ELECTRO OSMOTIC PUMPS

1
ELECTRO OSMOTIC PUMPS

• ME-595 TERM PROJECT
• M. EMRE BASARAN

2
Outlines

• Electro osmotic pumps
• Application areas
• Governing equations
• Electro-osmotic pump types
• Concluding remarks

3
Features of electro-osmotic pumps

• Involves no moving parts
• Moves fluid by the application of an electric
  field through electro-osmosis mechanism
• Only field induced flow design that can move low
  conductivity fluids
• Pressure Flow rate range are typically greater
  than that of other designs

4
Comparison with other micro pumps
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Physical Aspects

• Dimensions Geometry
• Typical widths of the channels are 5-100 mm
• Rectangular, circular or irregular cross
  sections
• Fluid Properties
• Low and high conductivity fluids can be used.
• Newtonian and non-Newtonian fluids (blood)
• Different viscosity and densities used
• Usually requires a electrolyte buffer solution

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Physical Aspects

• Applied voltages
• For portable systems DC, otherwise AC power
  used. (up to 10 kV range)
• Ohmic heating
• Occurs at high currencies.
• Generates bubbles, destroy biological samples
• Its an upper limit for the systems.
• .

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Application Areas

• Generally used in micro total analysis systems
  (mMTAS)
• Drug Delivery,
• Sample analysis, Separation and mixing
  processes.
• Also used in micro-processor cooling systems

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EOF Mechanism Governing Equations

• Surface Reactions
• Electric Double Layer (EDL)
• Momentum Equation
• Velocity profiles
• Max. flow rate (Qmax)
• Max. Pressure (Pmax)

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Surface Reactions

• Surfaces charge when contact with liquid
• SiOH OH-? SiO- H2O
• SiOH H ? SiOH2
• PH value determines the surface charge
• In EOF most common reaction is deprotonation of
  the surface
• Surface becomes negatively charged

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Electric Double Layer

• Positive ions adsorbed by inner layer. Theyre
  immobile.
• Diffuse layer consists of mostly positive ions
• Diffuse layer is mobile and positive ions have
  neutral H2O molecules around them.

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Electric Double Layer

• Zeta potential is the value of the wall potential
  at the shear plane. This is the effective
  potential for the diffuse layer.
• Net charge density given as

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Momentum Equation

• A steady, laminar, constant density flow in a
  channel is given as
• 
  (1)
• In EOF the body force (f) is the applied electric
  field force (E) and the density is the net charge
  density (rE)
• 
  (2)

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Momentum Equations

• Momentum equation becomes
• 
  (3)
• Assumptions
• Channel is long and straight
• Electro double layer has a finite width
• Cross section of the channel is constant along
  the flow direction
• The applied electric field is uniform and along
  the x axis of the channel
• The potential at the wall is constant and uniform
• Debye-length much smaller than the capillary
  radius

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Helmutz-Smoluchowski velocity (uEO)

• 
  (3)
• where Electro-osmotic mobility

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EOF velocity with back-pressure

(4)
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Max flow-rate and pressure

• Maximum flow rate is achieved when there is no
  back pressure
• (5)
• Maximum pressure is achieved when there is no
  flow in the channel
• ? (6)

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Effects of the channel dimensions
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Types of the electro-osmotic pumps

• Cascade pumps
• Planar (shallow) pumps
• Porous electro-osmotic pumps

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Low voltage cascade pump

• Low voltage consumption (10 V )
• Suitable for on chip applications
• Single stage
• Pmax281 (Pa)
• 15 stage
• Pmax-154200 (Pa)
• Qmax34.6 (nl/min)

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Low voltage cascade pump

• Narrow channels work as high pressure pump
• Wide channel works in opposite direction as a low
  pressure pump
• Disadvantages
• Low flow rate
• Electrode span life

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Planar Electro-osmotic pumps

• Large flow area for high flow rates and shallow
  depth for high back pressure capacity
• Pressure Range0.1-5 (atm)
• Flow rate range 10-20 mm/min

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Planar Electro-osmotic pumps

• Disadvantages
• Requires high voltages(1-5 kV), therefore they
  are not portable and suitable for on chip
  applications
• Wide and shallow channels requires high
  structural stability

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Porous type electro-osmotic pumps

• Whole frit surface becomes charged
• Fluid flows through the tiny irregular channels
  of the frit
• High flow rates (0.8-1 ml/min)
• High backpressure range (1-5 atm)

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Porous type electro-osmotic pumps

• Pump dimensions are not suitable for on chip
  applications
• High voltage consumption, not portable
• Suitable for microchip cooling applications

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CONCLUDING REMARKS

• Among the given pump types, cascade pumps are
  the most promising because of their low voltage
  consumption.
• Most of the Micro systems require on chip
  applications. So more research should be done on
  low voltage portable systems.
• Structural stability is one of the key factors in
  planar type pumps, so new manufacturing
  techniques should be observed.
• Porous type pumps are good for microchip cooling
  systems, yet theyre not portable.

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THANKS
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References

• Alarie, J.P., et al. (2001), Electroosmotically
  Induced Hydraulic Pumping on Microchips, Oak
  Ridge National Laboratory, Oak Ridge.
• Brask, A., (2003), Principles of Electroosmotic
  Pumps, Tecnical University of Denmark
  Mikroelektronik Centret, Master Thesis c961052.
• Brask, A., Goranovic Bruus, H., (2003),
  Theoretical analysis of the low-voltage cascade
  electro-osmotic pump, Sensors and Actuators B
  Chemical, Volume 92, Issues 1-2 (July) 127-132
• Chen, C.H. Santiago, J.G., (2002) A Planar
  Electroosmotic Micropump, Journal of
  Microelectromechanical Systems, Vol. 11, No. 6,
  (December), 672-683.
• Goranovic, G., (2003), Electrohydrodynamic
  aspects of two-fluid microfluidic systemstheory
  and simulation, Tecnical University of Denmark
  Mikroelektronik Centret, Ph.D. Thesis PhD no.
  000699.
• Selvaganapathy, P.,et al., Buble Free
  Electrokinetic actuation, submitted to Journal of
  MicroElectroMechanical Systems (in press)
• Sharp, K.V., et al. (2001), Liquid Flows in
  Microchanells, in The MEMS Handbook, M.
  Gad-el-Hak, Ed., CRC Press, London etc..
• Takamura, Y., et al. in Brask, A., (2001),
  Principles of Electroosmotic Pumps, Tecnical
  University of Denmark Mikroelektronik Centret,
  Master Thesis c961052(2003).
• Thopasridharan, M., Parnham, C., Yeary, L.,
  Electroosmotic Pump, 16 October 2004,
  lthttp//www.cep.tntech.edu/mems/Electroosmotic20P
  ump.pdfgt
• Yao, S., Huber, D., Mikkelsen, J.C. Santiago,
  J.G., (2001), A Large Flowrate Electroosmotic
  Pump with Micron Pores, 2001 ASME International
  Mechanical Engineering Congress and Exposition,
  November 11-16, 2001 New York, NY.
• Zeng,S., et al. (2002), Electroosmotic flow pumps
  with polymer frits, Sensors and Actuators B
  Chemical, Volume 82, Issues 2-3, (February),
  209-212.