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.

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.

Velocity measurements close to the bed in a wave tank

1970 ◽  
Vol 42 (1) ◽  
pp. 111-123 ◽  
Author(s):  
J. F. A. Sleath
Keyword(s):  
Velocity Distribution ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Flow Conditions ◽  
Velocity Measurements ◽  
Dominant Effect ◽  
Wave Tank ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
Laminar Flow Conditions

Measurements of the velocity distribution close to the bed have been made under laminar flow conditions in a wave tank. The classical solution for the velocity distribution was found to be valid when the bed was smooth, but considerable deviations between theory and experiment were observed with beds of sand. It is suggested that these deviations were caused by vortex formation around the grains of sand. The similarity between the velocity profiles obtained in these tests and those reported by other writers under supposedly turbulent conditions suggests that even at high Reynolds numbers vortex formation may continue to be the dominant effect in oscillatory boundary layers of this sort.

scholarly journals Numerical Analysis of the Heterogeneity Effect on Electroosmotic Micromixers Based on the Standard Deviation of Concentration and Mixing Entropy Index

Micromachines ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1055
Author(s):  
Alireza Farahinia ◽  
Jafar Jamaati ◽  
Hamid Niazmand ◽  
Wenjun Zhang
Keyword(s):  
Reynolds Number ◽  
Zeta Potential ◽  
Electroosmotic Flow ◽  
Molecular Diffusion ◽  
Slip Surface ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Slip Coefficient ◽  
Mixing Rate ◽  
Heterogeneous Distribution

One approach to achieve a homogeneous mixture in microfluidic systems in the quickest time and shortest possible length is to employ electroosmotic flow characteristics with heterogeneous surface properties. Mixing using electroosmotic flow inside microchannels with homogeneous walls is done primarily under the influence of molecular diffusion, which is not strong enough to mix the fluids thoroughly. However, surface chemistry technology can help create desired patterns on microchannel walls to generate significant rotational currents and improve mixing efficiency remarkably. This study analyzes the function of a heterogeneous zeta-potential patch located on a microchannel wall in creating mixing inside a microchannel affected by electroosmotic flow and determines the optimal length to achieve the desired mixing rate. The approximate Helmholtz–Smoluchowski model is suggested to reduce computational costs and simplify the solving process. The results show that the heterogeneity length and location of the zeta-potential patch affect the final mixing proficiency. It was also observed that the slip coefficient on the wall has a more significant effect than the Reynolds number change on improving the mixing efficiency of electroosmotic micromixers, benefiting the heterogeneous distribution of zeta-potential. In addition, using a channel with a heterogeneous zeta-potential patch covered by a slip surface did not lead to an adequate mixing in low Reynolds numbers. Therefore, a homogeneous channel without any heterogeneity would be a priority in such a range of Reynolds numbers. However, increasing the Reynolds number and the presence of a slip coefficient on the heterogeneous channel wall enhances the mixing efficiency relative to the homogeneous one. It should be noted, though, that increasing the slip coefficient will make the mixing efficiency decrease sharply in any situation, especially in high Reynolds numbers.

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.

Vortex formation of a finite-span synthetic jet: High Reynolds numbers

2014 ◽  
Vol 26 (1) ◽  
pp. 014101 ◽  
Author(s):  
Tyler Van Buren ◽  
Edward Whalen ◽  
Michael Amitay
Keyword(s):  
Vortex Formation ◽  
Reynolds Numbers ◽  
Synthetic Jet ◽  
Finite Span ◽  
High Reynolds Numbers ◽  
High Reynolds

Numerical Simulation of a Novel Passive Micromixer With Curved Channel and Slanted Grooves

2010 ◽  
Author(s):  
Yanfeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Numerical Simulation ◽  
Rotation Angle ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Curved Channel ◽  
Passive Micromixer ◽  
Present Design ◽  
High Reynolds ◽  
Rotation Strength

A novel passive micromixer with slanted grooves on the top and bottom of curved microchannel, denoted as CMG, is investigated numerically. The total mixing length is fixed at approximate 5.17 mm. The curved channel is applied to generate Dean vortices in the microchannel at high Reynolds numbers. The slanted grooves are used to assist to create the rotation of flow at low Reynolds numbers. The validation of present numerical simulation is done through the comparison with literatures. Three parameters, the slanted angle (θ), the grooves width angle (ω), and the height ratio of grooves (Hg/H), are selected to achieve the optimization. The tested Reynolds numbers range from 1 to 50. Compared with slanted grooved micromixer (SGM) and the curved microchannel (CM), the present micromixer has better mixing efficiency. In order to investigate the flow characteristics, a particle located at one inlet is selected and the trajectory is performed to observe the flow rotation. The rotation angle is defined to estimate the rotation strength. The results show that CMG has largest rotation angle than CM and SGM, which indicates a stronger rotation/helical motion generated in the curved channel. The mixing efficiency of present design has 60% at Re = 50 with a pressure drop of 1.8 kPa.

Circulation in liquid drops

1959 ◽  
Vol 252 (1271) ◽  
pp. 457-475 ◽  
Keyword(s):  
Interfacial Tension ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Critical Value ◽  
Spherical Drop ◽  
Liquid Drops ◽  
Surface Active Agents ◽  
Surface Active ◽  
High Reynolds ◽  
Internal Velocity

A number of aspects of the motion of drops through liquids are discussed with a view to clarifying the physical picture of the mechanism by which the liquid/liquid interface influences the transfer of momentum and mass across it. Internal motion and distortion are shown to affect drag characteristics at relatively high Reynolds numbers (100 to 1000). The Hadamard and Hill vortex models are compared. The internal velocity distribution in a spherical drop is shown to agree with both models but external motion in the Stokesian region is only predicted by the former. At higher Reynolds numbers where a potential flow regime prevails, the external motion is more closely described by Hill’s model. Vortices do not form in a drop until the Reynolds number reaches a critical value depending on the state of the interface and the viscosity of the drop liquid. Bond & Newton (1928) predicted that interfacial tension was the only variable affecting the transition but additional effects due to impurities and to the polarities of the component liquid molecules are also important, not only regarding the onset of vortex formation but also in relation to the extensiveness of circulation when under way. The presence of impurities such as very small concentrations of surface-active agents, although lowering the interfacial tension, greatly reduces the velocity of circulation in the vortex.

Vortex Formation for Different Geometry of Cavities Using High Reynolds Number

2014 ◽  
Vol 699 ◽  
pp. 416-421
Author(s):  
Mohd Noor Asril Saadun ◽  
Muhammad Zulhakim Sharudin ◽  
Nor Azwadi Che Sidik ◽  
Mohd Hafidzal Mohd Hanafi
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Stokes Equations ◽  
Vortex Formation ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Contaminant Removal ◽  
Navier Stokes Equations ◽  
High Reynolds

A preliminary study of Computational Fluid Dynamics (CFD) on the effect of high Reynolds numbers in the cavity has been carried out. Two dimensional model analysis of the flow characteristics were conducted using the numerical solution of Navier-Stokes equations based on the finite difference method. The flow characteristics in the cavity and the driven flow were modeled via turbulence equation modelling. This paper focuses on the effects of different high Reynolds number on the flow pattern of contaminant removal in the cavity. Different types of geometry and aspect ratio of the geometry were used as the parameters of the cavity in this study. Based on visualization of flows between each model with the different parameters used, the results of a comparison analysis focusing on the behavior of the flow were reported.

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.

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