osmotic pump delivery system

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

Features of electro-osmotic pumps::

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:

Comparison with other micro pumps

Physical Aspects:

Physical Aspects Dimensions & Geometry Typical widths of the channels are 5-100 m m 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:

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:

Application Areas Generally used in micro total analysis systems ( m MTAS): Drug Delivery, Sample analysis, Separation and mixing processes. Also used in micro-processor cooling systems

EOF Mechanism & Governing Equations:

EOF Mechanism & Governing Equations Surface Reactions Electric Double Layer (EDL) Momentum Equation Velocity profiles Max. flow rate (Q max ) Max. Pressure (P max )

Surface Reactions:

Surface Reactions Surfaces charge when contact with liquid SiOH + OH - → SiO - + H 2 O SiOH + H + → SiOH 2 + PH value determines the surface charge In EOF most common reaction is deprotonation of the surface Surface becomes negatively charged

Electric Double Layer:

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 H 2 O molecules around them.

Electric Double Layer:

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:

Momentum Equation:

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 ( r E ) (2)

Momentum Equations:

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 th a n the capillary radius

Helmutz-Smoluchowski velocity (uEO)::

Helmutz-Smoluchowski velocity (u EO ): (3) where Electro-osmotic mobility

EOF velocity with back-pressure:

EOF velocity with back-pressure (4)

Max flow-rate and pressure:

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)

Effects of the channel dimensions:

Effects of the channel dimensions

Types of the electro-osmotic pumps:

Types of the electro-osmotic pumps Cascade pumps Planar (shallow) pumps Porous electro-osmotic pumps

Low voltage cascade pump:

Low voltage cascade pump Low voltage consumption (10 V ) Suitable for on chip applications Single stage P max =281 (Pa) 15 stage P max-15 =4200 (Pa) Q max =34.6 (nl/min)

Low voltage cascade pump:

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:

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 m m/min

Planar Electro-osmotic pumps:

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:

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:

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.




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 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.

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