–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT.
Direct Energy Conversion. Gang Chen. Mechanical Engineering Department.
Direct Energy Conversion Gang Chen Mechanical Engineering Department Massachusetts Institute of Technology Office: Room 3-260 Tel: 617-253-0006 Email:
[email protected] URL: http://web.mit.edu/nanoengineering
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Direct Thermal-to-Electric Energy Conversion Technologies
Thermionic Converter
Thermoelectric Converter
Thermophotovoltaic Converter
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Thermionic Power Generation EXTERNAL LOAD
Ta
Tc
• Electron Distribution is f(E) ~ exp(-E/kBT)
e
CATHODE
E Ec
ANODE
E Ea
• Ec, Ea are working functions at cathode and anode • Only electrons with energy larger than working function or barrier height can flow from one electrode to another
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Performance of Thermionic Converters
Hatsopoulos and Kaye, JAP, 1958
USSR TOPAZ
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Challenges and Opportunities • • • • •
Space charge effects Reliability Low work function materials Small gap devices Field-emission enhancement
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
4
10
2
EMISSIVE POWER (W/cm µm)
Photovoltaic Cells
Filter
Heat Source
THERMOPHOTOVOLTAICS Useful Useless
3
10
2
5600 K
10
2800 K
1
10
1500 K 0
10
800 K
10
-1
0
• • • • •
2
EG
4 6 WAVELENGTH (µm)
8
10
Frequency Selective Emitter Frequency Selective Filters Photon Recycling Structures Evanescent Wave Structures High Efficiency PV Cells
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Potential Performance
Experimentally Demonstrated ~ 18%
Badalsaro et al., JAP, 89, 3319 (2001)
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Challenges and Opportunities • Spectral control –
Selective emitters – Selective reflectors – Selective filters
• High efficiency cells • Thermal management • Near-field devices –WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Photonic Crystal Selective Emitter Alternating layers of tungsten and alumina
Si substrate
A. Narayanaswamy and G. Chen, PRB 70,125101, 2004 –WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Near Field Energy Conversion 89
1.2 10
Wavelength (µm) 8.75 8.5 8.25
8
SiC Source (BN, SiC) PV material 3
Power absorbed (Wcm-2)
10
2
10
101
Power absorbed
7
8 10
d = 1 nm d = 0 nm d = 10 nm
4 107
Blackbody
0 0.14
100 10-1 0
Flux (Wm-2eV-1)
d = 5 nm
100 200 Vacuum gap (nm)
0.145 0.15 0.155 Frequency (eV)
0.16
300 –WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Near-Field Effect on Efficiency
Laroche et al., JAP, 100, 063704 (2006) –WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Radioisotope Powered Thermoelectric Generators 10 Earth orbit (Transit, Nimbus, LES) 7 planetary (Pioneer, Voyager, Galileo, Ulysses, Cassini) 6 on lunar surface (Apollo ALESEP) 4 on Mars surface (Viking 1& 2) 3 RHUs on Mars Pathfinder
Voyager 2 (1977)
Radioisotope Missions
Voyager 1 (1977)
Ulysses (1990)
Apollo 11 (1969) Apollo ALSEP (1969-1972)
Cassini (1997)
Pioneer 11 (1973)
Transit 4 A (1961) LES 9 (1975)
Transit 4 B (1961)
LES 8 (1976)
Transit 5BN-1 (1963)
Transit Triad-01-0X Nimbus 3 (1972)
Galileo (1989)
Transit 5BN-2 (1961)
(1969)
Viking 1 & 2 (1975) Mars Pathfinder (1996) (RHU’s only)
Pioneer 10 (1972)
GPHS Radioisotope Thermoelectric Generator –WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Thermoelectric Power Generation HOT SIDE COLD SIDE
I
I
N
I
+
P
COLD SIDE
HOT SIDE
Figure of Merit: Electrical Conductivity
Seebeck Coefficient
σS2T ZT = k Thermal Conductivity –WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
ZT DILEMMA Methods of Reducing k In Bulk Materials:
INSULATOR SEMICONDUCTOR SEMIMETAL METAL
S
ZT
σ
• Alloy, 1950s (Ioffe) • Rattlers, 1990 (Slack)
k
σS2T ZT = k
Wanted: Phonon Glass / Electron Crystal
square array of Pn (not to scale) T
vacant
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
State-of-the-Art in Thermoelectrics
FIGURE OF MERIT (ZT)
max
3.0
PbSeTe/PbTe Quantum-dot Superlattices (Lincoln Lab)
AgPbmSbTe2+m (Kanatzadis)
2.5 2.0 1.5 1.0
Bi2Te3/Se2Te3 Superlattices (RTI) Bi2Te3 alloy PbTe alloy
0.5 0.0 1940
Si0.8Ge0.2 alloy 1960
1980
Skutterudites (Fleurial)
Dresselhaus 2000
2020
YEAR –WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Nanocomposites Approach – Increase interfacial scattering by mixing nano-sized particles. – Enable low-cost, large scale application.
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Nanocomposite Synthesis
50 nm
Si
Ge
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Electron Transport Over Potential Barriers
5 nm
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Thermal Conductivity of Si0.8Ge0.2
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Challenges and Opportunities • Further improving ZT • System and device developments
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Comparison of Technologies 0.6 POWER GENERATION EFFICIENCY
ZT CARNOT CYCLE
0.5
m
10
Power Plant
7
0.4
4 THERMAL THERMAL POWER POWER PLANT PLANT
0.3
2 STIRLING STIRLING GENERATOR GENERATOR 1
0.2 THERMIONIC GENERATORS
0.1 0
Diesel Plant
TPV 0.5
IC Engine
AUTOMOTIVE ENGINES
Thermionic Converter
Thermoelectric THERMOELECTRIC Converter POWER GENERATORS 1
2 3 4 5 6 TEMPERATURE RATIO (T hot /T cold )
7
8 9 10
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
Potential Applications in Nuclear Power Generation • In combination with mechanical power generation • Combinations of direct conversion technologies for high efficiency
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
ACKNOWLEDGMENTS • Current Members
• Collaborators (partial list)
H. Asegun (Molecular Dynamics) V. Berube (hydrogen storage) J.W. Gao (nanofluids) S. Goh (nanowires and polymers) T. Harris (Thermoelectrics&Nanomaterials) Q. Hao (Thermoelectrics) D. Kramer (Solar thermoelectrics) H. Lee (Thermoelectric Materials) H. Lu (TPV and PV) A. Minnich (thermoelectrics) A. Muto (nanowires and thermoelectrics) A. Schmidt (ps pump-and-probe) S. Shen (near field transfer) Dr. M. Chieso (nanofluids) Dr. X. Chen (optics, Pump-and-Probe)
Sponsors: DTRA, DOE, NASA, NSF, ONR, Ford, Seagate, and others
M.S. & G. Dresselhaus (MIT, NW&CNT, Theory) J.-P. Fleurial (JPL, Thermoelectric Devices) J. Joannopoulos (MIT, Photonic Crystals) Z.F. Ren (BC, Thermoelectric Materials, CNT) X. Zhang (Berkeley, Metamaterials)
• Past Members (Partial List) Prof. A. Narayanaswamy (Columbia Univ) Dr. Zony Chen (McKinsey) Prof. C. Dames (Nanowires, UC Riverside) Prof. D. Borca-Tasciuc (Nanowires, RPI) Prof. T. Borca-Tasciuc (Thermoelectrics,RPI) Dr. F. Hashemi (Nano-Device Fabrication) Dr. A. Jacquot (TE Device Fabrication) Dr. M.S. Jeng (Nanocomposites, ITRI) Dr. R. Kumar (Thermoelectric Device Modeling) Dr. W.L. Liu (superlattice) Dr. D. Song (TE and Monte Carlo, Intel) Dr. S.G. Volz (MD, Ecole Centrale de Paris) Prof. B. Yang (TE and Phonons, U. Maryland) Prof. R.G. Yang (Nanocomposites, U. Colorado) Prof. D.-J. Yao (TE Devices, Tsinghua Univ.) Prof. T. Zeng (Thermionics, NCSU)
–WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT
