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Efficiency of thermal radiation energy-conversion nanodevices
Miguel Rubi
I. LatellaA. PerezL. Lapas
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Enhancement of the heat flux in the near-field
Heat Transfer coefficient
Hu et al., Appl. Phys. Lett. 92, 133106 (2008)
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Thermal conductance
Domingues et al., Phys. Rev. Lett. 94, 085901 (2005)
Molecular dynamics
Th
erm
al c
on
du
ctan
ce
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Fluctuation-dissipation regime
FDT
Fluctuating electrodynamics
Domingues et al., PRL, 94, 085901 (2005)
Valid when thermalization is very fast
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Beyond the dipolar approximation…
A.Pérez, J.M.Rubi., L. Lapas, Phys. Rev. B 77, 155417 (2008)
Dipolar approximation: d>8RDomingues et al.,PRL, 94, 085901 (2005)
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Equilibrium photon gas
4eqJ T
Energy conservation# microstates
Planck distribution
Stefan-Boltzmann
1
exp 1N
kT
TdS=dE
Planck’s theory is not valid when length scales are comparable to the wave length of thermal radiation
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Nonequilibrium photon gasStatistics:
Thermodynamics:
D. Reguera, J.M. Rubi and J.M. Vilar, J. Phys. Chem. B (2005)
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Entropy production
Onsager coefficient
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Non-equilibrium Stefan-Boltzmann law
( ) ( ) ( ) ( , ) ( , )st L R R LJ D D n T n T
1
( , )exp / 1
n TkT
3 4 43 3
( ) ( )4st p st R LJ d d J T Tc
Shorter distances, no longer validNear-field thermodynamics
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ELECTROMAGNETIC WAVES CONFINED IN A VERY NARROW GAP
Spectrum of electromagnetic energy for different detection distances above surface of silicon carbide normalized by its maximum value in far field at T= 300 K. (J.-J. Greffet and C. Henkel, 2007)
11
When the distance diminishes, thermal radiation becomes a highly directional beam of coherent radiation.
The narrow gap acts as a resonant cavity
Electromagnetic energy density above a plane interface separating glass (amorphous, optical phonons poorly defined) at T = 300 K from vacuum at T = 0 K
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Photon Kinetics
2 1*
*
( )
( ) ( )
J n n
t n n d
) ;
)
;
T
T
R
i d black body
ii d
x p h
h Kcp E h h
d d
pp xxpx
xp
D D nJ D
D x
A. Perez, L. Lapas, J.M. Rubi, PRL, 103, 048301 (2009)
Heat flux results from the contribution ofDifferent modes
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Input of the theory
Elastic:
Inelastic:
Lognormal DOS
-Statistical model which can describe collective motions.-Stems from the existence of a hierarchy of relaxations mechanisms in the material-The energy consists of a large number of contributions; central limit theorem
Y. V. Denisov, A.P. Rylev, JEPT Lett. 52, 411 (1990)0: ,Fitting parameters
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14
Yu. V. Denisov and A.P. Rylev, JETP Lett. 52 (1990), 411.
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Heat transfer coefficient
15
A. Perez, L. Lapas, J.M. Rubi, PRL, 103, 048301 (2009)
FF
NF
30
0
H T
H T
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A. Perez-Madrid, L. Lapas, J.M. Rubi, Plos One, 8, e58770 (2013)
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The system
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Efficiency
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Near-field
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Black body
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Conclusions
• Near-field thermal radiation dramatically increases the amount of energy exchanged between bodies separated by a nanogap as compared to the black-body limit.
• We have evaluated the heat transfer coefficient and the thermal conductance in a wide range of length scales, giving a thermokinetic description of several experiments involving heat radiation through a very narrow gap.
• The theory presented may also be used in the study of other heat exchange processes such as those occurring in phonon systems and in the analysis of thermal contributions to Casimir forces.
• Near-field energy converters are more efficient than devices working in the black-body limit.