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# Near-Field Radiative Heat Transfer between Macroscopic Planar Surfaces

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Department of Physics, University of Florida, Gainesville, 32611-8440, USA.
(Impact Factor: 7.73). 03/2011; 107(1). DOI: 10.1103/PhysRevLett.107.014301
Source: arXiv

ABSTRACT Near-field radiative heat transfer allows heat to propagate across a small
vacuum gap in quantities that are several orders of magnitude greater then the
heat transfer by far-field, blackbody radiation. Although heat transfer via
near-field effects has been discussed for many years, experimental verification
of this theory has been very limited. We have measured the heat transfer
between two macroscopic sapphire plates, finding an increase in agreement with
expectations from theory. These experiments, conducted near 300 K, have
measured the heat transfer as a function of separation over mm to $\mu$m and as
a function of temperature differences between 2.5 and 30 K. The experiments
demonstrate that evanescence can be put to work to transfer heat from an object
without actually touching it.

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ABSTRACT: We derive shape-independent limits to the spectral radiative heat-transfer rate between two closely spaced bodies, generalizing the concept of a black body to the case of near-field energy transfer. By conservation of energy, we show that each body of susceptibility $\chi$ can emit and absorb radiation at enhanced rates bounded by $|\chi|^2 / \operatorname{Im} \chi$, optimally mediated by near-field photon transfer proportional to $1/d^2$ across a separation distance $d$. Dipole--dipole and dipole--plate structures approach restricted versions of the limit, but common large-area structures do not exhibit the material enhancement factor and thus fall short of the general limit. By contrast, we find that particle arrays interacting in an idealized Born approximation exhibit both enhancement factors, suggesting the possibility of orders-of-magnitude improvement beyond previous designs and the potential for radiative heat transfer to be comparable to conductive heat transfer through air at room temperature, and significantly greater at higher temperatures.
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