Non-classical Heat Radiation & Transfer
Radiation Pressure from a hot-plate can in principle counteract Casimir attraction
cf.
Around room temperature, this is for distances exceeding 7 microns; somewhat large for practical applications,
while at short separations "near-field effects" due to evanescent waves lead to non-classical behavior.
Breaking the law, at the nanoscale (MIT news, July 29, 2009)
"Surface Phonon Polaritons Mediated Energy Transfer between Nanoscale Gaps,"
S. Shen, A. Narayanaswamy, & G. Chen, Nano Lett. 9, 2909 (2009)
Heat transfer between plates diverges at short distances due to evanescent waves (tunneling).
A generalized scattering approach enables computation of Casimir forces, as well as radiation and heat transfer,
in non-equilibrium steady states.
"Nonequilibrium Electromagnetic Fluctuations: Heat Transfer and Interactions,"
M. Krüger, T. Emig, and M. Kardar, Phys. Rev. Lett. 106, 210404 (2011)
Rytov (1959): "Fluctuational QED"
Fluctuating currents in each object are related to its temperature by a fluctuation-dissipation condition:
The EM field due to thermal fluctuations of one object is related to overall Green's function by:
The overall fluctuations with many objects at different temperatures is then given by:
From EM correlations follow the stress tensor and the Poynting vector, hence forces and radiation.
Heat Transfer from a plate to a sphere (and other objects at proximity):
Due to its "divergence" heat transfer is dominated by points of close proximity.
A "Proximity Transfer Approximation (PTA)" with "gradient correction" can by used to compute results for arbitrary smooth shapes at close proximity.
Emission from a single object (Sphere or Cylinder):
Emission is proportional to volume for small objects, crossing over to surface proportionality.
Emission from a cylinder is polarized (also switching as a function of size)
"Thermalization of Heat radiation of an Individual Object Thinner than the Thermal Wavelength,"
C. Wuttke and A. Rauschenbeutel, Phys. Rev. Lett. 111, 024301 (2013)