Micro Mixers

Micro MixersMicro Mixers

ME 595ME 595Special Topics in Mechanical Engineering – Micro FluidicsSpecial Topics in Mechanical Engineering – Micro Fluidics

Western Michigan UniversityWestern Michigan University

Presented by:

John TomasiNovember 30th, 2004

Presentation for:

Dr. Liou’s ME 595/695 class

Micro MixersMicro Mixers J. TomasiJ. Tomasi

Macroscopically, mixing is usually Macroscopically, mixing is usually accomplished through turbulenceaccomplished through turbulence

II. Introduction to Mixing. Introduction to Mixing

transverse velocity componentstransverse velocity components

spontaneous flow fluctuationsspontaneous flow fluctuations folding and stretching of fluid particlesfolding and stretching of fluid particles

Chaotic behavior that randomly redposits Chaotic behavior that randomly redposits particles until homogeneity is achievedparticles until homogeneity is achieved

An everyday occurrence that is An everyday occurrence that is usually taken for grantedusually taken for granted


Microscopically, turbulence is difficult Microscopically, turbulence is difficult to achieveto achieve

II. Introduction to Mixing. Introduction to Mixing

reduced length scale results in low reduced length scale results in low Re and highly Re and highly laminarlaminar flows flows

fluids tend to move in layersfluids tend to move in layers mixing is achieved solely through mixing is achieved solely through

diffusion along the fluid-fluid boundarydiffusion along the fluid-fluid boundary

Dl

mixt 2

2lPey DUlPe

slow and/or lengthy processslow and/or lengthy process PPééclet Number is ~ 100, clet Number is ~ 100,


IIII. Importance of Mixing. Importance of Mixing

Sample AnalyzingSample Analyzing

Chemical Reaction KinematicsChemical Reaction Kinematics

Drug/Sample DeliveryDrug/Sample Delivery

proteinsproteins DNADNA

Additional laboratory procedures necessary Additional laboratory procedures necessary for a laboratory to fit on a “chip”for a laboratory to fit on a “chip”


ActiveActive

IIIIII. Types of Mixers. Types of Mixers

All micro mixing devices and techniques All micro mixing devices and techniques that utilize devices separate from the that utilize devices separate from the flow channel to induce mixing.flow channel to induce mixing.

All micro mixing devices and All micro mixing devices and techniques that operate independent techniques that operate independent of external intervention.of external intervention.

PassivePassive


Electro-osmosis with AC current appliedElectro-osmosis with AC current applied

IVIV. Active Mixers. Active Mixers

mixing occurs at particular frequenciesmixing occurs at particular frequencies

operation credited to instability that operation credited to instability that develops at particular frequenciesdevelops at particular frequencies

experimentally shown to reduce mixing experimentally shown to reduce mixing time from 500 sec. to as low as 3 sec.time from 500 sec. to as low as 3 sec.


Electro-osmosis with AC current appliedElectro-osmosis with AC current applied


• Advantages:Advantages:

◦ requires high voltagerequires high voltage

• Disadvantages:Disadvantages:

◦ utilizes common microfluidics deviceutilizes common microfluidics device

◦ sensitive to contaminates in the systemsensitive to contaminates in the system

◦ only low flow rates createdonly low flow rates created


Orthogonal PerturbationsOrthogonal Perturbations


transverse velocity components transverse velocity components artificially created by periodic injectionsartificially created by periodic injections

cross-flow establishes folding of fluid layerscross-flow establishes folding of fluid layers

operates best with particular operates best with particular injection frequenciesinjection frequencies


Orthogonal PerturbationsOrthogonal Perturbations



Electrowetting-On-Dielectric (EWOD)Electrowetting-On-Dielectric (EWOD)


droplet baseddroplet based• sandwiched bi-fluid droplet sandwiched bi-fluid droplet

with only two sides of contactwith only two sides of contact

matrix of electrically charged plates matrix of electrically charged plates direct droplet to roll in a box patterndirect droplet to roll in a box pattern

each complete roll increases the number each complete roll increases the number of fluid interfaces exponentially (2of fluid interfaces exponentially (2nn))

• BC’s allow fluid layers to fold BC’s allow fluid layers to fold as droplet movesas droplet moves








◦ complex constructioncomplex construction


◦ requires only 30 Vrequires only 30 Vrmsrms

◦ small throughputsmall throughput

◦ experimentally shown to reduce experimentally shown to reduce mixing times by as much as 50xmixing times by as much as 50x

◦ compactcompact


Serpentine and Helical ChannelSerpentine and Helical Channel

VV. Passive Mixers. Passive Mixers

fluids mix while the follow a winding fluids mix while the follow a winding pathpath

• operating principle: chaotic advectionoperating principle: chaotic advection


Serpentine and Helical ChannelSerpentine and Helical Channel



◦ effective in flows with Re > 1effective in flows with Re > 1


◦ compactly places long channel required compactly places long channel required for diffusive mixing on a microdevicefor diffusive mixing on a microdevice

◦ helical channel extremely difficult helical channel extremely difficult to constructto construct

◦ no great reductions in mixing timesno great reductions in mixing times

◦ very simple to operatevery simple to operate


Staggered Herringbone Mixer (SHM)Staggered Herringbone Mixer (SHM)


raised ridges on the channel floor cause raised ridges on the channel floor cause the fluids to rotate within the channelthe fluids to rotate within the channel

• increases contact area and increases contact area and induces layer foldinginduces layer folding

various configurations of ridgesvarious configurations of ridges

Requires ridge heights of only 20 -Requires ridge heights of only 20 -30 % of mean channel height30 % of mean channel height


Staggered Herringbone Mixer (SHM)Staggered Herringbone Mixer (SHM)



◦ superiority to regular channels superiority to regular channels increases with flow velocityincreases with flow velocity

◦ requires only one additional step requires only one additional step during the construction phase over during the construction phase over regular channelsregular channels

◦ 1cm/s flow in 1001cm/s flow in 100μμm square channel requires 100cm for m square channel requires 100cm for diffusion alone, but only 1 cm with SHMdiffusion alone, but only 1 cm with SHM

◦ functions independent of Re for Re<100functions independent of Re for Re<100

◦ same fluid in the same channels flowing at 10cm/s would same fluid in the same channels flowing at 10cm/s would require 1,000cm for diffusion, but only 1.5 cm for SHMrequire 1,000cm for diffusion, but only 1.5 cm for SHM


Hydrodynamic FocusingHydrodynamic Focusing


achieves mixing by reducing the achieves mixing by reducing the layer thickness over which diffusion layer thickness over which diffusion must operatemust operate

◦ the thickness of each layer the thickness of each layer is controlled by its injection is controlled by its injection raterate

utilizes a microjet and two side channels to utilizes a microjet and two side channels to create three thin fluid layerscreate three thin fluid layers








◦ best suited for reaction kinematics best suited for reaction kinematics investigationsinvestigations


◦ extremely quick mixing times – as extremely quick mixing times – as low as 10 and 20 low as 10 and 20 μμss

◦ small volume consumption ~ 5nsmall volume consumption ~ 5nll/s/s

◦ properties of system well understoodproperties of system well understood


Droplet Based Recirculating FlowDroplet Based Recirculating Flow


recirculating flow within droplet folds fluid recirculating flow within droplet folds fluid layers into one anotherlayers into one another

• requires that “channel fluid” and droplet requires that “channel fluid” and droplet fluid be immisciblefluid be immiscible

• ““twirling” of droplet tip initiates mixingtwirling” of droplet tip initiates mixing

• surface tension between water and “channel surface tension between water and “channel fluid” must be greater than between water fluid” must be greater than between water and droplet fluidsand droplet fluids

droplet length controlled by relative injection droplet length controlled by relative injection raterate

fluids to be mixed and water are injected into a fluids to be mixed and water are injected into a stream of fluid moving through a microchannelstream of fluid moving through a microchannel








◦ restrictive on fluid combinationsrestrictive on fluid combinations


◦ quick mixing times ~ as low as 25 quick mixing times ~ as low as 25 μμss

◦ droplet length needs to be within a droplet length needs to be within a specific range for efficient mixingspecific range for efficient mixing


ThankThank You Youfor listeningfor listening

Questions?Questions?ThankThank You You

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Micro Mixers