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WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORYNanoEngineering GroupNanoEngineering Group

ENERGY NANOTECHNOLOGY--- A Few Examples

Gang Chen

Nanoengineering GroupRohsenow Heat and Mass Transfer Laboratory

Massachusetts Institute of Technology

Cambridge, MA 02139

Email: [email protected]://web.mit.edu/nanoengineering


Thermal-Electrical Energy ConversionTemperature (K)

Grand Challenges: Efficiency and cost effective mass production

500 1000 1500 2000 25005000 5500 6000

EFFI

CIE

NC

Y

0

0.2

0.4

0.6

0.8

1

0

2

4

6

8

100 50 100 150 200 250 300

CO

EFFI

CIE

NT

OF

PER

FOR

MA

NC

E

REFRIGERATION POWER GENERATION

THERMODYNAMIC LIMIT

Power Plant

Auto Solar PV

Thermo-PV

Thermoelectrics

HouseholdRefrigerator

EnvironmentallyBenign Refrigeration

Energy EfficiencyWaste Heat Recovery

RenewableEnergy


Nano for Energy• Increased surface area• Interface and size effects

PhotonsΛ > 10 nm

λ=0.1-10 µm

PhononsΛ=10-100 nm

λ=1 nm

ElectronsΛ=10-100 nmλ=10-50 nm

Λ---Mean free path

λ---wavelength

MoleculesΛ = 1−100 nm

λ=1 nm

• Thermodynamics• Kinetics


Phonon and Electron Engineering for

Thermoelectric Materials


Thermoelectric Devices

COLD SIDE

HOT SIDE

-

I

+

N P

HOT SIDE

COLD SIDE

Nondimensional Figure of Merit

kTSZT

2σ=

Reverse Heat Leakage Through Heat Conduction

Joule Heating

Seebeck Coeff.Electron Cooling

GPHS Radioisotope Thermoelectric Generator


0

0.5

1

1.5

2

2.5

3

3.5

4

1940 1960 1980 2000 2020YEAR

FIG

UR

E O

F M

ERIT

(ZT)

max

Bi2Te3 alloy

PbTe alloy

Si0.8Ge0.2 alloy

PbTe/PbSeTeS2σ (µW/cmK2) 32 28k (W/mK) 0.6 2.5 ZT (T=300K) 1.6 0.3

BulkNano

Harman et al., Science, 2003

Bi2Te3/Sb2Te3

S2σ (µW/cmK2) 40 50.9k (W/mK) 0.6 1.45 ZT (T=300K) 2.4 1.0

BulkNano

Venkatasubramanian et al., Nature, 2002.

Skutterudites(Fleurial)

PbSeTe/PbTeQuantum-dotSuperlattices(Lincoln Lab)

Bi2Te3/Sb2Te3Superlattices(RTI)

Dresselhaus

State-of-the-Art in Thermoelectrics

(MichiganState)


Heat Conduction Mechanisms

A New Crystal? Inhomogeneous Multilayers?

Uni

t Cel

l of S

uper

latt

ice

Unit Cell of B Layer

Lay

er B

Lay

er A


0

20

40

60

80

10 1 10 2 10 3 10 4

THER

MA

L C

ON

DU

CTI

VITY

(W/m

K)

LAYER THICKNESS (Å)

BULK

SPECULAR (p=1)

p=0.95

p=0.8DIFFUSE (p=0)

Yao (1987)Yu et al. (1995)0

20

40

60

80

10 1 10 2 10 3 10 40

20

40

60

80

0

20

40

60

80

10 1 10 2 10 3 10 410 1 10 2 10 3 10 4

THER

MA

L C

ON

DU

CTI

VITY

(W/m

K)

LAYER THICKNESS (Å)

BULK

SPECULAR (p=1)

p=0.95

p=0.8DIFFUSE (p=0)

Yao (1987)Yu et al. (1995)

Heat Conduction Mechanisms in Superlattices

Coherent Structures Are Not Necessary, Nor Optimal!

Major Conclusions:

• Ideal superlattices do not cut off all phonons due to pass-bands

• Individual interface reflection is more effective

• Diffuse phonon interface scattering is crucial

10-1

100

101 102 103

Capinski et al. 1999Capinski et al. 1999

Yao 1987 Yu et al. 1995

Nor

mal

ized

The

rmal

Con

duct

ivity

Period Thickness (Å)

T=300KAlAs/GaAs

In-Plane

Cross-Plane

LD

LD

Ideal Superlattices

In-Plane

Cros

s-Pl

ane


Photon Engineering:Thermophovoltaics


ThermophotovoltaicsH

eat S

ourc

e

Phot

ovol

taic

Ce l

ls

Filte

r

• Frequency Selective Emitter• Frequency Selective Filters• Photon Recycling Structures• Evanescent Wave Structures• High Efficiency PV Cells

10-1

100

101

102

103

104

0 2 4 6 8 10

EMIS

SIVE

PO

WER

(W/c

m2 µm

)WAVELENGTH (µm)

5600 K

2800 K

1500 K

800 K

EG

UselessUseful


ω Free Space

kx

SurfaceModes Energy density in the vicinity of a

half-plane of BN.High Energy Density, Monochromatic EM Fields Exists Near Surfaces

When ε is Equal but of Opposite Signs. But They Are Non-Emitting!

Surface Plasmons and Surface Phonon Polaritons

10-5

10-3

10-1

101

103

105

0.1 0.2 0.3 0.4 0.5 0.6

5 10 15 20 25

Energy (eV)

Ene

rgy

Den

sity

(Jm

-3eV

-1)

Wavelength (µm)

d = 10 nm

d = 100 nm

d = 1 µm

d = 10 mm

blackbody

Surface Waves and Near Surface Energy Density


Near Field Energy Conversion

10-1

100

101

102

103

0 100 200 300

Pow

er a

bsor

bed

(Wcm

-2)

Vacuum gap (nm)

Power absorbed

Blackbody

0

4 107

8 107

1.2 108

0.14 0.145 0.15 0.155 0.16

88.258.58.759

Flux

(Wm

-2eV

-1)

Frequency (eV)

Wavelength (µm)

d = 0 nmd = 1 nm

d = 5 nm

d = 10 nmSource (BN, SiC) PV material

SiC


Coupled Conduction and RadiationNonequilibrium Thermoelectric Devices


Nonequilibrium Transport

Battery

Proposed Nonequilibrium Thermoelectric Devices

Explore nonequilibrium between electrons and phonons couple the cooling target with thermoelectric element without direct lattice contact

pe kkTSZT

+=

2σX

CoolingTarget

T1

Electron Temperature, Te

Phonon Temperature, Tp

VacuumGap

Battery

T2

Conventional Micro TE Cooler

T1

Electron Temperature

Phonon TemperatureCooling

TargetThermoelectric Element

T2

Conventional TE Cooler

T1Cooling Target Thermoelectric Element

Battery

T2


Surface Waves

Far-Field

d

Three orders of magnitude increase in energy transfer flux due to surface plasmon resonance

Nanoscalegap

Macroscale gap

d=10 nm

Model Based on Fluctuation-Dissipation Theorem

Surface Plasmon Coupling of Electrons

T1

T1


ke/k=0.1Z=0.002K-1

TH=300K

120

140

160

180

200

220

240

260

100 101 102 103 104

THERMOELECTRIC ELEMENT LENGTH (µm)

CO

LD E

ND

TEM

PER

ATU

RE

(K)

G=108 W/(m3K)G=1010 W/(m3K)G=1012 W/(m3K)Conventional

Surface-Plasmon Enabled NonequilibriumThermoelectric Refrigerators

• Performance is determined by the doping concentration and operation temperature.• Principle works for both refrigerators and power generators.

0

0.2

0.4

0.6

0.8

1

1 10 100THERMOELECTRIC ELEMENT LENGTH (µm)

CO

P

G = 108 W/(m3 K)G = 1010 W/(m3 K)G = 1012 W/(m3 K)Conventional

ke/k = 0.1Z = 0.002K-1

TH = 300K

Cooling Load q = 50 W/cm2

InSb

G


Key Points• Nanoscale effects are enabling breakthroughs in

energy technologies.• Need cost-effective and mass producible

nanotechnology for energy applications.• Fundamental understanding leads to new

manufacturing paradigms. • Fundamental research problems exist in both

individual nanostructures and mesoscopicnanostructures.

• Multidisciplinary research and interdisciplinary researchers are needed.


ACKNOWLEDGMENTS• Current Members

H. Asegun (Molecular Dynamics)V. Berube (hydrogen storage)Z. Chen (Metamaterials, TPV)S. Goh (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)S. Nakamura (nanowires and thermoelectrics)A. Narayanaswamy (Metamaterials, TPV)G. Radtke (hydrogen storage)A. Schmidt (ps pump-and-probe)E. Skow (polymers)S. Shen (lubrication, rarefied gas dynamics)Dr. M. Chieso (nanofluids)Dr. X. Chen (thermoelectrics, Pump-and-Probe)Dr. D. Vashee (thermoelectrics)Prof. Y.T. Kang (nanofluids)

• CollaboratorsM.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. 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)

Sponsors: ARO, DOE, NASA, NSF, ONR, Industries

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