operation of miccro fluid

MF Effects & Phenomena: 09 Basic Fluidic Elements / slide 1www.imtek.de/anwendungen

What? Lab tour

When? February 10th 2012

. 10:00 am

Where? 101 - SR 01-009/13

Microfluidics 1: Effects & Phenomena


01 Introduction to Microfluidics

02 Fluid Properties

03 Fluid Dynamics

04 Diffusion

05 Surface Tension

06 Heat-Phenomena

07 Electrokinetics

08 Design & Analysis

09 Basic Fluidic Elements

Microfluidics 1: Effects & Phenomena


Control of fluid flow

• Control of fluids by valves Flow rectifier Electrical equivalent diode

• Transport of fluids by pumps Composed of valves … and actuation unit

• Against „external” forces / fields Gravity Pressure gradient Viscosity etc.

• “Micro” implies … … small device size or … control of small volumes A uslass

K eram ik

D ruck-ansch luss

E n tlü ftung

G ehäuse

pressure portoutletport

ceramics

housing

Microvalve MegaMic Series HSG-IMITHoerbiger-Origa


Valve classifications

Passive valves

• No external actuation

• Interplay with geometrical structure

• Fluid flow … … controlled by hydrodynamic pressure

(p1 –p2) … built up by flow itself

Active Valves

• Flow control elements with actuators

• Control of fluid flow in binary or continuous fashion Binary „switch“ (open and close position) Continuous control (adjustment of flow rate

between open and close)

valve membrane

valve seatsilicon

flow channel

0,5

mm

A nsch luß 1 A nsch luß 2

membrane actuator



9.1 Valves

9.1.1 Valves without moving parts

9.1.2 Check valves

9.1.3 Active valves

9.2 Pumps

9.3 Mixing

9.4 Separating

9.5 Useful microfluidic structures

Passive Valves


Valves without moving parts

Special form of “passive valves” also known as ”fixed geometry valves”

• Single use valve Hydrophobic barriers see chapter “5. surface tension”

• Multi use valves Diffuser/nozzle valves Tesla valves

Basic working principle of multi use valves

• Difference in flow resistance (~ 10%) between flow direction … … forward … backward

• … for high flow rates (Re > 1)


Diffuser-nozzle valves (1)

• Transfer of kinetic energy (i.e. velocity) into potential energy (i.e. pressure)

• Flow IV through constriction

IV = const

• Static rectification efficiency as a general number of merit of a passive valve : pressure drop coefficient

Optimum working range for = 5°-20°

: 3.6 @ = 5°

A. Olson; Valveless Diffuser Micropumps; Stockholm 1998

diffuser

nozzle


Diffuser-nozzle valves (2)

• Advantages Simple structure Compact size

• Drawbacks Low forward-backward ratio High leakage rate

Diffuser direction

Nozzle direction

A. Olson; Valveless Diffuser Micropumps; Stockholm 1998

Rdiffuser < Rnozzle

No flow rectifier for small ReNo flow rectifier for small Re


Tesla valve (1)

• Bypass with deviating angles

• Asymmetric flow resistance

• Flow different in both directions due to inertia effects caused by high flow rates (high kinetic energy)

forward backwards

Rforward < Rbackward


Tesla valve (2)

• Advantages: Simple structure Compact size

• Drawbacks: Low forward-backward ratio High leakage rate

• Difference in flow resistance ~ 10% can be improved by serial connection of fixed geometry valves

backwards© Français, Bendib, ESIEE



9.1 Valves


9.1.2 Check valves

9.1.3 Active valves

9.2 Pumps

9.3 Mixing

9.4 Separating

9.5 Useful Microfluidic Structures

Passive Valves


Check valves

• Passive valves (with movable parts)

• Controlled by hydrodynamic pressure (p1 –p2) Built up by flow itself Interplay with geometrical structure

• Flow rate governed by Fluidic resistance of constriction Fluidic capacity of moving part

• Frequency (typical 10-100 Hz)

• Risk of clogging by particlesvalve membrane

valve seat

silicon

flow channel

0,5

mm

p1

p2


Characteristics

• Delayed response of membrane moving to pressure gradient

• Electrical equivalent Flow through constriction Membrane acts as capacitance Valve act as low-pass filter

• At high frequencies (~ kHz range) Only motion of valve membrane No net flow (net flow would have to go

through the resistance)

valve membrane

valve seatsilicon

flow channel

0,5

mm

p1

p2


Valve types – membrane valves

• Building blocks Membrane fixed in the periphery Central orifice Sealing area

• Advantages: High actuation forces due to large

effective area for pressure (F = pA) Large flow rate

• Drawbacks: Large size Large capacitance Large dead volume Low resonance frequency

valve membrane

valve seatsilicon

flow channel

0,5 m

m


Valve types – flap valves

• Building blocks Unilaterally fixed flap Opening underneath end of flap

• Advantages: Compact size Low capacitance Moderate dead volume High resonance frequency

• Drawbacks: Low actuation force

due to low effective area (F = pA) Small flow rate

Ve n t i lk la p p e S i l iz iu m

K la p p e n a u f la g e

flap silicon

valve plate



9.1 Valves


9.1.2 Check valves

9.1.3 Active valves

9.2 Pumps

9.3 Mixing

9.4 Separating


Passive Valves


Active valves

• Valves with actuators, for independent control of flow from flow parameters (pressure and/or flow)

Sub-Categories (classification)

• Binary „switch“ open and close position

• Continuous control continuous adjustment of flow rate from open to close

A nsch luß 1 A nsch luß 2 A nsch luß 1 A nsch luß 2

closed open

port 1 port 2 port 1 port 2


Overview on microvalve actuation principles

• Thermal actuators

• Piezoelectric actuation

• Electrostatic actuation

• Electromagnetic actuation

• Pneumatic actuation

• Hydrogel actuators

• Osmotic pumping

• Vapor pressure

• Phase change

• …



9.1 Valves

9.2 Pumps

9.2.1 Microdisplacement pumps

9.3 Mixing

9.4 Separating



Microdisplacement pumps

• Pump effect results from complex coupling between … Mechanical displacer Rectifier, e.g. valve

• Actuation of (passive) check valves by pressure within pump chamber

• External controllability Limited to membrane (displacer) Valves react on pressure gradients

• Motion of displacer governed by Actuator Inner pressure etc.

pump cycle

supply mode underpressure

pump mode overpressure


Design issues

Market requirements

• High pump rate against high backpressure

• Fail-safe pump

“Bubble-tolerance” & “self priming”

• Trapped gas bubbles in pump chamber are highly compressible

• Malfunctioning of displacement principle

• Solution: high compression ratios

Clogging

• Particles carried by liquid Solution: prefiltering of liquids

• High viscosity fluids

Forschungszentrum Karlsruhe

IMM-Mainz

FhG-IFT: 1996


Evolution of microdisplacement pumps

1980peris ta ltische Verdrängerpum pe

Milestones in evolution ofmicrodisplacement pumps

peristaltic displacement pumps


Peristaltic micromembrane pump

• J.G. Smits; MESA; 1983 „Piezoelectric micropump for peristaltic fluid displacement“; Patent NL 8302860

• 3 active displacers (microvalves)

• Piezoelectric actuation


Milestones


19 88Verdränge rpum pe m it R ück sch la gventile n



displacement pumps with check valves


Displacement pump with check valves

• H. van Lintel et al.; MESA, 1988 „A piezoelectric micropump based on micromachining of silicon“

• Piezoelectric actuated displacer

• Two membrane valves


increasing pumprate

Characteristics of membrane pumps (diaphragm pumps)

frequency [Hz]back pressure [mbar = cm H2O]

flow

[µ

L/m

in]

flow

[µ

L/m

in]

capacity of valve dominates


Milestones



1993ventillose Verdrängerpu m pe




valve less displacement pumps


Fixed-geometry valves – diffuser/nozzle

• G. Stemme et al.; KTH; Stockholm, 1993 „A novel piezoelectric valve-less fluid pump “


• Diffuser / nozzle as rectifier

P ie z o a k to r M e m b ra npiezo membrane

outletinlet

diffuser/nozzle element


Fixed geometry valve – Tesla valve

• F. Forster et al.; University of Washington; 1998


• Bypass-valves (TESLA-valve) as rectifier


Milestones



1993ventillose Verdrängerpu m pe

19 95Verdrän gerpum pe m itVorw ä rts - & R üc kw ärtsgang




valve less displacement pumps

bidirectional displacement pumps


Bidirectional MDP

• R. Zengerle et al; FhG-IFT, 1995

• „A bidirectional silicon micropump“

• Electrostatic actuation

• Flap valves

Change in pump direction at approx. 1000 Hz

• Phase shift between movement of flap-valve and membrane actuation

pu

mp

ra

te I

V [

µL

/min

]

Frequency [Hz]


Economical issues

Micropumps

• High fabrication costs

• Low production numbers

In the past

• Development of high performance micro pumps

• Applications were missing

Today

• Micropumps become more and more important due to Micro fuel cells, Medical applications (e.g. drug delivery), consumer applications

• Main pumping mechanism peristaltic pumps valves with pump effects single actuation pumps

microfuel cell



9.1 Valves

9.2 Pumps

9.3 Mixing

9.3.1 Liquid-Liquid Mixing

(9.3.2 Gas-Liquid Mixing)

9.4 Separating



What is Mixing?

• distinguish between mixing and diffusion! diffusion is a basic transport phenomena diffusion is always co-existent mixing is a (engineering) measure to “assist” diffusion

• diffusion “mixing” on molecular level

• mixing homogenization of concentrations

in liquid-volume or –flow basically:

generation of interfacial area between two phases

phase A - phase B


Challenge of Mixing in Microdomain

• laminar flow regime (Re << 2200) no turbulences no chaotic mixing

• mixing via diffusion only

• micromixer: generation interfacial area e.g. generation of multilaminar flow with thin lamellae

charchar lu

Re charchar lu

Re

© IMM, Mainz – Interdigital Mixer

15+15 lamellae

AB



9.1 Valves

9.2 Pumps

9.3 Mixing

9.3.1 Liquid-Liquid Mixing

(9.3.2 Gas-Liquid Mixing)

9.4 Separating

9.5 Useful Microfluidic Structures


Classification

types of liquid-liquid mixers

characteristic mixer properties

• characteristic mixing time

• retention time

• throughput

• mixing-ratio


Optimum Characteristics Depend on Application!

reactive micromixing

• mixing time relevant yield, by-products, …

• retention time important = time for reaction

• micro process engineering

dilution of substance

• mixing time less relevant(adds to overall process time)

• retention time less relevant

• high homogeneity desired

• analytical applications(lab-on-a-chip)

www.wikipedia.com


Reactive Micromixing

• mixing of two reactants chemical reaction

• synthesis of product

two consecutive processes:

1. generation of homogeneous mixture time critical step (macroscopic time scales) large interfacial area to enhance diffusion

2. mixing / reacting on molecular level depends on reaction kinetics (kAB)

]B][A[]AB[

ABkt

]B][A[

]AB[ABkt

D

ltD

2

D

ltD

2

www.wikipedia.com


Throughput of Micromixers

• usually: pressure-driven flow (PDF)

• law of Hagen-Poisseuille volume flow IV

reduced throughputin microchannels!

Numbering-Up Concept

• many micromixers in parallel

• microchannel with diameter 1/N

N 4 channels in parallelto achieve same throughput!

=

=!

4

16

l

d

l

AIV

42

l

d

l

AIV

42

VI16VI

2

dd


The Numbering-Up Concept

• higher throughput: more mixing elements same conditions in single mixer

• faster / more reliable step fromlab-scale to industrial production

• but: distribution channels required flow-splitting of single feed-stream

• uniformity problem highest flow rate in channel with smallest

flow resistance (cp. electric network) non-uniformity of resistances

- fabrication tolerances- flow patterns in flow splitter- backpressures caused by air pockets, …

different conditions in mixers

mixers ….

© IMM, Mainz


Examples of Micromixers

• many different micromixers and mixing-principles exist!

• here: typical examples for the different classes of micromixers

• “best mixer” depends on the requirements of the application!

1

2

3

4

Batch: mixing of discrete volumeContinuous: in-flow mixing

Active: external energy inputPassive: no external energy input


1. Active Batch Micromixer

surface Acoustic Waves (SAW)

• piezoelectric material (RF filters in cell-phones)

• electric actuation modes of elastic energy

• propagate at the surface of a solid body(“nano-earthquake”)

www.advalytix.de


1. Active Batch Micromixer

• mixing chamber SAW on one side-wall generation of micro-”turbulences”

mixing!

• advantage: no moving partswww.advalytix.de


2. Passive Batch Micromixer

• every microfluidic chamber acts as a passive batch micromixer mixing via diffusion only slow

• example: droplet-based microfluidics droplet movement by

electrowetting-effect two droplets of different

liquids are merged additional movement of merged

droplet to assist (“slow”) diffusion still a passive micromixer?

www.ee.duke.edu/research/microfluidics/

More on droplet-based microfluidicsin summer-semester SS12 lecture:

„Microfluidic Platforms“

More on droplet-based microfluidicsin summer-semester SS12 lecture:

„Microfluidic Platforms“


3. Active Continuous Micromixer

pulsed mixing:

• two piezoelectric micropumps (ch1 & ch2)

• Y-shaped connection of channels

• switching between the two pumps serial segmentation

K. Sugano et al.Proc. of IEEE MEMS 2006,pp. 546-549, 2006.

serial segmentation

ch1

ch1ch2

ch2


3. Active Continuous Micromixer

pulsed mixing:

• two piezoelectric micropumps (ch1 & ch2)

• Y-shaped connection of channels

• switching between the two pumps serial segmentation

• expansion after junction thin vertical lamellae (taylor dispersion)

• application: production of gold nanoparticles

Au particles

K. Sugano et al.Proc. of IEEE MEMS 2006,pp. 546-549, 2006.

micropump

switch

micropump

ch1

ch2


Interdigital Mixer

4. Passive Continuous Micromixer

see also chapter 4: Diffusion

advection Principles

• hydrodynamic actuated

• example: Dean mixer

multilamination Principles

• generation of thin phase-lamella

• example: Split and Recombine

• example: Interdigital mixer

Advection Multilamination

Micro-channel

down-scaled diffusion length

Split and Recombine

Dean-Mixer

© IMTEK


Continuous & Batch: Mixing in Droplet

continuous generation of droplets

• injection of two miscible phases (w1 & w2) into single droplet immersed in immiscible phase (oil)

• mixing within droplet (batch) along channel(bended channel parts induce stretch and fold streams)

oil

sw2

w1H. Song, M.R. Bringer, J.D. Tice,C.J. Gerdts, R.F. IsmagilovApplied Physics Letters, 83(22),pp. 4664-466, 2003.



• defined start of mixing within the droplet separating stream (s) separates the two phases prior contact position along channel corresponds to mixing time

investigation of reaction kinetics in ms time-scale

oil

sw2w1



• examples: dosing of reagents

FeCl3

(NH4)(SCN)

Fe(SCN)3


The Centrifugal Micromixer

mixing in rotating microchannels

• pumping via rotation:centrifugal force F moves liquid through radial channels

• two liquids A & B are injected intoseparate reservoirs under rotation injection of liquids A & B

mixing productrotating disk

mixing channel

liquid collectionon stationary

receiving vessel

© IMTEK – MEMS Applications



mixing is induced by the “Coriolis-Stirring” effect

• transversal Coriolis force FC on flowing liquid (velocity u)

• most pronounced in centre of the channel

• advection due deflection of transversal liquid movement

transversaladvection (“stirring”)




mixing Performance

• micromixedness ratio = measure for mixing

• high mixing quality at veryhigh volume throughput!

fluid A

fluid B

“Coriolis-Stirring”along channel


Split and Recombine Mixer


Mixing of Immiscible Liquids

• emulsion = mixture of two immiscible liquid phases every mixer can also be used to mix immiscible liquids the resulting emulsion has a certain droplet-size distribution micromixers can generate very monodisperse emulsions

(i.e. narrow size-distribution of droplets)

• example: emulsification in out-off-planeInterdigital Micromixer (IMM)

IMM Mainz

“out-of-plane” multilamination

V. Haverkamp, W. Ehrfeld, K. Gebauer,V. Hessel, H. Löwe, R. Richter, C. Wille,Fresenius J. Anal. Chem., 364,pp. 617-624, 1999.


Emulsification in Interdigital Micromixer

two immiscible phases:Silicon-oil & water

critical parameters on droplet-size:

1. smaller droplets athigher volume flow

2. smaller droplets athigher flow-rate ratio increased flow rate of

stationary phase

3. smaller droplets atsmaller channel widths

300 ml/h

600 ml/h

1200 ml/h

1:1 7:1 35:1

40 µm 20 µm

operation of miccro fluid

Documents

mf effects

high flow

valveless

fixed geometry

effects amp

flow rate

pump chamber

moving parts9