Going hundreds to millions of times beyond blockbody limit for radiative heat transfer

Here are three papers about going hundreds to millions of times beyond radiative heat transfer beyond the blackbody limit.

Nanoletters – Giant Enhancement in Radiative Heat Transfer in Sub-30 nm Gaps of Plane Parallel Surfaces

Radiative heat transfer rates that exceed the blackbody limit by several orders of magnitude are expected when the gap size between plane parallel surfaces is reduced to the nanoscale. To date, experiments have only realized enhancements of ∼100 fold as the smallest gap sizes in radiative heat transfer studies have been limited to ∼50 nm by device curvature and particle contamination. Here, we report a 1,200-fold enhancement with respect to the far-field value in the radiative heat flux between parallel planar silica surfaces separated by gaps as small as ∼25 nm. Achieving such small gap sizes and the resultant dramatic enhancement in near-field energy flux is critical to achieve a number of novel near-field based nanoscale energy conversion systems that have been theoretically predicted but remain experimentally unverified.

Hundred-fold enhancement in far-field radiative heat transfer over the blackbody limit

Nature – Hundred-fold enhancement in far-field radiative heat transfer over the blackbody limit

Radiative heat transfer (RHT) has a central role in entropy generation and energy transfer at length scales ranging from nanometers to light years. The blackbody limit, as established in Max Planck’s theory of RHT, provides a convenient metric for quantifying rates of RHT because it represents the maximum possible rate of RHT between macroscopic objects in the far field—that is, at separations greater than Wien’s wavelength. Recent experimental work has verified the feasibility of overcoming the blackbody limit in the near field but heat-transfer rates exceeding the blackbody limit have not previously been demonstrated in the far field. Here we use custom-fabricated calorimetric nanostructures with embedded thermometers to show that RHT between planar membranes with sub-wavelength dimensions can exceed the blackbody limit in the far field by more than two orders of magnitude. The heat-transfer rates that we observe are in good agreement with calculations based on fluctuational electrodynamics. These findings may be directly relevant to various fields, such as energy conversion, atmospheric sciences and astrophysics, in which RHT is important.

Super-Planckian far-field radiative heat transfer that would more than 7 orders of magnitude larger than the theoretical limit set by Planck’s law for blackbodies

Arxiv – Exploring the limits of super-Planckian far-field radiative heat transfer using 2D materials

Very recently it has been predicted that the far-field radiative heat transfer between two macroscopic systems can largely overcome the limit set by Planck’s law if one of their dimensions becomes much smaller than the thermal wavelength (λTh ≈ 10 µm at room temperature). To explore the ultimate limit of the far-field violation of Planck’s law, here we present a theoretical study of the radiative heat transfer between twodimensional (2D) materials. We show that the far-field thermal radiation exchanged by two coplanar systems with a one-atom-thick geometrical cross section can be more than 7 orders of magnitude larger than the theoretical limit set by Planck’s law for blackbodies and can be comparable to the heat transfer of two parallel sheets at the same distance. In particular, we illustrate this phenomenon with different materials such as graphene, where the radiation can also be tuned by a external gate, and single layer black phosphorus. In both cases the far-field radiative heat transfer is dominated by TE-polarized guiding modes and surface plasmons play no role. Our predictions provide a new insight into the thermal radiation exchange mechanisms between 2D materials.

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