid Streams in Microchannel for Mixing
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Experimental and numerical study has been carried on the proposed on design of the micromixer based on the unbalanced split and collision of the fluids streams. The main microchannel is split into two sub-channels and then recombines after a certain distance. The shape of the split sub-channels is rhombic with major subchannel crossing the minor sub-channel. Numerical analysis has been carried out by solving Navier-Stokes equation. The experimental study has been carried on the device fabricated using standard soft lithography technique. Mixing analysis has been performed using inverted fluorescence microscope. The micromixer with balanced collisions (equal width of sub-channels) shows poor mixing quality. The collision of the fluids streams are effective in enhancing mixing as the level of unbalance is increased by adjusting the widths of the sub-channels.Keywords:
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This paper reports the development of a 3-D passive micromixer named the overbridge-shaped micromixer (OBM), which can achieve fast mixing by taking advantage of the splitting, recombination, and chaotic advection mechanisms simultaneously. A scheme with the splitting channels of unequal widths is proposed for tremendously enhancing the mixing uniformity in the regions closing to the side walls. The channel depth-to-width ratio is the key factor to mixing performance. A four-unit OBM has been successfully fabricated via a multilayer polydimethylsiloxane process, and the total length of the OBM is <2 mm. Up to a 90% efficiency has been achieved within a Reynolds number (Re) range from 0.01 to 200 by numerical analysis, and the same mixing efficiency was also proven experimentally within a Re range from 0.01 to 50. A high efficiency of 90% was also obtained when mixing two fluids with different flow rates at the two inlets ranging from a ratio of 1:9 to 9:1. [2014-0186]
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Effective mixing gives strong advantageous impact on microfluidic applications since mixing is in general very slow process motivated by molecular diffusion transport only on the micro-scale. In this work, the mixing characteristics are analyzed in a Y-channel micromixer with obstacles. For the through analysis, our laboratory in-house unstructured grid CFD code is validated through solving a concentration transport in a uniform microchannel. The solutions well correspond to both exact solutions and those from MemCFD. Mixing in a Y-channel micromixer with obstacles is numerically investigated by the in-house code to search the optimal radius and layout of obstacles. From the simulations, the mixing efficiency appears to be proportional to the magnitude of the formation of lateral velocity component. It is also shown that the asymmetric layout and radius enlargement of obstacles greatly improves mixing efficiency.
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We are presenting experimental studies and numerical simulations to analyze an actively controlled mixer. The current design of the micromixer is called “shear superposition micromixer”. This micromixer consists of a main mixing channel where unmixed fluids are perturbed by jet flows emanating from series of transverse channels. Mixing of two fluids is achieved using the kinetic of the side jet flows. We quantify, numerically and experimentally, the degree of mixing achieved using the Mixing Variance Coefficient (MVC). We present some flow properties. Single channel mixing can be very good when amplitude and frequency are chosen carefully.
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An effective passive micromixer based on the principles of asymmetric split and recombine has been designed, developed, and investigated to enhance the mixing performance of the micromixer in a microfluidic system. The effects of geometrical parameters and the number of mixing units on mixing performance were studied at different Reynolds (Re) number (ranging from 1 to 80) via CFD software ANSYS CFX. The results revealed that the preferable number of mixing units is 6, and the optimal direction of reducer is opposite to the main channel flow; the D-shaped mixing channel forces the mixed fluid to produce the extended vortex and Dean vortices simultaneously which caused a strong collision at the confluence of fluids, thus leading to the superposition and enhancement of the vortex system; when Re number is 80 and the width ratio of mixing channel W 2/W 3 = 1, the mixing efficiency of micromixer can exceed 95%.
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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.
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A design for modified planar passive micromixer based on the concept of vortex-generated structure enhanced mixing is described in this work.By using computational fluid dynamics CFD-ACE+,three-dimensional numerical simulation and structural optimization for mixing were performed in order to reveal the structural influence on the flow feature and mixing characteristics.Experimental data were used to validate the numerical analysis.The computational and experimental results for the concentration distributions and flow patterns demonstrate that the expansion vortices,separated vortices and Dean vortices appear in the curved channel of this modified micromixer,which is arranged to vortex-generated structures.The combination and enhancement of the vortex system increase the fluid disturbance,effectively improving the contact area of fluid and accelerating the mixing process.Based on comprehensive consideration of mixing efficiency and pressure drop distribution,the structural design adopts the vortex-generated structure with regular arrangement,and the gap width ratio Wd/W,thickness-width ratio B/W,and arrangement angle θa are equal to 1/4,3/10,and 120°,respectively.Significant mixing effect of fluid in the micromixer can be realized in a wide range of Reynolds number.
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Micromixing
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