Transcript Motivati on Energy and Nanotechnology Gang Chen Rohsenow Heat and Mass Transfer Laboratory Mechanical Engineering Department Massachusetts Institute of Technology Cambridge, MA 02139

Motivati
on
Energy and Nanotechnology
Gang Chen
Rohsenow Heat and Mass Transfer Laboratory
Mechanical Engineering Department
Massachusetts Institute of Technology
Cambridge, MA 02139
Sources
http://www.sc.doe.gov
Nano for Energy
• Increased surface area
• Interface and size effects
Molecules
L = 1-100 nm
l=1 nm
L---Mean
free path
l---wavelength
Electrons
L=10-100 nm
l=10-50 nm
Photons
L > 10 nm
l=0.1-10 mm
Phonons
L=10-100 nm
l=1 nm
Nanoscience Research for Energy Needs
• Catalysis by nanoscale materials
• Using interfaces to manipulate energy
carriers
• Linking structures and function at the
nanoscale
• Assembly and architecture of
nanoscale structures
• Theory, modeling, and simulation for
energy nanosciences
• Scalable synthesis methods
National Nanotechnology Initiative Grand Challenge Workshop, March, 2004
Examples
Grätzel cell for photovoltaic
generation and water splitting
• Radiation transport to maximize
absorption
• Two phase flow
• Electrochemical transport
• Multiscale, multiphysics transport
Catalytic nanostructured
hydrogen storage materials
•
•
•
•
•
Mass transport
Heat transfer (intake and release)
Small scale thermodynamics
Two phase flow
Multiscale and multiphysics
Thermoelectrics Devices
I
I
I
N
P
Diffusion
Hot Side
Cold Side
Power Generation
Figure of Merit:
Electrical
Conductivity
ZT =
Seebeck
Coefficient
2
S T
ke  kp
Electron
Phonon
Thermal Conductivity
COLD SIDE
HOT SIDE
• Refrigeration
• Power Generation:
T(hot)=500 C, T (cold)=50 C
ZT=1, Efficiency = 8 %
ZT=3, Efficiency =17 %
ZT=5, Efficiency =22 %
• Critical Challenges:
Reduce phonon heat conduction while
maintaining or enhancing electron transport
Nanoscale Effects for Thermoelectrics
Interfaces that Scatter Phonons but not Electrons
Electrons
L=10-100 nm
l=10-50 nm
Phonons
L=10-100 nm
l=1 nm
Electron
Molecular Dynamics (Freund)
Phonon
State-of-the-Art in Thermoelectrics
FIGURE OF MERIT (ZT)
max
3.0
PbTe/PbSeTe Nano
PbSeTe/PbTe
Quantum-dot
Superlattices
(Lincoln Lab)
S2 (mW/cmK2)
k (W/mK)
ZT (T=300K)
AgPbmSbTe2+m
(Kanatzadis)
Bi2Te3/Sb2Te3
Superlattices
(RTI)
1.5
1.0
28
2.5
0.3
Harman et al., Science (2003)
2.5
2.0
32
0.6
1.6
Bulk
Bi2Te3 alloy
PbTe alloy
0.5
Skutterudites
(Fleurial)
Si0.8Ge0.2 alloy
Dresselhaus
0.0
1940
1960
1980
YEAR
2000
2020
Bi2Te3/Sb2Te3 Nano
Bulk
S2 (mW/cmK2)
k (W/mK)
ZT (T=300K)
50.9
1.45
1.0
40
0.6
2.4
Venkatasubramanian et al.,
Nature, 2002.
Potential Applications
Transportation
Mechanical losses
9kJ
Exhaust
Gasoline
100 kJ
Gasoline
100kJ10kJ
Mechanical losses
10kJ
9kJ
30kJ
30kJ
6kJ
10kJ
35kJ
35kJ
6kJ
Driving
Driving
Auxiliary
Auxiliary
10kJ
Parasitic
heat losses Coolant
Parasitic
heat losses Coolant
Oil or
Oil or
Nat’l Gas
Nat’l Gas
Exhaust
Exhaust
Entropy
Entropy
Losses
Thermal
Heating
Thermal
PowerPower Heating
TPV & TE Recovery
Refrigeration
Refrigeration
& &
Electrical
Electrical
Power Power
Appliances
Appliances
Electricity
PV
In US,
transportation
uses ~26% of
total energy.
10% energy
conversion
efficiency
= 26% increase
in useful energy
Residential
In US, residential
and commercial
buildings consume
~35% energy supply
Challenges and Opportunities
• Mass production of nanomaterials
• Energy systems: high heat flux
• Nanomaterials are trans-boundary
• Basic energy research leads to
breakthroughs
• Transports (molecular, continuum)
are crucial
• Inter-departmental collaborations