CENTER FOR NONLINEAR AND COMPLEX SYSTEMS

Como - Italy

Providing a sustainable supply of energy to the world’s population will become a major societal problem for the 21st century as fossil fuel supplies decrease and world demand increases.

Thermoelectric phenomena are expected to play an increasingly important role in meeting the energy challenge of the future.

…a newly emerging field of low-dimensional thermoelectricity, enabled by materials nanoscience and nanotechnology.

Dresselhaus et al: Adv. Mater. 2007

‘It seems there is no problem in modernphysics for which there are one recordas many false starts and as manytheories which overlook some essentialfeatures as in the problem of thethermal conductivity of non conductingcrystals’ R. E. PEIERLS

J. B. FOURIER

1808 - Attempt to explain the thermal gradient inside the earth

QUESTION:

Can one derive the Fourier law of heatconduction from dynamical equations of motion without any statistical assumptions?

Normal transport

REMARK:

Randonmnes is an essential ingredientof thermal conductivity

deterministically random systems are tacitly required by the transport theory

THE DING-A -LING MODEL

THE DING-A -LING MODEL

J. B. FOURIER

1808 - Attempt to explain the thermal gradient inside the earth

Nature, 7 june 1984

FOURIER LAW IN QUANTUM MECHANICS?

FOURIER LAW IN QUANTUM MECHANICS?

Deterministic chaos appear to be an important ingredient for Fourier law.No exponential instability in Quantum Mechanics

FOURIER LAW IN QUANTUM MECHANICS?

Deterministic chaos appear to be an important ingredient for Fourier law.No exponential instability in Quantum Mechanics

Terra Incognita

SIGNATURES OF QUANTUM CHAOS

The distribution of energy levels spacingsobeys the Wigner-Dyson surmise

RANDOM MATRIX THEORY

Lettere al Nuovo Cimento 28 (1980) 279

G. Monasterio, T. Prosen, G.C.EPL (2005)

Plane waves solutions

Dispersionrelations

Phonon band

INTERNAL TEMPERATURE PROFILE

In nonlinear systems the position of the banddepends on the temperature

p.r.l. 88, (2002)

For uniform mass distribution, thermal conduction issymmetric

All measurements showed that a higher thermalconductance was observed when heat flowedfrom the high-mass region to the low -massregion

NEGATIVE DIFFERENTIAL THERMAL CONDUCTIVITY

Volta effect: an electric potential difference is developed by the contact of two different metals at the same temperature.

A.Volta (Como)

Powerful heat. In 1822, the Estonian–German physicist Thomas Johann Seebeck discovered that if heat is applied across the junction of two wires, a current is generated.

Abram Ioffe, 1950s : doped semiconductors have large thermoelectric effect

The initial excitement about semiconductors in 1950 was due to their promise, not in electronics but in refrigeration. The discovery that semiconductors can act as efficient heat pumps led to expectations of environmentally benign solid state homerefrigerators and power generators

Here comes another talk on fundamental limits

Thermoelectricity concerns the conversion oftemperatures differencies into electrical potentialor viceversa

It can be used to perform useful electrical workor to pump heat from cold to hot place, thusperforming refrigeration

The field of thermoelectric advanced rapidly in the 1950s when the basic science of thermoelectric materials became well established, the thermoelectricmaterial Bi2Te3 was developed for commercialization, thus launching the thermoelectric industry

Thermoelectric (Peltier) refrigerators have poorefficiency compared to compressor-based refrigerators.

During this 1960–1995 period, the thermoelectric field received little attention from the worldwide scientific research community.

Nevertheless, the thermoelectric industry grew slowly and steadily, by finding niche applications:

space missionslaboratory equipmentmedical applications

where cost and energy efficiency were not as important as energy availability, reliability, predictability, and the quiet operation of equipment.

devices used for cooling, and for power generation

Voyager mission to Jupiter and Saturn, here at its launch in 1977.

Thermoelectric devices provide on board power tooperate radio signal trasmitters, on board computers,gyros and navigational systems, spectrometers and many other scientific instruments.

These power generating systems can operate unattended, maintenance free, for many years

NASA uses thermoelectric because key advantages include high reliability, small size and no noise.

Radioisotope Thermoelectric Generators (RTGs) is the only technology (so far) capable of providing electrical power for deep-space missions including:- Voyagers I and II, -Galileo, Cassini, and the New Horizons mission to Pluto .

(The RTG is the black, cylindrical finned object at lower left).

New Horizon spacecraft to Pluto

This RTG consists of hundreds of individual silicongermanium(SiGe) thermocouples arranged around graphite-encased plutonium.

One such RTG weighs about 55 kg and produces about 240 Watts of electricity at about 7% conversion efficiency

the radioisotope heat source half-life is 87 years.

Even in the harsh environment of space these thermocoupleshave accumulated more than a trillion device-hours without asingle failure.

-Key step 1990: first significant consumer product,picnic basket cooler

- Thermoelectric industry stable and growing

Thermoelectric coolers/heaters by “Amerigon“(USA)

-2 milion climate control seats in 2006

Estimate 2% reduction in fuel consumption-World market in 2010 up to 1 billion US$

The suitability of a thermoelectric material for energy conversion or electronic refrigeration is evaluated by

The ZT figure of merit

The suitability of a thermoelectric material for energy conversion or electronic refrigeration is evaluated by

The conversion efficiency is given by

In five decades the ZT of semiconductors has increased only marginally, from about 0.6 to 1

A. Majumdar Science 303, 777(2004)

A ZT value > 3 would make solid –state home refrigerators economically competitive with compressor-based refrigerators

Metals are poor thermoelectric materials because of low Seebeck coefficient and large electroniccontribution to thermal conductivity.

A ZT value > 3 would make solid –state home refrigerators economically competitive with compressor-based refrigerators

Metals are poor thermoelectric materials because of low Seebeck coefficient and large electroniccontribution to thermal conductivity.

Insulators have large Seebeck coefficient but have too few carriers which result in large electrical resistivity

A ZT value > 3 would make solid –state home refrigerators economically competitive with compressor-based refrigerators

ZT =1.5

Mass ratio

R radius of scatterers

Heterogeneous channel

If

If

and

When the number dint of internal degrees of freedoms of moving particles become large

G.C , C.Monasterio, T. Prosen, Phys. Rev. Lett. 101, 016601(2008)

ZT increases with geometrical and internaldegrees of freedom D of gas particles.

An efficient engine

M. Horvat, T. Prosen, G.C., Phys Rev. E 80, 010102 (2009)

Two things appeared almost simultaneously in the 1990s:

new ideas and new funding.

New ideas: indicate that large improvements in ZT might be possible by making an artificial material modified on a nanometer length scale. This idea, known as a ‘quantum wellsuperlattice’, has been important for inspiring nano-scaleengineering to improve ZT.

-Environmental concern about chlorofluorocarbonsused in most compression-based refrigerationtechnologies.

-Home heating, automotive exhaust, etc. generate anenormous amount of unused waste heat

- Generation of electric power from waste heat usingthermoelectrics is becoming more and more attractive(e.g. automobile exhaust and engine heat)

Modern semiconductor manufacturing techniques are under development at two recent startups: -Nextreme (US), a spin-off from the Research Triangle Institute utilizing a superlattice technology - Micropelt (Germany), a spin-off from an Infineon/Fraunhofer Institute collaboration utilizing a wafer-scale device fabrication method .

Both companies offer evaluation kits but are not yet in general production.

Efforts are underway to replace alternator incars with a thermoelectric generator mountedon the exhaust stream

to produce electricity rather than using drive train power and an alternator. More drive train power is available to move the vehicle and electricity is still available. Plan is to improve overall fuel economy by 10% and aims to reach production in the 2011-2014

Vehicle waste heat is redirected to a thermoelectric generator

New funding. In the early 1990s DARPA and the Office of Naval Research initiated support for basic thermoelectric materials research: thermoelectric coolers are used for night vision, sensors, guidance systems, etc. and even modest efficiency gains might make TE air conditioning practical in submarines (TE cooling is quiet) and enhance the existing DoD applications.

USS DOLPHIN AGSS 555

–Test for Silent

Running

-A large number of complex materials are now available

At issue are some fundamental scientific challenges, which could be overcome by deeper understanding of heat and charge transport.

Uno si innamora di una idea scientifica come con una donna:all’inizio la conosce poco e non vede i difetti. Quando la conosce bene per vedere i difetti oramai ne e’ innamorato

R. Feynman

HOW FUTURE MAY LOOK LIKE……..

Thermal diodes and transistors

Phys Rev Lett 88 094302 (2002)Phys Rev Lett. 93 184301 (2004)Chaos 15 015120 (2005)Phys Lev Lett 98 104302 (2007)

Thermoelectric

Phys Rev Lett 101 01601 (2008)J Stat Mech L03004 (2009)Phys Rev E 80 010102 (2009)Phys Rev E 80 031136 (2009)