Microscale Ionic Wind For Local Cooling Enhancement

PowerPoint PresentationNanoscale Transport
Research Group
Microscale Ionic Wind For Local Microscale Ionic Wind For Local Cooling EnhancementCooling Enhancement
Birck Nanotechnology Seminar SeriesBirck Nanotechnology Seminar Series
David B. GoDavid B. Go Ph.D. CandidatePh.D. Candidate
October 11October 11thth, 2007, 2007
D. B. Go, 10/11/2007, Slide 2 Nanoscale Transport Research Group
OutlineOutline • Introduction
• Experimental – macroscale – microscale
• Modeling – continuum-scale – sub-continuum
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1970 1975 1980 1985 1990 1995 2000 2005 2010 Year
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/c m
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/c m
components/skin/size
R. Cavin (2004)
“Search for radically new methods of heat removal is one of the most critical research
directions” – V. Zhirnov, SRC
Present Electronics Cooling TechnologiesPresent Electronics Cooling Technologies natural convection cooled motor drive
Rockwell Automation, http://www.ab.com/drives/160z/
heat pipe, heat sink and fan cooled laptop http://en.wikipedia.org/wiki/Image:AMD_heatsink_and_fan.jpg
http://www.intel.com/support/processors/ mobile/pm/sb/cs-007971.htm
Current Research ActivitiesCurrent Research Activities • Variety of cooling technologies being investigated
– heat spreader/TIM → CNT thermal interfaces [Cola et al. (2007)]
– closed loop liquid cooling → micropumps [Singhal & Garimella (2007)]
– compression refrigeration → vapor compression [Nnanna (2005)]
– solid-state refrigeration → thermoelectrics [Wang & Bar-Cohen (2007)]
– air cooling enhancement → microscale ionic winds
What is an Ionic Wind?What is an Ionic Wind? • Air ions pulled by an electric field collide with neutral air
molecules causing motion → ionic wind
• Ionic winds can be generated in a stagnant atmosphere or in the presence of a bulk flow → secondary wind
• Ions are generated through collisions between electrons and neutral molecules → electron impact
www.sharperimage.com
Creating an Ionic WindCreating an Ionic Wind • Macroscale ionic wind generated via corona discharge
– large potential between sharp and blunt electrodes – naturally occurring, free electrons accelerated towards sharp
electrode → electron impact ionization – air ions pulled to the blunt electrode
e
e
e
e
e
Microscale Ionization Microscale Ionization -- PaschenPaschen’’s Curves Curve
• Analytical prediction of breakdown of air → Paschen’s curve
• Experiments in microgaps deviate from Paschen’s curve → breakdown voltage decreases
• Particle simulations confirmed electron injection → field emission
Advantages of scaling down to the microscale (~10 μm): • lower operating voltages for practical applications (~100 V) • minimal volume impact on thermal solution
Zhang et al. (2004)
Ionic Winds Ionic Winds -- HistoryHistory • Seminal Work
– first observed by Hauksbee (1719) and quantified by Chattock (1899) – first rigorous studies by Steutzer (1959) and Robinson (1961)
• External Flow Applications – dc surface corona discharges [Soetomo (1992), Leger et al. (2002), Artan et
al. (2002)] – ac plasma actuators [Roth et al. (1998,2000), Jacob et al. (2004), Huang et
al. (2006)]
• Heat Transfer Applications – enhanced natural convection [Marco & Velkoff (1963), Kibler & Carter
(1974), Owsenek et al. (1995)] – enhanced internal flow [Nelson et al. (1998)], heat exchangers
[Wangnipparnto et al. (2002)], external flow [Velkoff & Godfrey (1979)]
• Miniaturization – ionic wind driven pumps [Schlitz et al. (2003,2004), Jewell-Larsen (2004)] – field emission ionization [Zhang et al. (2004), Peterson et al. (2005)] – microfabricated electrodes [Hsu et al. (2007)]
Ionic Winds for Cooling EnhancementIonic Winds for Cooling Enhancement • Ionic winds in the presence of a bulk flow distort the boundary
layer → air cooling can be enhanced at the wall • Ionic wind engines can be integrated on the backside of a chip,
onto a spreader or skin of a notebook → hot spot cooling
emitted electrons
eeee e
ionized air
wind
wind
~10μm
infrared camera infrared camera
Macroscale Experiment Macroscale Experiment –– Corona VisualizationCorona Visualization
co lle
ct in
g el
ec tr
od e
co lle
ct in
g el
ec tr
od e
Macroscale Results Macroscale Results –– Principal IR ImagesPrincipal IR Images
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bulk flow + corona: i = 15.0 μA; Φ = 4.51 kV
co lle
ct in
g el
ec tro
de co
lle ct
in g
el ec
tro de
Ionic winds produced 5-25°C cooling using < 100 mW power D. B. Go, R. A. Maturana, T. S. Fisher, S. V. Garimella, Int. J. Heat Mass Trans. – in review
Macroscale Results Macroscale Results –– Heat Transfer AnalysisHeat Transfer Analysis
• Apply energy balance → heat transfer coefficient (h)
• Analytically determine heat transfer relationship
( )airplate TThAq −=
1 4
ionich i∝
heat transfer coefficient can be used to quantify cooling enhancement
based on kinetic energy added to fluid by ion/neutral collisions
amount of heat removed
Macroscale Results Macroscale Results –– Local Local hh
distance from plate leading edge, x (mm)
lo ca
lh ea
tt ra
ns fe
rc oe
ffi ci
en te
nh an
ce m
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(b)
(a)
(c)
(d)
(e)
(a) i = 15 μA; 4.51 kV (b) i = 12.5 μA; 4.39 kV (c) i = 9 μA; 4.13 kV (d) i = 6 μA; 3.85 kV (e) i = 3 μA; 3.53 kV
Ionic wind enhances cooling > 200%
Macroscale Results Macroscale Results –– Analytical RelationshipAnalytical Relationship
fourth root of current, i1/4 (μA1/4)
io ni
c w
in d
he at
tra ns
fe rc
oe ffi
ci en
10
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downstream
upstream
1 4
ionich i∝
Microwave Source
– desired mechanical properties → electrode robustness
Highly Graphitic Polycrystalline Diamond (HGPD) Maschmann et al. (2006)
Peterson et al. (2005) image courtesy R. A. Maturana
Microwave Plasma CVD
Miniature Wind Tunnel
Continuum Governing EquationsContinuum Governing Equations
0u∇ ⋅ = r r
( ) 2u u p u fρ ν⋅∇ = −∇ + ∇ + rr rr r r
( ) 2 pc u T k Tρ ⋅∇ = ∇
rr
r r r
Energy Body Force
- Coulombic force ions exert on bulk flow
Navier-Stokes Electrostatic
The governing equations solved sequentially using user- defined functions in FLUENT
D. B. Go, S. V. Garimella, T. S. Fisher, R. K. Mongia, J. Appl. Phys.(2007)
0.8
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o f h
ea t t
simulation experiment
Model captures major heat transfer trends
Continuum Modeling Continuum Modeling -- InsightInsight
distance from plate leading edge, x (m)
ex te
nt in
to flo
w do
m ai
n, y
0.001
0.002
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0.004
0.005
0.006
0.007 0.26 0.24 0.22 0.20 0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00
Figure 8 (a)
ex te
nt in
to flo
w do
m ai
n, y
0.001
0.002
0.003
0.004
0.005
0.006
0.007 0.26 0.24 0.22 0.20 0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00
(b)
ex te
nt in
to flo
w do
m ai
n, y
0.002
0.004
0.006
0.008
0.010
(b)
ex te
nt in
to flo
w do
m ai
n, y
0.002
0.004
0.006
0.008
0.010
SubSub--Continuum ModelingContinuum Modeling
• Direct Simulation Monte Carlo (DSMC) – particle simulator based on work by Zhang et al. (2004) – provides understanding of the physics of field emission-generated
ionization – local body force resolution based on ion/neutral collisions →
import into continuum model
Direct Simulation Monte CarloDirect Simulation Monte Carlo
cathodeanode (1)
(2)
(3)
(4)
(1) electron is emitted from the cathode and is accelerated toward the anode → Fowler-Nordheim equation
(2) electron collides with neutral molecule → statistically generate ions (3) original and newly liberated electron are accelerated toward the anode (4) generated ion is accelerated towards the cathode → ion/neutral
collisions generate body force
dielectric plate
DSMC Sample SimulationDSMC Sample Simulation
• animation of 10 ps simulation electron
N2 ion
O2 ion
DSMC Sample SimulationDSMC Sample Simulation
• animation of 10 ps simulation electron
N2 ion
O2 ion
DSMC Model BenchmarkingDSMC Model Benchmarking • Predict Townsend’s first ionization coefficient → number of ionization
events per unit length • Compared to experimental and simulations literature
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80 90 100 110 120 130 140 150 160 170
Present Work
ratio of electric field to pressure, E/P (V cm-1 mmHg-1)
ra tio
present work
DSMC Model DSMC Model –– Physical LimitsPhysical Limits
applied potential, Φ (V)
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35 0.5 μA 5 μA 10 μA 15 μA 25 μA
0 25 50 75 100 125 0
0.02
0.04
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0.1
D. B. Go, S. V. Garimella, T. S. Fisher in preparation
DSMC suggests a physical limit to ion initiation
electron kinetic energy (eV)
0.5
1
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2
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2 2
e X e X (elastic)
e X 2e X (ionize X
)
− −
− − +
− −
+ → +
+ → +
+ → +
Ionization cross-sections suggest ion initiation at 20 V → why the discrepancy?
DSMC Model DSMC Model –– Physical Limits (2)Physical Limits (2)
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excitation
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SummarySummary • Ionic winds for electronics cooling
– experimental results indicate significant cooling possible
• Microscale ionic wind engines – nanoscale features for improved operation and robustness – heat transfer experiments
• Continuum simulations – comparison to results shed insight onto nature of heat transfer
enhancement
• Sub-continuum simulations – provide insight into physical limits and impact of boundary – multi-scale simulation
AcknowledgementsAcknowledgements • Advisors
• Undergraduate research fellow – Raul A. Maturana
• Colleagues and fellow graduate students – Dan Schlitz, Ph.D. – Wei Zhang, Ph.D. – Vaibhav Bahadur – Ratnakar Karru – Vishal Mahulkar – NSTRG & CTRC & members of Prof. Peroulis’ group
• Intel Corporation for financial support
Question 1Question 1
DSMC Model DSMC Model –– Physical Limits (2)Physical Limits (2)
5
10
15
20
25
30
35
excitation
0.2
0.4
0.6
0.8
1
Microwave Source
– desired mechanical properties → electrode robustness
Highly Graphitic Polycrystalline Diamond (HGPD) Maschmann et al. (2006)
Peterson et al. (2005) image courtesy R. A. Maturana
Microwave Plasma CVD
Miniature Wind Tunnel
Microscale Ionic Wind For Local Cooling EnhancementBirck Nanotechnology Seminar Series
Outline
Creating an Ionic Wind
Ionic Winds - History
Outline
Macroscale Results – Local h
Macroscale Results – Analytical Relationship
Outline
Summary
Acknowledgements
Question 2
Question 3
Question 4

Microscale Ionic Wind For Local Cooling Enhancement

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