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Energy Research for SustainabilityMatthew M F Yuen, Ph.D. (袁 銘 輝 )
Acting Vice President for Research and Development
ASPIRE FORUMTOKYO INSTITUTE OF TECHNOLOGY, 5TH JULY,
20101香港科技大學
THE HONG KONG UNIVERSITY OF SCIENCE AND TECHNOLOGY
2
Energy/Capita Consumption 2009
Source: BP Statistical Review of World Energy Consumption June 2010
3
World Primary Energy Consumption 2009Source: BP Statistical Review of World Energy Consumption June 2010
4
World Energy Projection 2030Source: EIA International Energy Outlook 2010
5
Energy/GDP Projection 2030
Energy demand 35% higher in 2030
Energy efficiency
improves by 65%
Source: ExxonMobil - Outlook for Energy – A view to 2030
6
Industrial Energy Demand
Industrial energy demand dominant: Green manufacturing
Source: ExxonMobil - Outlook for Energy – A view to 2030
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Green Manufacturing
• Manufacturing with reduced waste and pollution through innovative product and process design, including the use of new materials and supply chain.
• “Cradle to Cradle” process - reuse/recycle• Minimum damage to environment and human,
low energy consumption
Sustainability
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Green PLM - Opportunities
• Design for sustainability• New materials – recycle / reuse• Novel green processes • Efficient supply chain
New regulations – ISO 50001What is required? – INNOVATION
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Green Product Lifecycle ManagementSource: Environmental Logic
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Green PLM - Apple
• Manufacturing– Material use– Toxic substance removal– Responsible manufacturing
• Transportation– Smaller packaging
• Product use– Energy efficiency
• Recycling– Product recyclability– Apple recycling program– Responsible recycling
• Facilities– Facilities in the big picture– Energy use– Employee commuter program
Source: Apple
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Renewable Energy Investment 2008Source: Renewables Global Status Report 2009 Update
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HKUST Cases in Energy ResearchEnergy Research & Material Research
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The energy problems are…...
• People really like using electricity, and their vehicles!
• Fossil fuels are being depleted• Global warming (CO2
production )• Air pollution caused by thermal
power generation and IC engine exhaust
Fossil fuel systems are not sustainable
Turbine or IC engine
O2 Fuel
Heat
CO2
Combustion
NOx, SOxParticulates
Mechanical energy
Electric generator
Electricity
Vehicles
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Sustainable Energy Future
Two conditions must be satisfied:
Need to re-organize the entire energy system for a sustainable energy future
2. Energy must be distributed and converted with highest efficiency
1. Energy source, sink, handling and use must besustainable
Ulf Bossel – October 2005
15Sustainable Energy Future
C-free Sources:
Consumers need motion, sound, light, heat, communicationUtilization:
Renewable or nuclear power plants
H2O + CO2
H2O + CO2
e- H2
H2O
Electrolysis
H2 Fuel Cell
e-
Biomass
Methanol or Ethanol
Methanol or EthanolFuel Cell
e-
H2O
Battery
e-
C-free cycle C-neutral cycle
Hydropower, Ocean energy, Geothermal
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Case I: Direct Alcohol Fuel Cell
17
Simple molecule– Less demanding on catalyst.
Liquid at room temperature and ambient pressure.- High energy density; readily available fuel
infrastructure. Made from natural gas or
renewable resources – Low cost, sustainable.
Why alcohol?
OC
H
H
H
HC
H
H
OC
H
H
H
H
Methanol
Ethanol
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How does DAFC work?
Alcohol solution
Direct Alcohol Fuel Cell
Methanol, Ethanol
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Single cell structure
Carbon
Flow field plate
Flow field plate+-
Anode flow channel Cathode flow channel CO2 bubble
Water
H+
Alcohol
Water/AlcoholOxygen or air with water
e-
e- e-
e-
Anode diffusion layer
Anode catalyst layer
Polymer Electrolyte
Diffusion layer
Cathode diffusion layer
Cathode catalyst layer
Catalyst particle on carbon support
Load
20
Why DAFC?
The DAFC system: Simple system design (no
reformer, no humidifier) Promise of high efficiency Silent operation (no noise) Operable at room temperature
21
Applications of DAFC
Ideal for mobile applications such as laptops, cellular phones
Also of great interest to the military – to power individual soldiers’ electronics
Next generation of road vehicles Distributed power generation.
22
Technical Challenges for DAFCE
lect
rode
pot
entia
l / V
olta
ge
Anode electrode
Cathode electrodeKinetic loss(200-300 mV)
Electrode resistance
Oxygen transport(>100 mV)
Electrolyte resistance
Electrode resistance
Kinetic loss(200-400 mV)
Current density
1.2
Alcohol crossover(25-150 mV)
Catalyst development
Catalyst development
Electrode material development
Electrode material development
Membrane modification and development
OCV loss due toalcohol crossover
Rapid drop-off due to
activation losses
Linear drop-off due to ohmic losses
Mass transport lossesAlcohol transport(25-150 mV)
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Nano-catalysts Development
PtRu nano-particles (3-4 nm) on nanotubes
Pt nano-particles (2-3 nm) on nanotubes
Prabhuram, Zhao, Yang, J. Electroanalytical Chemistry, 578 (2005) 105-112.Prabhuram, Zhao, Tang, Chen, Liang, J. Physical Chemistry B, 110(2006) 5245-5252.Prabhuram, Zhao, Liang, Chen, Electrochimica Acta, 52 (2007) 2649-2656.
20 nm
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Anode Backing LayerXu, Zhao, Ye, Electrochimica Acta, 51 (2006) 5524-5531.
PEM
Cathode DL
Cathode CLAnode CL
Anode DL
25
Mathematical Modeling
Fuel
Oxide
Liquid Gas
Liquid Gas
Anode region
Cathode region
Yang, Zhao, J. Electrochemical Society 52 (2007) 6125–6140
26
( ) ( ){[ ] [ ]) (}( )c
lc l
eff effrg rgco co
g
cc
g
lo
dp s pKk s Kk sD D N
RTp p p p
RT RTd RTsµ µ∇ − − +∇ − − =∇
+ +∇∇
2
2 2
.( ) ( ) 0
/ /rl rl
lll l l l
lKk Kk g m Consumptionp ρµ ρ µ ρ
∇ ∇ =∇ − +
APR
( ) ( ) ) ~effml m m l l l m M m
l
cU c D c U U c D c N MORρρ
∇ −∇ ∇ = ∇ + ∇ − ∇ = ∇2m(
2M H Oeff m effM mem M d mem M d
Water
C MI IN D C n D C nF Fρ
= − ∇ + = − ∇ +Mem
( )w Mem lW d
l Water
I k dpN nF dy M
ρµ
= −
AFC
.interface[ (1 ) ] l
ll g lac
mu mh
ρ α∇ − = − = −
[ (1 ) ] [ ] sin 2 | |ml g l l g g g g M mixture mixture
h
fu u u u p g u uD
ρ α ρ α ρ θ∇ − +∇ = −∇ − −
0[ (1 ) ] | |g g g g l gju C u u Uα α= + − +
.ginterface[ ] gg g g
ac
mu m
hρ α∇ = =
.
interface[(1 ) ] mmg l M
ac
Nu c Nh
α∇ − = − = −
27
. interface
.ginterface
[ ]
[ (1 ) ]
l
evporationl ll l l
cc cc
vapor c o evporationgg l g
cc cc
m m mu mh h
m m m m mu mh h
ρ α
ρ α
−∇ = = =
+ − +∇ − = = =
l g mu u u= =
. interface
. interface
[(1 ) ]
[(1 ) ]
ool o
cc
evaporationvvl v
cc
Nuc N
hN N
uc Nh
α
α
∇ − = − = −
+∇ − = =
CFC
~effV V V VN C D C Evaporation rate= − ∇gU
CPR( ) ( )
[( ( ))( ) ( ( )) ]
CL
L c Lrl rl L
L L
D s
g
f s
K dp Kk s k s ms
pd
sρ ρµ µ
∇ − + −∇ =∇−
( ) {[ ( )] }gas rg gasg s
ga
K k s p mρν
∇∇ = −∇ =gU
~effO O O ON C D C ORR= − ∇
2 2 2 2gU
28
Power Density - DMFC
29
State-of-the-art performance of acid DEFC
J. Power Sources 140 (2005) 50-58
Anode: PtSn, 1.3 mg cm-2
Cathode: Pt, 1.0 mg cm-2
Membrane: Nafion 115
Maximum power density: 28 mW/cm2
30
Alkaline DEFC
Loade- e-
OH-
OH-
OH-
EtOH
CO2
Air
Exhaust gas
Anode CathodeAEM
Pt-free catalyst Better electrode kinetics Lower fuel crossover Low cost alkaline membrane Less material corrosion
o2 5 2 2 2C H OH 3O 2CO 3H O 1.145VE+ → + =
- - o2 5 2 2C H OH 12OH 2CO 9H O 12e -0.743VaE+ → + + =
- o2 23O 6H O 12e 12OH 0.401VcE−+ + → =
AnodeCathodeOverall
Ethanol:
Y.S. Li, T.S. Zhao, Z.X. Liang, J. Power Sources 187 (2009) 387–392.
31
Anion Exchange Membrane
(a) surface (b) cross section (Low resolution)
(c) cross section (High resolution)
32
Catalysts
33
Alkaline DEFC: State-of-the-art performance
0 100 200 300 400 500 600 7000.0
0.2
0.4
0.6
0.8
1.0
0
20
40
60
80
100
120
Powe
r den
sity,
(mW
cm
-2)
Temperature: 60 oC
Cell v
olta
ge, (
V)
Current density, (mA cm-2)
Current AEM-DEFC Typical PEM-DEFC
Maximum power density: 110 mW/cm2 (Acid type: 15 mW/cm2)
34
DEFC
Ethanol + Water
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Mobile Phone Battery Charger
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MP4 Player
37
Case II: High Power LED
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HP-LED for solid state lighting• Advantages:
– long operating life (>50,000 hours), – high efficiency, – high reliability, – environmental friendly, – vivid color – compact size
• LEDs form a rapidly growing segment of the global lighting market, estimated at $75 billion a year in 2008.
lower operating costs
[Multi-Year Program Plan (FY’09-FY’15) of SSL R&D, US Department of Energy, Mar. 2009]
39
Thermal Challenge in HP-LED Packages• Higher power density results in increasing
thermal challenge.• Effect of junction temperature increase
– Luminance of HB-LEDs will reduce linearly – Life will reduce exponentially– Color will shift with temperature
(N. Narendran and Y. Gu, 2005)
70 mW, 2 lm
>10 W, >100 lm
40
Heat Conduction Plays an Important Role• LEDs: generated heat is dissipated mainly by conduction at the
source, while for conventional light sources radiation is dominant.• Thermal interfaces in the conduction path are pivotal for LED
performance
Power LED
light: ~15..40%
heat loss: ~85-60%, mostly by conduction
100 W incad. lamp
light: 5%dissipated heat: 12%
IR radiation: 83%
-
41
Heat Dissipation Bottleneck: TIM and Heatsink• TIM: thermal interface material
– To reduce the thermal resistance at the interface between the heat source and the heat sink
• Improve heat convection of heat sink
Primary heat dissipation path
TIM
Au wire
InterposerHB-LED device
Heatsink
Heat slug
Heat sink
DeviceTIMAir RTIM-heatsink
RTIM
Rheat source-TIM
Air gap exists at the interface
42
Improve the Thermal Conductive Performance• Thermal resistance can be reduced with proper choice of TIM.• Conventional TIM cannot meet the thermal dissipation requirement• VACNT-TIM is promising
Heat sink
DeviceAir
Heat sink
DeviceCNT-TIM
Air
Heat sink
DeviceSilver epoxy Air
R = 107 mm2K/W R = 75 mm2K/W
R = ? mm2K/W
RTIM-heatsink
RTIM
Rheat source-TIM
43
VACNT-TIM Synthesis by Thermal CVD
44
Thermal Performance of CNT-TIM on Si Substrates• Commercial silver epoxy: 75 mm2·K/W• CNT-TIM grown with thermal CVD on Si substrates: 15 mm2·K/W• CNT-TIM grown with PECVD on Si substrates: 7 mm2·K/W
(Kai Zhang, et al, Nanotechnology, Vol.19, pp.215706, 2008)
10 nm
Heat sink
Device
45
MD Model of CNT
• Cell dimensions: 16.6Å x 16.7Å x 24.5 Å• All atoms are unconstrained.• Boundary conditions: periodic in x and y directions• Iteration time interval – 1femtosecond (fs)• Temperature: 25oC
24.5nm XY
Z
46
NEMD Simulation-Given Constant Heat Flux
AEABBR k 2/])4([1 2/12 ∆++−+=Hot region:
24.5nm XY
Z
Hot region +Cold region - kE∆ kE∆
Based on the NEMD algorithm (Ikeshoji and hafskjold, 1994)
AEABBR k 2/])4([1 2/12 ∆−+−+=Cold region:
subii vvRv −=′Velocity rescaling:
47
NEMD Simulation
The heat flux was given as follows:tS
EJ∆∆
=
where is the heat flux of the CNT, is the cross-section area of the CNT, is the simulation time step
J S t∆
The instantaneous local temperature in each region is given as follows:
∑=
=kn
iii
Bkk vm
knT
1
2
31
Where is the amount of atoms in region , is Boltzmann’s constant, andrespectively, are the mass and velocity of atoms
kn k Bk im iv
i
>∂∂<><
=ZT
J/
λ
The thermal conductivity of the CNT, , can be calculated by the Fourier law:λ
48
Temperature Profile Along the SWCNT under Tension stress (50MPa)
y = 0.8606x + 287.7
0
50
100
150
200
250
300
350
400
0 5 10 15 20 25Z (nm)
Tem
pera
ture
(K)
Temperature distributed linearly along the CNT with a temperature gradient
49
Thermal Conductivity of SWCNT under Different Conditions
• Thermal conductivity of CNT was dependent on the applied stresses.
• The thermal conductivity monotonically decreased with the stress changing from the compression to tension.
• The thermal conductivity of the CNT subjected to torsion stress decreased with the increase of torsion stress.
• The thermal conductivity of CNT was degraded by the moisture inside the tube.
50
CNT-TIM on Al Alloy Substrates• Problem of CNT-TIM on Si Substrates
– Conflict between CNT synthesis and device fabrication if CNTs are grown on backside of Si devices
• Potential Solutions 1. CNT-TIM synthesized on Si substrates and then transferred to Al alloy
heatsink: not viable2. CNT-TIM synthesized on metal foil and then sandwiched in between device
and heatsink: easy to handle3. CNT-TIM synthesized directly on Al alloy heatsink customized production
Solution 2 Solution 3
Device
Solution 1
DeviceDevice
51
Thermal Resistance Measurement
• Sample packages were designed to take into account the contact conditions as well as the bulk thermal performance of TIM.
Si
Al alloy
TIM
Heaters
Cooler
Load cell
Sample
Holes for RTDs
Pressure transducer
Copper bars
(ASTM D5470)
RTIM-heatsink
RTIM
Rheat source-TIM
52
Light Power Testing for LED• The output light power of a LED package is measured by PMS-50
analytical system with an integrating sphere.
Integrating Sphere PMS-50 analytical system
53
Thermal Performance Improvement• The thermal resistance of CNT-TIM synthesized on Al substrates
is reduced to 4 mm2K/W.• Compared with CNT-TIM on Si substrates, CNT-TIM on Al
substrates with lower resistance is achieved by better adhesion between CNTs and substrates.
53
RTIM-heatsink
RTIM
Rheat source-TIM
54
HB-LED with VACNT-TIM (CVD) on Al Alloy Substrates• 10 W LED module with 3×3 LED chip array• HB-LED with commercial TIM burnt out at input power of 3000 mA• HB-LED with VACNT-TIM provides the LED package with a better brightness
performance and survives at the input current as high as 3750 mA.
(Kai Zhang, et al, 58th ECTC, pp.1659-1663, 2008)
0
300
600
900
1200
1500
1800
0 1000 2000 3000 4000Input current (mA)
Out
put l
ight
pow
er (m
W)
Commercial TIMVACNT-TIM on heatsinkIdeal thermal management
55
HB-LED with VACNT-TIM (PECVD) on Si Substrates• VACNT-TIM > Commercial TIM• CNT quality influences the brightness
performance of HB-LED
(Kai Zhang, et al, Nanotechnology, Vol.19, pp.215706, 2008)
020406080
100120140160
0 200 400 600 800 1000Input current (mA)
Out
put l
ight
pow
er (m
W)
Commercial TIMCNT1CNT2CNT3Ideal thermal management
56
56
Application in HB-LED packages
1×1 mm2 LED chip
LED assembly
LED package
3×3 LED module
CNT-TIMThermal conductive polymer
Heatsink
(Courtesy Advanced Packaging Technology Ltd.)
57
Packaging Process in Ultrahigh Power HB-LED
Thermal conductive polymer
Put LED device on the VACNT-TIM1; put some thermal conductive polymer around the device and CNTs using a dispenser and let it cured
Put the module on a heatsink; put some thermal conductive polymer around the module and VACNT-TIM2 using a disperser and then let it cured
Synthesize VACNT-TIM on both sides
Heatsink
LED device
Thermal conductive polymer
VACNT-TIM1
Heat spreader
Heat spreader (a)
(c)
(b)VACNT-TIM2
Heat spreader
(Kai Zhang, et al, CIRP Annals-Manufacturing Technology, Vol.56, pp.245-248, 2007), (Matthew M.F. Yuen, K. Zhang, US patent 11/752,955, 2007.)(Matthew M.F. Yuen, K. Zhang, Chinese patent 200710106382.6, 2007)
58
Summary – LED Lighting• VACNT-TIM fabricated by PECVD on Al alloy substrates
– Well aligned, high density– 4 mm2·K/W, about 6% of that of commercial TIM.
• A novel heat spreader with double sided VACNT-TIM• Possible use in convection cooling • VACNT-TIM is promising for thermal management in high power
HB-LED application.
59
Energy Institute @HKUST
60
Energy Institute @ HKUST• Current Research Centers
– Center for Sustainable Energy Technology– Center for Display Research– Center for Advanced Microsystem Packaging– Finetex-HKUST R & D center– Photonics Technology Center– Building Energy Research Center – HKUST-Foshan LED-FPD Research Center
• Energy Institute anchored in School of Engineering encompassing research in: – School of Science – new materials, …– School of Business - economics, …– School of Social Science and Humanities – policy,..
Coordinated Research Program for SUSTATAINABLE Development
61
Thank you!
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