energy and nanotechnology
TRANSCRIPT
Motivation
Energy and Nanotechnology
Gang Chen
Rohsenow Heat and Mass Transfer LaboratoryMechanical Engineering Department
Massachusetts Institute of TechnologyCambridge, MA 02139
Sources
http://www.sc.doe.gov
Nano for Energy
Photonsnm=0.1-10 m
Phonons=10-100 nm
=1 nm
Electrons=10-100 nm=10-50 nm
---Mean free path
---wavelength
Moleculesnm
=1 nm
• Increased surface area• Interface and size effects
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
Catalytic nanostructuredhydrogen storage materials
• Radiation transport to maximize absorption
• Two phase flow• Electrochemical transport • Multiscale, multiphysics transport
• Mass transport• Heat transfer (intake and release)• Small scale thermodynamics• Two phase flow• Multiscale and multiphysics
Thermoelectrics Devices
Media Clip
COLD SIDE
HOT SIDE
Power Generation
I N P
I I
Cold Side
Hot Side
Dif
fusi
on
Figure of Merit:
2
e p
S TZT
k k
Thermal Conductivity
ElectricalConductivity
SeebeckCoefficient
• Critical Challenges:Reduce phonon heat conduction while
maintaining or enhancing electron transport
Electron Phonon
• Power Generation: T(hot)=500 C, T (cold)=50 C
ZT=1, Efficiency = 8 %
ZT=3, Efficiency =17 %
ZT=5, Efficiency =22 %
• Refrigeration
Nanoscale Effects for Thermoelectrics
Phonons=10-100 nm
=1 nm
Electrons=10-100 nm=10-50 nm
Electron Phonon
Interfaces that Scatter Phonons but not Electrons
Molecular Dynamics (Freund)
State-of-the-Art in Thermoelectrics
PbTe/PbSeTe
S2 (W/cmK2) 32 28k (W/mK) 0.6 2.5 ZT (T=300K) 1.6 0.3
BulkNano
Harman et al., Science (2003)
Bi2Te3/Sb2Te3
S2 (W/cmK2) 40 50.9k (W/mK) 0.6 1.45 ZT (T=300K) 2.4 1.0
BulkNano
Venkatasubramanian et al., Nature, 2002.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1940 1960 1980 2000 2020
FIG
UR
E O
F M
ER
IT (
ZT
) max
YEAR
Bi2Te3 alloy
PbTe alloy
Si0.8Ge0.2 alloy
Skutterudites(Fleurial)
PbSeTe/PbTeQuantum-dotSuperlattices(Lincoln Lab)
Bi2Te3/Sb2Te3
Superlattices(RTI)
AgPbmSbTe2+m
(Kanatzadis)
Dresselhaus
Gasoline100 kJ
10kJ 30kJ 35kJ
Parasiticheat losses Coolant Exhaust
9kJ10kJ
6kJAuxiliary
Driving
Mechanical losses
Coolant
Exhaust
Gasoline100kJ
10kJ
30kJ 35kJ
9kJ10kJ
6kJAuxiliary
Driving
Mechanical losses
Parasiticheat losses Exhaust
10% energy conversion efficiency = 26% increase in useful energy
In US, transportation uses ~26% of total energy.
Heating
Refrigeration &Appliances
TPV & TE Recovery
PVElectricity
Oil orNat’l Gas
EntropyThermal Power
Electrical Power
Heating
Refrigeration &Appliances
Losses
Electricity
Oil orNat’l Gas
Entropy
Thermal Power
Electrical Power
Potential ApplicationsTransportation
In US, residential and commercial buildings consume ~35% energy supply
Residential
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