Direct Energy Conversion (1.3 Mb)

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–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