*an NSF Industry/University Cooperative Research Center Suresh Garimella

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1 Electronics Cooling Laboratory (Cooling Technologies Research Center*) Suresh V. Garimella, Director CTRC Vision The CTRC addresses research and development needs of members from diverse industries and product lines in the area of high-performance heat removal from compact spaces through member-directed investigations with a product-oriented focus. *an NSF Industry/University Cooperative Research Center

2 CTRC Research Thrust Areas Microscale Cooling Microchannel heat sinks Refrigeration on a chip Microfluidic actuators Nanoscale energy conversion Compact Cooling Technologies Phase change energy storage Nonconventional heat pipes Jet impingement Thin-film evaporation Heat transfer enhancement Portables Piezo fans Heat spreaders & heat sinks Refrigeration Miniature refrigeration systems Micro/meso-scale pulsed tube refrigeration Development of Tools TCC models & database Flow visualization modules Molecular sensors Models for acoustic noise System-level modeling Exploratory Technologies MHD Microscale pumping techniques

Fluid Flow and Heat Transport in Microchannels Single and

transport Develop predictive relationships and correlations for

measurement techniques for MEMS devices Infrared μ-piv

Garimella, Sobhan, MTE, 5(4) 293-311, 21.

3 Fluid Flow and Heat Transport in Microchannels Single and two-phase flow and heat transfer Investigate microchannel transport Develop predictive relationships and correlations for single- and two-phase flow Develop novel non-intrusive measurement techniques for MEMS devices Infrared μ-piv Garimella, Sobhan, ARHT, 23. Garimella, Sobhan, MTE, 5(4) , 21. Liu, Garimella, AIAA JTHT, 18(1), 65-72, IR PIV measurement Theory - Eq.(8).25 Radial position (mm) Velocity (m/s)

Integrable Micropumps with EHD Enhancement Piezoelectric Patch Description Source of Electric Field Source of Charges Schematic Diaphragm Steady 1-D ion-drag pump Constant stationary voltage drop

4 Integrable Micropumps with EHD Enhancement Piezoelectric Patch Description Source of Electric Field Source of Charges Schematic Diaphragm Steady 1-D ion-drag pump Constant stationary voltage drop Constant charge density upstream of the pump Charge density distribution 54.7 deg Patent pending Channel Bus Bars Steady 2-D ion-drag pump Transient 2- D ion-drag pump Repulsiontype induction EHD pump Attractiontype induction EHD pump Constant stationary voltage drop in the direction of flow Traveling potential wave along one side of the pump with other side grounded Constant uniform charge density upstream of the pump Uniform charge density upstream of the pump for 1% of duration of potential wave starting from time when potential at that cross-section is highest Induction of charges due to gradual decrease in σ from side with potential wave to other side Induction of charges due to gradual increase in σ from side with potential wave to other side Charge density distribution Walls Charge cloud Positive charge cloud Negative charge cloud Positive charge cloud Negative charge cloud Singhal, Garimella, Murthy, S&A A, 113, , 24. Singhal, Garimella, IEEE TAP, 28(2), 25

Microscale Ion Driven Airflow Preliminary estimates show that heat transfer rates of 4 W/cm 2 can be achieved with this approach, rivaling conventional liquid cooling approaches Peterson, Fisher,

5 Microscale Ion Driven Airflow Preliminary estimates show that heat transfer rates of 4 W/cm 2 can be achieved with this approach, rivaling conventional liquid cooling approaches Peterson, Fisher, Garimella, Schlitz, IMECE 23 Electron Emission & Ion Creation Generatin g Region Pumping Region Patent pending Microchannels Schlitz, Garimella, Fisher, HT-FED 24 Darkfield image of single MWNT on W tip

6 Miniature Piezoelectric Fans Ultrasonic Piezoelectric Bimorph slim profile fan Advantages of Piezoelectric Fans Low power, 1-1 mw Noiseless for frequencies: - Less than 1 Hz (infrasonic) - Greater than 2 khz (ultrasonic) Lightweight, compact and inexpensive No wearing parts, long life, robust and durable Versatile configurable to different applications baffled infrasonic fans Flow in an impingement mode Resonant vibration of small piezoelectric elements generates air flow

Enhancement in h (%) First-Mode Infrasonic Fans Heat Transfer Feasibility Heat Sink Fluidic Modeling 2-D streaming model for a baffled piezoelectric fan Y(m).4.3.2.1 Piezoelectric Fan Vertical Orientation Horizontal Orientation.

Coverage Horizontal 5 1 15 Time (sec) Optimal thickness ratio: t p /t b.5 Optimal length ratio: (L 2 -L 1 )/L 3.

7 Enhancement in h (%) First-Mode Infrasonic Fans Heat Transfer Feasibility Heat Sink Fluidic Modeling 2-D streaming model for a baffled piezoelectric fan Y(m) Piezoelectric Fan Vertical Orientation Horizontal Orientation X(m) Experimental flow visualization agrees well with model Heat transfer coefficient h (W/m 2 K) Vertical, Half Coverage Vertical, Full Coverage Vertical, No Coverage Horizontal Time (sec) Optimal thickness ratio: t p /t b.5 Optimal length ratio: (L 2 -L 1 )/L 3.6 Optimal geometry depends on material properties of the beam and the patch Analytical Açıkalın, Wait, Garimella, Raman, Heat Transfer Engineering 25, 4-14, 24 Geometry Optimization Finite element Açıkalın, Raman, Garimella, JASA 114, , 23 Buermann, Raman, Garimella, IEEE CPT 22 Basak, Raman, Garimella, ASME J Vibr. Acoustics

Thin-Film Evaporation To obtain velocity field near an evaporating meniscus and thus the mass flow rate Challenges: Moving Meniscus Accumulation of gravity particles at

plane TOP PLANE 2 CENTER PLANE BOTTOM PLANE 2 CCD CAMERA 6 Bottom Plane 1 Test setup 6 Bottom Plane 2 5 5 5 5 5 y[pix] 4 3 y[pix] 4 3 y[pix] 4 3 y[pix] 4 3 y[pix] 4 3 2 2

8 Thin-Film Evaporation To obtain velocity field near an evaporating meniscus and thus the mass flow rate Challenges: Moving Meniscus Accumulation of gravity particles at the triple line and its effect on the evaporation process 6 Top Plane 2 6 TOP PLANE 1 BOTTOM PLANE 1 Top Plane 1 6 Micro-PIV Experiments in an Evaporating Meniscus Center plane TOP PLANE 2 CENTER PLANE BOTTOM PLANE 2 CCD CAMERA 6 Bottom Plane 1 Test setup 6 Bottom Plane y[pix] 4 3 y[pix] 4 3 y[pix] 4 3 y[pix] 4 3 y[pix] x[pix] x[pix] x[pix] x[pix] x[pix] Prof. Steve Wereley s assistance for these experiments is appreciated

Model of an Evaporating Meniscus 1 μm 2 W/m 2 Steel 5 μm Thin film:.35 W Meniscus: 4.

heat transfer from Thin Film Region CFD model for the Intrinsic Meniscus region Part I- thin

Temperature Measurements with FLlR s Merlin IR Camera with 4X objective (Preliminary Results)

9 Model of an Evaporating Meniscus 1 μm 2 W/m 2 Steel 5 μm Thin film:.35 W Meniscus: 4.25 W 343K Vapor Octane 1 μm 343 K Inlet Temperature Contour A simplified analytical model for heat transfer from Thin Film Region CFD model for the Intrinsic Meniscus region Part I- thin film (invisible) Thin film θ Part II-intrinsic meniscus Junction Thickness δ j Microscale Temperature Measurements with FLlR s Merlin IR Camera with 4X objective (Preliminary Results) LI1.dC dc Thin film Temperature of Back of the Foil along LI1 Wire dC Heated Foil

Y Solidification Heat Transfer Laboratory y,

5 Phase Change Energy Storage Krishnan, Murthy,

5 2 x, inches Analytical Experimental Krishnan,

Change in Foams PCM Internal or external fins.

10 Y Solidification Heat Transfer Laboratory y, inches Phase Change Energy Storage Krishnan, Murthy, Garimella, ASME JHT, 126, , s x, inches Analytical Experimental Krishnan, Garimella, IEEE CPT, 27(1), , 24 Phase Change in Foams PCM Internal or external fins.1 X Z.1 Krishnan, Garimella, Kang, IEEE CPT, 28(2), 25 _ = Cube BCC Final Geometry

without (top) and with (bottom) a growth

Simpson, Garimella, Groh, Abbaschian, ASME

11 Crystal Growth Under Microgravity Conditions Lift-off of Shuttle carrying MEPHISTO experiment Predicted velocity vectors & isotherms during crystal growth without (top) and with (bottom) a growth capillary Schematic of MEPHISTO apparatus Simpson, Garimella, Groh, Abbaschian, ASME JHT, 123(5) , 21 Simpson, Garimella, IJHMT, 43(11), , 2

Bridgman Growth in a Transparent Material

324-335, 22 Experimental photographs used

12 Bridgman Growth in a Transparent Material Simpson, Garimella, Groh, AIAA JTHT, 16(3) , 22 Experimental photographs used to resolve the front locations inside the ampoule during crystal growth Predicted thermal and velocity fields and interface locations for a 4 μm growth case Li, Garimella, Simpson, NHT B, 43, (I) , (II) , 23

Electro-Thermal Co-Design of Emerging Electronics

Electro-Thermal Co-Design of Emerging Electronics with on-chip integration of novel cooling strategies Suresh V. Garimella Cooling Technologies Research Center, an NSF I/UCRC Purdue University 1 Grand