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Flow in Microfluidic Devices

Year 4 project talk presentation
by

Syeda Shah

on 30 June 2011

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Transcript of Flow in Microfluidic Devices

Flow in Microfluidic Devices
Microelectronics:
telecommunications
internet technology
other complex miniaturized systems
Microfluidics:
DNA analysis
cell manipulation
mixing
portable integrated miniature diagnostic kits
Medical
Anti-terrorism
Environmental
Animal care
LOC Devices
(Lab-On-Chip)
Components:
pumps
valves
mixers
reactors
dispenser
separator
sensors
Schematic cross-section of the LoC system for DNA research currently under development
...interconnected by microchannels...
integrated system composed of the pump,
the filter and channels
integrated components:
regulate
mix
manipulate
separate
detect the samples
Syeda Shah
4th Year projects
Microfluidics
Microfluidics: Study of fluid transport at micrometer scales
allow the potential capabilities of a conventional laboratory to be confined into a chip
Flow in Microchannels
Flow in Pipe
Flow in Microchannels
EDL
Electric Double Layer
Electro-Kinetic Effects
Microchannels
Summary
Electro-osmosis
Streaming Potential
Electrophoresis
Sedimentation Potential
Slit Microchannels
Cylinderical microchannels
Rectangular microchannels
Sector Microchannel
Electro-kinetic effects: the phenomena observed due
to the presence of the Electric Double Layer (EDL)
near the solid-liquid interface
Liquid motion is induced by
an external electric-field
liquid flows over a stationary charged surface
excess counterions in the diffuse layer of the EDL move under the applied electrical field
causes the ions in the EDL to move towards one electrode
gives rise to a body force on the liquid setting the liquid in motion
pressure-driven flow where the velocity is parabolic
electro-osmotic flow has constant velocity over the cross section
In compact layer, the velocity profile is not flat but it is negligibly small
Liquid set into motion by a pressure gradient in the absence of an electric-field
counterions in the diffuse
layer of the EDL
accumulate downstream,
carrying the surrounding liquid with them
result in a electric current in the pressure driven flow direction
The build up of electric field gives rise to a Conduction Current which opposes
the Streaming Current
Streaming potential
pressure drop measured across the capillary
particle motion induced by the electric field over a stationary liquid
the application of an external electric field to a solid, liquid or gas particle in a bulk liquid phase
potential difference generated as charged
particles settle or rise through a fluid by an
application of an applied force
Each of the particles in the liquid are surrounded by an atmosphere of opposite charges
The particles move in a stationary liquid between 2 electrodes, embracing a new atmosphere and leaving behind the old one.
Poisson Eqn
Poisson Boltzmann Eqn
Fluid Mechanics
dimensionless
Debye Huckel Parameter
linearize
The inverse of k is the characteristic thickness of the Electric Double Layer.
K separation distance or the
ratio of the channel's height
to the EDL thickness
Electrokinetics in Microfluidics
by Dongqing Li (2004)
A large K either means that there is a large separation distance between the two plates or the EDL thickness is very small since
K is the ratio of the channels height to the EDL thickness.
Solutions for slit Microchannel
Linearized
Exact
Poisson's Eqn in 1D
Linearized Poisson Boltzmann Eqn
Fourier Analysis
Boundary Conditions for rectangular microchannel
(non-homogeneous)
Numerical Solution
For large Psi, linear approximation not valid
Can use finite-difference method to approximate solutions to Differential Eqn
plots of the EDL potential field, against the non-dimensional height and width of the rectangular channel for a square microchannel.
increasing the value of K, confines the EDL potential field to near the surface of the rectangular microchannel.
for small K, there are significant effects at the corners
Electro-osmotic flow in sector microchannels
by Chien C Chang et al (2009)
Electrokinetics in Microfluidics
by Dongqing Li (2004)
Theta = 1/4pi
K=1
K=10
Theta = 3/4pi
At microscales, we have to take into consideration the effects of the EDL field
Project has explored the electrokinetic phenomena involved in microchannels with particular emphasis being placed on the electro-osmotic
The effect of the EDL potential field has been considered while varying the non-dimensional Debye-Huckel parameter.
Results have indicated that there are signicant effects on corners, for both rectangular and sector channels.
At low values of K, the EDL region is large
and has a signicant eect on the corners.
Transient Electro-osmotic flow
Channel Cross-sections
Further work:
Full transcript