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Near-field radiative heat transfer : application to energy conversion

Near-field radiative heat transfer : application to energy conversion. Jean-Jacques Greffet Ecole Centrale Paris, CNRS. Rémi Carminati, O. Chapuis, K. Joulain, F. Marquier, J.P. Mulet, M. Laroche, S. Volz C. Henkel ( Potsdam) A. Shchegrov ( Rochester)

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Near-field radiative heat transfer : application to energy conversion

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  1. Near-field radiative heat transfer :application to energy conversion Jean-Jacques Greffet Ecole Centrale Paris, CNRS.

  2. Rémi Carminati, O. Chapuis, K. Joulain, F. Marquier, J.P. Mulet, M. Laroche, S. Volz C. Henkel ( Potsdam) A. Shchegrov ( Rochester) Y. Chen, S. Collin, F.Pardo, J.L. Pelouard ( LPN, Marcoussis) Y. de Wilde, F. Formanek, P.A. Lemoine ( ESPCI) Collaborators

  3. Density of energy above a SiC surface at temperature T z Temperature T

  4. Density of energy near a SiC-vacuum interface z T=300 K PRL, 85 p 1548 (2000)

  5. Density of energy near a SiC-vacuum interface z T=300 K PRL, 85 p 1548 (2000)

  6. Density of energy near a SiC-vacuum interface z T=300 K PRL, 85 p 1548 (2000)

  7. Density of energy near a Glass-vacuum interface z T=300 K

  8. What is the physical mechanism responsible for this huge enhancement ? The density of energy is the product of - the density of states, - the energy hn - the Bose Einstein distribution. The density of states can diverge due to the presence of surface waves : Surface phonon-polaritons.

  9. + - + - + - + - + - +

  10. + - + - + - + - - - + - +

  11. Dispersion relation of a surface phonon-polariton It is seen that the number of modes diverges for a particular frequency. This happens only close to the surface. PRB, 55 p 10105 (1997)

  12. Derivation of the thermal emission of a hot body i) A volume element below the interface contains currents due to the random thermal motion of charges. ii) Each volume element is equivalent to a dipolar antenna that emits radiation. iii) The mean field is null. PRL, 82 p 1660 (1999)

  13. iv) Derivation of the intensity v) The only quantity needed is the correlation function of the random current. This is given by the fluctuation-dissipation theorem. PRL, 82 p 1660 (1999)

  14. Advantages of the electromagnetic approach • It is valid in the near field • It yields the value of the emissivity • It yields physical insight in Kirchhoff law.

  15. Direct proof of the coherence of thermal radiation in the near field. Application to the measurement of the EM LDOS

  16. Direct experimental evidence of the spatial coherence of thermal radiation in near field de Wilde et al. to be published in Nature

  17. Direct experimental evidence of the spatial coherence of thermal radiation in near field de Wilde et al. to be published in Nature

  18. Fabrication of a coherent source of infrared radiation : Infrared antenna

  19. M P z r T=300 K The thermally emitted fields may be spatially coherent along the interface ! PRL 82, 1660 (1999)

  20. Fabricating an infrared antenna with a microstructured semiconductor. Thermal currents radiates surface waves A grating ruled on the surface scatters the surface wave. The scattered wavevector is related to the surface wave wavevector by the relationship : q

  21. Image of the SiC grating taken with an atomic force microscope. Nature 416, p 61 (2002)

  22. Emission pattern of a SiC grating Green line : theory (300K) Red line : measurement (800K). Nature 416, p 61 (2002) The emission pattern looks like an antenna emission pattern. The angular width is a signature of the spatial coherence.

  23. Comparison between theory and measurements Nature 416, p 61 (2002)

  24. Thermal emission by a tungsten grating Angular width : 14 mrad Opt.Lett. 30 p 2623 (2005)

  25. Emission mediated by surface waves Excitation of a surface wave. 2. Scattering by a grating.

  26. Coherent thermal emission T Source : current thermal fluctuations Emission mediated by surface waves Greffet et al., Nature (London) 416, 61 (2002), Marquier et al. PRB 69, 155412 (2004)

  27. The interface as an antenna (1) • What is an antenna ? i) Increases the emitted power. ii) Modifies the emission pattern. • How does it work ? • Antenna = Intermediate resonator between the source and vacuum : • i) More energy is extracted from the source because the LDOS is enhanced (Purcell effect) • ii) The resonator is a secondary source.

  28. Resonator Source : the string The interface as an antenna (2) Example of antenna: a guitar Optical analog : microcavity

  29. The interface as an antenna (3) Resonator : the interface + the grating T Source : current fluctuations The output is increased because the LDOS is increased (Purcell effect) ii) The angular pattern of the antenna depends on the decay length of the SPP.

  30. Electromagnetic heat transfer in the near field

  31. Application to radiative heat transfer between two half-spaces Temperature T1 d F Temperature T2>T1. Poynting vector yields the radiative enregy flux.

  32. Radiative heat transfer coefficient, T=300 K. d

  33. Monochromatic radiative heat transfer coefficient, d=10 nm, T=300K. d Microscale Thermophysical Engineering 6, p 209 (2002)

  34. Experimental data Au GaN Kittel et al. , PRL 95 p 224301 (2005)

  35. Implications of near-field heat transfer for thermophotovoltaics

  36. thermal source T= 2000 K d << rad TPV cell T= 300 K TPV cell PV cell T= 300 K T= 300 K Near-field thermophotovoltaics Photovoltaics Thermophotovoltaics T= 6000K thermal source T= 2000 K

  37. Why near field ? potential improvement on the output electric power and efficiency of near-field thermophotovoltaic devices : necessity of a quantitative model thermal source T= 2000 K d << rad TPV cell T= 300 K enhanced radiative power transfer 400 PR ( W.m-2 ) d (m)

  38. enhanced radiative power (Mulet 2002, Whale 2002, Chen 2003) hot source T= 2000 K d <<rad TPV cell T= 300 K Near-field I-V characteristic of a TPV cell z modification of the electron-hole pairs lifetime (Baldasaro 2001)

  39. PR(W. m-2. Hz-1)  (rad.s-1) PR(W. m-2. Hz-1) evanescent waves contribution in the near field enhancement by a factor 3  (rad.s-1) Near-field radiative power transfer 1.10-10 W d = 10 m T= 2000 K (far field) d 3.5.10-10 GaSb cell d = 30 nm T= 300 K (near field)

  40. Drude Metal T= 2000 K PR(W. m-2. Hz-1) d  (rad.s-1) GaSb cell T= 300 K PR(W. m-2. Hz-1)  (rad.s-1) Near-field effects on the radiative power transfer 9.10-12 d = 10 m (far field) 6.10-10 d = 30 nm (near field) evanescent waves contribution in the near field enhancement by two orders of magnitude monochromaticity degraded by the presence of the TPV converter

  41. Enhanced radiative transfer and photogeneration current in the near field tungsten source quasi-monochromatic source 50 PR ( W.m-2 ) 400 PR ( W.m-2 ) d (m) d (m) 40 1000 Iph ( A.m-2 ) Iph ( A.m-2 ) d (m) d (m)

  42. hot source d << rad vacuum z GaSb Near-field electron-hole pairs lifetime for both sources : near-field effect on the radiative recombination lifetime of electron-hole pairs negligible

  43. Near-field output electric power tungsten source quasi-monochromatic source near field :15.105 W/m2 near field : 2.5.106 W/m2 Pel (W. m-2) 50 3000 Pel (W. m-2) far field :3.104 W/m2 BB 2000 K far field : 1.4.103 W/m2 BB 2000 K d (m) d (m) output electric power enhanced by at least one order of magnitude

  44.  (%) d (m)  (%) d (m) Near-field TPV converter efficiency quasi-monochromatic source tungsten source near field : 35% near field : 27% far field : 21 % far field : 8 % BB 2000 K BB 2000 K significant increase of the efficiency

  45. Summary ?

  46. Heat transfer between two nanoparticles

  47. Heat transfer between two nanoparticles PRL 94, 85901, (2005)

  48. PRL 94, 85901, 2005

  49. Radiative heat transfer between a small sphere and an interface d Appl.Phys.Lett, 78, 2931 (2001)

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