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ELECTRO OSMOTIC
PUMPS
ME-595 TERM PROJECT
M. EMRE BASARAN
Outlines
 Electro osmotic pumps
 Application areas
 Governing equations
 Electro-osmotic pump types
 Concluding remarks
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
Comparison with other micro pumps
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
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
It’s an upper limit for the systems.
.
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
EOF Mechanism &
Governing Equations
 Surface Reactions
 Electric Double Layer (EDL)
 Momentum Equation
 Velocity profiles
 Max. flow rate (Qmax)
 Max. Pressure (Pmax)
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
Electric Double Layer
 Positive ions adsorbed
by inner layer. They’re
immobile.
 Diffuse layer consists of
mostly positive ions
 Diffuse layer is mobile
and positive ions have
neutral H2O molecules
around them.
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.
2
 Net charge density given as:  E   
Momentum Equation
 A steady, laminar, constant density flow in a
channel is given as:
0  p  m2u  f
(1)
 In EOF the body force (f) is the applied
electric field force (E) and the density is the
net charge density (E)
 f =  E E    E
2
(2)
Momentum Equations
 Momentum equation becomes:

 E  p
 u 

m  m

2
(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
Helmutz-Smoluchowski velocity (uEO):
uEO
where  EO  

m
 da

  EO E X
m dx
Electro-osmotic mobility
(3)
EOF velocity with back-pressure
u  r   uEO  uPois   EO EX
dp  a

dx
2
 r2 
4m
(4)
Max flow-rate and pressure
 Maximum flow rate is achieved when there is
no back pressure
Qmax   EO EX A
(5)
 Maximum pressure is achieved when there is
no flow in the channel
Q   u  dA  0
A
→
8  m A
P 
a2
(6)
Effects of the channel dimensions
Types of the electro-osmotic pumps
 Cascade pumps
 Planar (shallow) pumps
 Porous electro-osmotic pumps
Low voltage cascade pump
 Low voltage




consumption (10 V )
Suitable for on chip
applications
Single stage
Pmax=281 (Pa)
15 stage
Pmax-15=4200 (Pa)
Qmax=34.6 (nl/min)
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
Planar Electro-osmotic pumps
 Large flow area for high flow rates and shallow depth for high
back pressure capacity
 Pressure Range:0.1-5 (atm)
 Flow rate range: 10-20 mm/min
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
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)
Porous type electro-osmotic pumps
 Pump dimensions are
not suitable for on chip
applications
 High voltage
consumption, not
portable
 Suitable for microchip
cooling applications
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 they’re not portable.
THANKS
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., Goranović & 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.
Goranović, G., (2003), Electrohydrodynamic aspects of two-fluid microfluidic systems:theory 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,
<http://www.cep.tntech.edu/mems/Electroosmotic%20Pump.pdf>
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 1116, 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.
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