Seminario del Prof. Giulio Casati 25 marzo 2010 in occasione del primo MicroEnergy Day

1. CENTER FOR NONLINEAR AND COMPLEX SYSTEMS Como - Italy The purpose of this talk is to understand the properties of the heat Transport from the microscopic dynamical eqs. of motion In particular if we can control the hear current as we do for example With the electric current

4. Providing a sustainable supply of energy to the world’s population will become a major societal problem for the 21 st 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

5. ‘ It seems there is no problem in modern physics for which there are one record as many false starts and as many theories which overlook some essential features as in the problem of the thermal conductivity of non conducting crystals’ R. E. PEIERLS

6. J. B. FOURIER 1808 - Attempt to explain the thermal gradient inside the earth

7. QUESTION: Can one derive the Fourier law of heat conduction from dynamical equations of motion without any statistical assumptions? Normal transport

8. REMARK: Randonmnes is an essential ingredient of thermal conductivity deterministically random systems are tacitly required by the transport theory

9. THE DING-A -LING MODEL

10. THE DING-A -LING MODEL

13. J. B. FOURIER 1808 - Attempt to explain the thermal gradient inside the earth

15. Nature, 7 june 1984

16. FOURIER LAW IN QUANTUM MECHANICS?

17. FOURIER LAW IN QUANTUM MECHANICS? Deterministic chaos appear to be an important ingredient for Fourier law. No exponential instability in Quantum Mechanics

18. FOURIER LAW IN QUANTUM MECHANICS? Deterministic chaos appear to be an important ingredient for Fourier law. No exponential instability in Quantum Mechanics Terra Incognita

21. SIGNATURES OF QUANTUM CHAOS The distribution of energy levels spacings obeys the Wigner-Dyson surmise RANDOM MATRIX THEORY

22. Lettere al Nuovo Cimento 28 (1980) 279

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

28. Plane waves solutions Dispersion relations Phonon band

32. INTERNAL TEMPERATURE PROFILE

33. In nonlinear systems the position of the band depends on the temperature

34. p.r.l. 88, (2002)

36. For uniform mass distribution, thermal conduction is symmetric

38. All measurements showed that a higher thermal conductance was observed when heat flowed from the high-mass region to the low -mass region

39. NEGATIVE DIFFERENTIAL THERMAL CONDUCTIVITY

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

44. 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.

45. 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 home refrigerators and power generators

46. Here comes another talk on fundamental limits

47. Thermoelectricity concerns the conversion of temperatures differencies into electrical potential or viceversa It can be used to perform useful electrical work or to pump heat from cold to hot place, thus performing refrigeration

48. The field of thermoelectric advanced rapidly in the 1950s when the basic science of thermoelectric materials became well established, the thermoelectric material Bi 2 Te 3 was developed for commercialization, thus launching the thermoelectric industry Thermoelectric (Peltier) refrigerators have poor efficiency compared to compressor-based refrigerators.

49. 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 missions laboratory equipment medical applications where cost and energy efficiency were not as important as energy availability, reliability, predictability, and the quiet operation of equipment.

50. devices used for cooling, and for power generation Voyager mission to Jupiter and Saturn, here at its launch in 1977.

51. Thermoelectric devices provide on board power to operate 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.

53. 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 thermocouples have accumulated more than a trillion device-hours without a single failure.

54. - Key step 1990 : first significant consumer product, picnic basket cooler - Thermoelectric industry stable and growing

55. Thermoelectric coolers/heaters by “Amerigon“(USA)

56. -2 milion climate control seats in 2006 Estimate 2% reduction in fuel consumption -World market in 2010 up to 1 billion US$

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

58. The ZT figure of merit The suitability of a thermoelectric material for energy conversion or electronic refrigeration is evaluated by

59. The conversion efficiency is given by

61. In five decades the ZT of semiconductors has increased only marginally, from about 0.6 to 1 A. Majumdar Science 303, 777(2004)

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

63. Metals are poor thermoelectric materials because of low Seebeck coefficient and large electronic contribution to thermal conductivity. A ZT value > 3 would make solid –state home refrigerators economically competitive with compressor-based refrigerators

64. Metals are poor thermoelectric materials because of low Seebeck coefficient and large electronic contribution 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

66. ZT =1.5

67. Mass ratio

68. R radius of scatterers

69. Heterogeneous channel

70. If If and

73. When the number d int of internal degrees of freedoms of moving particles become large

75. G.C , C.Monasterio, T. Prosen, Phys. Rev. Lett. 101 , 016601(2008) ZT increases with geometrical and internal degrees of freedom D of gas particles.

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

78. 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 well superlattice’, has been important for inspiring nano-scale engineering to improve ZT.

79. -Environmental concern about chlorofluorocarbons used in most compression-based refrigeration technologies. -Home heating, automotive exhaust, etc. generate an enormous amount of unused waste heat - Generation of electric power from waste heat using thermoelectrics is becoming more and more attractive (e.g. automobile exhaust and engine heat)

80. 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.

81. Efforts are underway to replace alternator in cars with a thermoelectric generator mounted on the exhaust stream

82. 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

83. 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

85. 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

86. HOW FUTURE MAY LOOK LIKE……..

87. 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)