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What is microfluidics?Microfluidics refers to fluid flow in
microchannels as well as to microfluidic
devices (pumps, valves, mixers, etc.) and systems.
One of the dimensions of flow is measured in µm:s – e.g. channel.
Microfluidics
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Why study microfluidics?»Reduction in size»Control of small amount of fluids»The reduced consumption of reagents»The capability of building integrated systems»Reduction of power consumption»Parallel devices + faster processes = high througput»Safety»Reliability»Integration + Multifunctionality »Portable devices»User friendly devices
Control of breeding and cloning (P,D)Control of breeding
and cloning (P,D)
Food qualitity, contaminations (P,D)
Food qualitity, contaminations (P,D)
GMO in food (D)GMO in food (D)
Pharmacogenomics/proteomics
Pharmacogenomics/proteomics
Mutation screening (D)Mutation screening (D)
PharmaPharma LSR/BiotechLSR/BiotechAgricultural/
Food IndustryAgricultural/
Food Industry
D = DNA arraysP = protein arrays
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4. MICROFLUIDIC PHENOMENA + MODELS
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Continuity equation
( )0, with = 1,2,3.i
i
v it x
ρρ ∂∂+ =
∂ ∂
Navier-Stokes equations
Isotropic Newtonian fluid
( ) 2 with , , = 1,2,3.
3ji i i k
j i j ijj i j i k
vv v v vpv f v i j kt x x xj x x x
ρ µ δ ∂∂ ∂ ∂ ∂∂ ∂
+ = − + + − ∂ ∂ ∂ ∂ ∂ ∂ ∂
Boundary and initial conditions
Models for fluid flow
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Questions about microfluidics models!
• Scaling?
• Continuum Assumption?
• Surface forces?
• Other issues
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Scaling
1. In fluidics, assume two round pipes with the same flow situation, same Reynolds number
Loss of pressure becomes much larger in microchannels (r small)
2. Required power
Required power becomes larger in microchannels (r small)
3. In microchannels Reynold’s number tends to be small.This implies laminarity of flow
1 12
1, = constantp C C
r∆ =
2 2
1, constantP C C
r= =
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Continuum Assumption
• In modeling fluid-flow, the actual molecular structure is replaced by a continuum.
Knudsen number characterizes for gases.Continuum hypothesis holds better for liquids than gases.In microworld continuum assumption seems to hold reasonably well. Breaks down in nanoworld. Need molecular dynamics.
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Continuum Assumption
Knudsen number characterizes gases – no such thing for liquids.
Navier-Stokes applies when:(1) When there are more than one million molecules in smallest
volume that a macroscopic change takes place.(2) The flow is not too far from thermodynamic equilibrium.
Experimental evidence somewhat contradictory. Research needed.
In microworld continuum assumption seems to hold reasonably well. Breaks down in nanoworld. Need Molecular Dynamics.
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Surface forces
• Van der Waals forces
• Electrostatic forces
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Surface forces
• A thin layer of liquid, where electrical potential separates ions
• The motion of ions affects the properties of liquid flow
• EDL important in channels with diameter<1 mmEDL=Electronic double layer
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Special phenomena in microfluidics
• Change in viscocity
• Creation of turbulent flow
• Compressability (especially in gas flow)
• Slip flow (especially in gas flow)
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• Laminar flow– Fluid particles move along smooth paths in laminas or layers
• Turbulent flow– Fluid particles move in irregular paths, somewhat similar to
the molecular momentum transfer but on a much larger scale
”MEMS will be allover, like plastic. They are vital. They will infiltrate everything,” Karen Markus- Director of the MEMS program at MCNC – Science, October 1998.
”We are approaching another revolution that will rival the Industrial Revolution of the 18th century,” Takayuki Hirano – Director of Japan’s Micromachine Center –TIME, December 1996
”We believe that MEMS will revolutionize the way people build products in the 21st century by coupling compu-tation to the physical world on a scale that has never before been possible,” Xerox Palo Alto Research Center
8. Future of MEMS
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Time, November 8, 1999
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Some books that discuss microfluidics
1. S. Fatikow, U. Rembold: Microsystem Technology and Microrobotics, Springer, 1997.
2. M. Madou: Fundamentals of Microfabrication, CRC, 1997.
3. A. Nathan and H. Baltes: Microtransducer CAD, Physical and Computational Aspects, Springer, 1999
4. B. Romanowicz: Methodology for the Modeling and Simulation of Microsystems, Kluwer, 1998.
5. S. Senturia: Microsystem design, Kluwer, 2000.6. MEMS Handbook, (Ed. M. Gad-El-Hak, Kluwer, 2002.
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Thanks
To my research staff in microsystems both
at
Helsinki University of Technology and Tampere University of Technolgy
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Issues from control point of view
Modelling, especially systemsSimulationControl of issues in microworld (actuators)
AdhesionHysteresis
Control of large (number) of really distributed systemsCommunication, Energy