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

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

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]:

Microchannels

Microchannels (Garimella and Singhal, Heat Transfer Engineering, 25, p. 15, 2004)

Passive Valves

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

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

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

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

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

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

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

NC-AEOP Centrifugal Vol (cm 3 ) Max. Eff. (%) ● R. Drack, '03 ● S. Yao, et. al., '03 NC-A, Permanent Magnet Direct Current Conduction Pump High Heat Flux Cooling Pumps

Liquid Metal Cooling System Notebook Computer High Heat Flux Cooling Pumps

Turbulent Flow in High and Moderate Pr Fluids: Dittus-Boelter Turbulent Flow in Low Pr Fluids: Sleicher- Rouse Laminar Flow ● 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) Heat Transfer Theoretical Basis, Laminar and Turbulent Flow in a Tube, Constant Wall Heat Rate U q 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!! High Heat Flux Cooling

Microchannel Heat Exchanger Cooling System (Cooligy) Cooligy,

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

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.

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

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. OUT IN

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

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.

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:

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

Microdialysis Microneedle Filtering capability built in to needle wall.

Microneedle Features Smallest traditional needles:  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

Hypodermic Injection Microneedles

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 H 2 O 2 oxidizing to a Pt electrode, creating a voltage.

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

References Kovacs, Gregory T.A., Micromachined Transducers Sourcebook, WCB/McGraw-Hill, Evans, J., Liepmann, D., and Pisano, A.P., “Planar Laminar Mixer,” Proceedings of the IEEE 10 th 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 , 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 2001 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, Intel Corporation, product information from web site ( Goodson, K.E., 2001, “Two-Phase Microchannel Heat Sinks for an Electrokinetic VLSI Chip Cooling System,” 17 th 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.