Numerical Mixing Analysis of a Vaned Circular Micromixer

2006 ◽  
Author(s):  
Richard Bergman ◽  
Alexander Efremov ◽  
Pierre Woehl
Keyword(s):  
Numerical Analysis ◽  
Turbulent Mixing ◽  
Parametric Study ◽  
Large Scale ◽  
Acceptable Level ◽  
Mixing Efficiency ◽  
Mixing Process ◽  
Mixing Performance ◽  
Numerical Mixing ◽  
Cutting And Stacking

Mixing of fluids is a common and often critical step in microfluidic systems. In typical large scale processes turbulence greatly speeds the mixing process. At the mini and micro-scales, however, the flow is laminar and the benefits of turbulent mixing are not present. Mixing at the mini- and micro-scales tends to become a more highly engineered process of bringing fluids together in predictable ways to achieve a predetermined and acceptable level of mixing. This paper summarizes a numerical analysis of the mixing performance of a vaned circular micromixer. A newly developed mixing metric suitable for reacting fluids is developed for this study. Applying the basic steps of stretching, cutting, and stacking to effect mixing, a useful micromixer is analyzed numerically for its mixing efficiency. A parametric study of flow and viscosity indicate that a flow Re of 12 or higher is sufficient to achieve effective and rapid mixing in this device.

Flow Geometry Effects on the Turbulent Mixing Efficiency

2006 ◽  
Vol 128 (4) ◽  
pp. 874-879 ◽  
Author(s):  
Roberto C. Aguirre ◽  
Jennifer C. Nathman ◽  
Haris C. Catrakis
Keyword(s):  
Shear Layer ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Mixture Fraction ◽  
Mixing Efficiency ◽  
Developed Turbulence ◽  
Planar Shear ◽  
Flow Geometry ◽  
Schmidt Numbers ◽  
Geometry Effects

Flow geometry effects are examined on the turbulent mixing efficiency quantified as the mixture fraction. Two different flow geometries are compared at similar Reynolds numbers, Schmidt numbers, and growth rates, with fully developed turbulence conditions. The two geometries are the round jet and the single-stream planar shear layer. At the flow conditions examined, the jet exhibits an ensemble-averaged mixing efficiency which is approximately double the value for the shear layer. This substantial difference is explained fluid mechanically in terms of the distinct large-scale entrainment and mixing-initiation environments and is therefore directly due to flow geometry effects.

Numerical Simulation of Turbulent Mixing for Dislocated Blades in a Stirred Tank

2011 ◽  
Vol 354-355 ◽  
pp. 559-563
Author(s):  
Lei Shi ◽  
Shen Jie Zhou ◽  
Feng Ling Yang ◽  
Fan Jin Hu
Keyword(s):  
Numerical Simulation ◽  
Turbulent Mixing ◽  
Stirred Tank ◽  
Industrial Processes ◽  
Mixing Efficiency ◽  
Mixing Process ◽  
Flow Number ◽  
Stirred Tanks ◽  
Calculation Results ◽  
Better Than

Mixing efficiency is an important parameter in the design of many industrial processes in stirred tanks. In this study, CFD technology was used to simulate the mixing process inside the stirred tank with dislocated blades and standard turbine. Calculations were performed to study the effects of agitator speed and the configuration of impellers on mixing efficiency. The results showed that the flow field in the stirred tank with the dislocated blades is better than the standard turbine, and the flow number of the dislocated blades had been improved while the power number had been reduced. According to calculation results of Wr, we found the mixing efficiency of the dislocated blades had been improved about 4 times than that of standard turbine.

Experimental Measurement of the Vortex Development Downstream of a Lobed Forced Mixer

1992 ◽  
Vol 114 (1) ◽  
pp. 63-71 ◽  
Author(s):  
W. A. Eckerle ◽  
H. Sheibani ◽  
J. Awad
Keyword(s):  
Secondary Flow ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Vortex Breakdown ◽  
Velocity Ratio ◽  
Mixing Process ◽  
Mixing Processes ◽  
Design Variables ◽  
Secondary Motion ◽  
The Mean

An experimental study was conducted to investigate the mixing processes downstream of a forced mixer. A forced mixer generates large-scale, axial (stirring) vorticity, which causes the primary and secondary flow to mix rapidly with low loss. These devices have been successfully used in the past where enhanced mixing of two streams was a requirement. Unfortunately, details of the mixing process associated with these lobed forced mixers are not well understood. Performance sensitivity to design variables has not been documented. An experiment was set up to investigate the mixing processes downstream of a mixer. Air flow was independently supplied to each side of the forced mixer by separate centrifugal blowers. Pressures were measured at the entrance to the lobes with a pitot-static probe to document the characteristics of the approaching boundary layer. Interior mean and fluctuating velocities were nonintrusively measured using a two-component laser-Doppler velocimetry (LDV) system for velocity ratios of 1:1 and 2:1. The wake structure is shown to display a three-step process where initially secondary flow was generated by the mixer lobes, the secondary flow created counterrotating vortices with a diameter on the order of the convolute width, and then the vortices broke down resulting in a significant increase in turbulent mixing. The results show that the mean secondary motion induced by the lobes effectively circulated the flow passing through the lobes. This motion, however, did not homogeneously mix the two streams. Turbulent mixing in the third step of the mixing process appears to be an important element in the enhanced mixing that has been observed with forced mixers. The length required for the flow to reach this third step is a function of the velocity ratio across the mixer. The results of this investigation indicate that both the mean secondary motion and the turbulent mixing occurring after vortex breakdown need to be considered for prediction of forced mixer performance.

Experimental Measurement of the Vortex Development Downstream of a Lobed Forced Mixer

1990 ◽  
Author(s):  
Wayne A. Eckerle ◽  
Hamdi Sheibani ◽  
Jean Awad
Keyword(s):  
Secondary Flow ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Vortex Breakdown ◽  
Velocity Ratio ◽  
Mixing Process ◽  
Mixing Processes ◽  
Design Variables ◽  
Secondary Motion ◽  
The Mean

An experimental study was conducted to investigate the mixing processes downstream of a forced mixer. A forced mixer generates large scale, axial (stirring) vorticity which causes the primary and secondary flow to mix rapidly with low loss. These devices have been successfully used in the past where enhanced mixing of two streams was a requirement. Unfortunately, details of the mixing process associated with these lobed forced mixers are not well understood. Performance sensitivity to design variables has not been documented. An experiment was set up to investigate the mixing processes downstream of a mixer. Air flow was independently supplied to each side of the forced mixer by separate centrifugal blowers. Pressures were measured at the entrance to the lobes with a pitot-static probe to document the characteristics of the approaching boundary layer. Interior mean and fluctuating velocities were nonintrusively measured using a two-component Laser Doppler Velocimetry (LDV) system for velocity ratios of 1:1 and 2:1. The wake structure is shown to display a three step process where initially secondary flow was generated by the mixer lobes, the secondary flow created counter-rotating vortices with a diameter on the order of the convolute width, and then the vortices broke down resulting in a significant increase in turbulent mixing. The results show that the mean secondary motion induced by the lobes effectively circulated the flow passing through the lobes. This motion, however, did not homogeneously mix the two streams. Turbulent mixing in the third step of the mixing process appears to be an important element in the enhanced mixing that has been observed with forced mixers. The length required for the flow to reach this third step is a function of the velocity ratio across the mixer. The results of this investigation indicate that both the mean secondary motion and the turbulent mixing occurring after vortex breakdown need to be considered for prediction of forced mixer performance.

Turbulent mixing in a shear-free stably stratified two-layer fluid

1998 ◽  
Vol 354 ◽  
pp. 175-208 ◽  
Author(s):  
DAVID A. BRIGGS ◽  
JOEL H. FERZIGER ◽  
JEFFREY R. KOSEFF ◽  
STEPHEN G. MONISMITH
Keyword(s):  
Kinetic Energy ◽  
Froude Number ◽  
Internal Waves ◽  
Mixed Layer ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Source Region ◽  
Buoyancy Flux ◽  
Mixing Efficiency ◽  
Principal Mechanism

Direct numerical simulation is used to examine turbulent mixing in a shear-free stably stratified fluid. Energy is continuously supplied to a small region to maintain a well-developed kinetic energy profile, as in an oscillating grid flow (Briggs et al. 1996; Hopfinger & Toly 1976; Nokes 1988). A microscale Reynolds number of 60 is maintained in the source region. The turbulence forms a well-mixed layer which diffuses from the source into the quiescent fluid below. Turbulence transport at the interface causes the mixed layer to grow under weakly stratified conditions. When the stratification is strong, large-scale turbulent transport is inactive and pressure transport becomes the principal mechanism for the growth of the turbulence layer. Down-gradient buoyancy flux is present in the large scales; however, far from the source, weak counter-gradient fluxes appear in the medium to small scales. The production of internal waves and counter-gradient fluxes rapidly reduces the mixing when the turbulent Froude number is lower than unity. When the stratification is weak, the turbulence is strong enough to break up the density interface and transport fluid parcels of different density over large vertical distances. As the stratification intensifies, turbulent eddies flatten against the interface creating anisotropy and internal waves. The dominant entrainment mechanism is then scouring. Mixing efficiency, defined as the ratio of buoyancy flux to available kinetic energy, exhibits a similar dependence on Froude number to other stratified flows (Holt et al. 1992; Lienhard & Van Atta 1990). However, using the anisotropy of the turbulence to define an alternative mixing efficiency and Froude number improves the correlation and allows local scaling.

Numerical analysis of mixing performance of mixing section in pin-barrel single-screw extruder

2011 ◽  
Vol 31 (1) ◽  
Author(s):  
Jinnan Chen ◽  
Pan Dai ◽  
Hui Yao ◽  
Tung Chan
Keyword(s):  
Numerical Analysis ◽  
Finite Elements ◽  
Flow Field ◽  
Residence Time ◽  
Particle Tracking ◽  
Mixing Efficiency ◽  
Screw Extruder ◽  
Mixing Performance ◽  
Single Screw ◽  
Single Screw Extruder

Abstract Using the finite elements method, numerical simulations of the flow field of a rubber melt in the mixing sections of a conventional full-flight single-screw extruder and a pin-barrel single-screw extruder were carried out. Particle tracking analysis was used to statistically analyze the mixing state of the rubber melt in the mixing section with pin and that without pin. The mixing performance of both types of mixing section was quantitatively evaluated. The results show that the pins partially disorganize the particle trajectories, change the particle moving directions, and enhance the mixing performance. The particle residence time is longer in the mixing section with pins than in the mixing section with no pin, leading to better mixing in the former. The distributive mixing of particles in both types of mixing section was statistically analyzed. The pins increase the efficiency of stretching and the time-averaged efficiency of stretching, and hence the mixing efficiency. However, further increase in the number of pins does not necessarily enhance the mixing performance.

Numerical Simulation of Intermittent-Controlled Multiple Jets

2019 ◽  
Author(s):  
Koichi Tsujimoto ◽  
Kango Kitahara ◽  
Toshihiko Shakouchi ◽  
Toshitake Ando
Keyword(s):  
Numerical Simulation ◽  
Large Scale ◽  
Near Field ◽  
Vortex Structures ◽  
Mixing Efficiency ◽  
Intermittent Control ◽  
Mixing Performance ◽  
Multiple Jets ◽  
Inflow Condition ◽  
And Diffusion

Abstract Multiple jets are used in industrial processes such as combustion, ventilation and so on, and their improvement of mixing and diffusion is demanded. Unlike single jet, since the jets issuing from nozzles will coalescence, merge or combine with each other, it is necessary to reduce mixing performance such as entrainment from surroundings and spreading into surroundings. It is well known that the characteristics such as mixing and diffusion of the jet are strongly dependent on the large-scale vortex structures being formed near the nozzles. Therefore, an appropriate inflow condition at a nozzle is capable of controlling the large vortex structures near field around the nozzle and improves the mixing performance. In this study, we examine an intermittent control of jets varying the control frequency and the jet spacing so as to reduce the interaction between each jet. We conduct the DNS (direct numerical simulation) of intermittently-controlled two round jets. In order to quantify the mixing efficiency of the intermittent control, statistical entropy and entrainment are examined. Compared to the uncontrolled jet, it is confirmed that the mixing efficiency is markedly improved, suggesting that the intermittent control can be expected to be useful for the improvement of mixing performance of multiple jets.

Rotating Horizontal Convection

2021 ◽  
Vol 54 (1) ◽  
Author(s):  
Bishakdatta Gayen ◽  
Ross W. Griffiths
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Mixing Efficiency ◽  
Small Scale ◽  
Annual Review ◽  
Publication Date ◽  
Geostrophic Balance ◽  
Horizontal Convection ◽  
Planetary Rotation ◽  
Circumpolar Current

Global differences of temperature and buoyancy flux at the ocean surface are responsible for small-scale convection at high latitudes, global overturning, and the top-to-bottom density difference in the oceans. With planetary rotation the convection also contributes to the large-scale horizontal, geostrophic circulation, and it crucially involves a 3D linkage between the geostrophic circulation and vertical overturning. The governing dynamics of such a surface-forced convective flow are fundamentally different from Rayleigh–Bénard convection, and the role of buoyancy forcing in the oceans is poorly understood. Geostrophic balance adds to the constraints on transport in horizontal convection, as illustrated by experiments, theoretical scaling, and turbulence-resolving simulations for closed (mid-latitude) basins and an annulus or reentrant zonal (circumpolar) channel. In these geometries, buoyancy drives either horizontal mid-latitude gyre recirculations or a strong Antarctic Circumpolar Current, respectively, in addition to overturning. At large Rayleigh numbers the release of available potential energy by convection leads to turbulent mixing with a mixing efficiency approaching unity. Turbulence-resolving models are also revealing the relative roles of wind stress and buoyancy when there is mixed forcing, and in future work they need to include the effects of turbulent mixing due to energy input from tides. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 54 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Effect of Electrode Configurations on the Performance of Electro-Hydrodynamic Micromixer

2018 ◽  
Author(s):  
Hak-Sun Kim ◽  
Hyun-Oh Kim ◽  
Youn-Jea Kim
Keyword(s):  
Numerical Analysis ◽  
Chemical Engineering ◽  
Fine Particles ◽  
Comsol Multiphysics ◽  
Mixing Efficiency ◽  
Flow Conditions ◽  
Mixing Performance ◽  
Zeta Potentials ◽  
Particle Mixing ◽  
Geometrical Effects

Micromixers are widely used in chemical engineering and bioengineering industries. In this study, geometrical effects of electrodes were investigated to mix fine particles affected by external electric field. In order to improve the particle mixing performance of micromixer, the electroosmosis effect could be utilized with configuration of electrodes at the top and bottom of microchannel. Numerical analysis was performed to derive the pattern of electrodes with superior mixing efficiency by changing voltages and zeta potentials applied to the micromixer channel, by using COMSOL Multiphysics 5.2. The results of mixing performance were graphically depicted with various arrangements of electrode and flow conditions.

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