1. Introduction to Microfluidic Devices
ME 381R Lecture 21
Introduction to Microfluidic Devices
Dr. Andrew Miner
Nanocoolers, Inc.
Austin, TX 78735

2. Outline Microchannels Valves Pumps Microfluidic Thermal Systems
Sensors
Extracting, Mixing, Separation, Filtering

3. Microchannels Variety of shapes and manufacturing techniques,
depending on application.
Typically laminar due to very small length scales
and flow rates. From Evans et al. [2]:

4. Microchannels
So here are the SEM images. Singe 40X100 um and 40 40X100 multi- channel design. The features are here.

5. Microchannels (Garimella and Singhal, Heat Transfer Engineering, 25, p
So here are the SEM images. Singe 40X100 um and 40 40X100 multi- channel design. The features are here.

6. Microchannels (Garimella and Singhal, Heat Transfer Engineering, 25, p
So here are the SEM images. Singe 40X100 um and 40 40X100 multi- channel design. The features are here.

7. Passive Valves

8. Active Valves Pneumatic valve: Thermopneumatic valve:
Pressure pushes
silicone diaphragm
against inlet/outlet.
(Shown closed)
Thermopneumatic valve:
Bubble pushes silicone
diaphragm against inlet/outlet.
(Shown closed)

9. Active Valves Thermal expansion actuated:
Asymmetric thermal expansion of resistors closes valve boss against outlet.
(Shown open)

10. Pumps
Membrane pump:
- Can also be powered by piezoelectric or thermal effects
- Unsteady flow rate

11. Pumps Diffuser pump operation:
- Based on different pressure loss coefficients of
diffuser and nozzle sections
- Powered by membrane
or bubble pumps
- Unsteady flow rate

12. Pumps Bubble pump: - Typically needs check valve to operate as desired
- Unsteady flow rate

13. Bubble Jets (for ink jet printers)
Bubble pump forcefully ejects ink when expanding
then draws ink from reservoir when collapsing.

14. Permanent Magnet, DC Conduction Pump (DCCP)
High Heat Flux Cooling
Pumps
Classification of Electromagnetic Pumps (MFD)
After Baker and Tessier, '87
Permanent Magnet, DC Conduction Pump (DCCP)
Lyon, et. al., '50

15. NC-A, Permanent Magnet Direct Current Conduction Pump
High Heat Flux Cooling
Pumps
NC-A, Permanent Magnet Direct Current Conduction Pump
NC-A EOP Centrifugal
Vol (cm3)
Max. Eff. (%)
R. Drack, '03
S. Yao, et. al., '03

16. Liquid Metal Cooling System
High Heat Flux Cooling
Pumps
Liquid Metal Cooling System
Notebook Computer

17. High Heat Flux Cooling Heat Transfer
Theoretical Basis, Laminar and Turbulent Flow in a Tube, Constant Wall Heat Rate U
Laminar Flow q
Turbulent Flow in High and Moderate Pr Fluids: Dittus-Boelter
Turbulent Flow in Low Pr Fluids: Sleicher-Rouse
G. W. Dittus and L. M. D. Boelter, University of Califronia Publications in Engineering 2, 443 (1930)
C. A. Sleicher and M. W. Rouse, International Journal of Heat and Mass Transfer 18, 677 (1975)

18. High Heat Flux Cooling Heat Transfer
Turbulent Flow Enhancement of Heat Transfer
Laminar Flow, All Pr
Radial Diffusive HT, Axial Convective HT
Turbulent Flow, High and Moderate Pr
Radial Convective HT, Axial Convective HT
Turbulent Flow, Low Pr
Radial Diffusive HT, Axial Convection HT
Low Pr Turbulent Flow: Thermally Laminar, Hydrodynamically Turbulent!!

19. Microchannel Heat Exchanger Cooling System (Cooligy)
Here is the system layout of Prof Goodson’s project. We can see that the whole system was on one chip and there are several important components like the macro scale heat exchanger system. They are Micro channels in the evaporator region which sits on the chip, heat source; Condenser region and electrokinetic pump providing the driving force of the fluidic medium. Let’s talk about the EK pump first. EK pump controls flow by electrical potential across a porous medium, which generates a force that induces the liquid to flow. The electroosmotic flow (EOF) is generated in the charge double layer that forms in the first few nanometers of the liquid/dielectric interface. Solvated ions move under the influence of an applied external field, carrying the bulk liquid by viscous drag. The electroosmotically-driven flow rate, QEOF, is directly proportional to the applied voltage and the zeta potential of the porous pump medium. The maximum pressure generated, PMAX, is inversely proportional to the square of the pump medium's pore diameter. Therefore, by optimizing the pump medium's pore size and zeta potential, and controlling the applied voltage.
There is a company from Sandia lab research group focus on EK pump application. The animation can help us understand the physical phenomena behind that.
Cooligy,

20. Sensors Drag Flow Sensor: Differential Pressure Flow Sensor:
PIEZORESISTOR
STRAIN GAUGE
Drag Flow Sensor:
Flow measured by strain
gauge.
Differential Pressure Flow Sensor:
Flow measured by pressure difference.

21. Macro/Micro Mixing Study (Brenebjerg, et al., 1994 [3])
In “macro” channels (100 mm long x 300 m wide x 600 m deep):
Good mixing was observed – caused by turbulence from sharp corners.
In “micro” channels (5 mm long x 180 m wide x 25 m deep):
Very little mixing observed – mixing by diffusion only, with no turbulence.

22. Diffusion-Based Extractor
Molecules with large
diffusion coefficients
can be extracted from
those with small
diffusion coefficients.

23. Active Mixer (Evans et al., 1997, [2])
Bubble pumps and one-way bubble
valves mix fluid using chaotic
advection to increase surface area
between mixing fluids.
Mixing chamber is 600 m wide x
1500 m long x 100 m deep.
Entire system manufactured on a
single silicon substrate. IN
OUT

24. Mixing and Separation (Lin and Tsai, 2002 [5])
This system mixes two liquids and separates out
any gas bubbles.

25. Mixing and Filtering (Lin and Tsai, 2002 [5])
Mixing effect of bubble
pump cycles (5, 50, 100,
150, 200 Hz, respectively)
Gas bubble filter – Surface
energy of a gas bubble is less
for a wider channel.

26. Fluidic Logic
In 1950’s, there was a push research in this area for control
systems resistant to radiation, temperature, and shock.
Examples of fluidic logic components:

27. Microfluidic Logic Integration (Quake et al., 2002 [7])
High-density integration of fluidic logic, analogous to electronic ICs.

28. Microdialysis Microneedle
Filtering capability built in to
needle wall.

29. Microneedle Features Smallest traditional needles:
- 305 m OD, 153 m ID (30-gauge)
- Only available with straight shafts, no interior features
Microneedles:
- Almost any size and shape (defined lithographically)
- Can incorporate microfilters for excluding large molecules
- Reduced insertion pain for patient
- Reduced tissue damage
- Capable of targeting a specific insertion depth
- Capable of very low flow rates, but limited in higher flow
rate applications

30. Hypodermic Injection Microneedles

31. Device for Continuous Sampling (Zahn et al., 2001, [6])
Microdialysis needle filters larger molecules (proteins) to
prevent inaccuracies and reduced sensor life span.
Sensors and entire fluidic system are located on a single chip.
Three fluids used: 1) sampled fluid from needle, 2) saline to
clean the sensor, and 3) glucose to recalibrate the sensor.
Device can be worn by patient, and coupled with a similar
device for drug delivery. For example, glucose monitor
coupled with insulin injector for diabetic patients.
Sensor uses an enzyme to catalyze a reaction with glucose,
resulting in H2O2 oxidizing to a Pt electrode, creating a voltage.

32. Device for Continuous Sampling (Zahn et al., 2001, [6])

33. References
Kovacs, Gregory T.A., Micromachined Transducers Sourcebook, WCB/McGraw-Hill, 1998.
Evans, J., Liepmann, D., and Pisano, A.P., “Planar Laminar Mixer,” Proceedings of the IEEE 10th Annual Workshop of MEMS (MEMS ’97), Nagoya, Japan, Jan , 1997, pp
Branebjerg, J., Fabius, B., and Gravensen, P., “Application of Miniature Analyzers from Microfluidic Components to TAS,” van den Berg, A., and Bergveld, P. [eds.], Proceedings of Micro Total Analysis Systems Conference, Twente, Netherlands, Nov , 1994, pp
Not used
Lin, L, and Tsai, J., “Active Microfluidic Mixer and Gas Bubble Filter Driven by Thermal Bubble Micropump,” Sensors and Actuators, Vol. A 97-98, pp , 2002.
Zahn, J.D., Deshmukh, A.A., Papavasiliou, A.P., Pisano, A.P., and Liepmann, D., “An Integrated Microfluidic Device for the Continuous Sampling and Analysis of Biological Fluids,” Proceedings of ASME International Mechanical Engineering Congress and Exposition, Nov , 2001, New York, NY.
Quake, S.R., Thorsen, T., Maerkl, S.J., “Microfluidic Large-Scale Integration,” Science, Vol. 298, pp , Oct. 18, 2002.
Intel Corporation, product information from web site (
Goodson, K.E., 2001, “Two-Phase Microchannel Heat Sinks for an Electrokinetic VLSI Chip Cooling System,” 17th IEEE SEMI-THER Symposium.
Eksigent Technologies, LLC, information for EK pump from web site (
A. Miner, U. Ghoshal, “Cooling of High Power Density Micro-Devices using
Liquid Metal Coolants," Applied Physics Letters, Vol. 85, pp
Cooligy Inc.,
Nanocoolers, Inc.