Topic
Thermal radiation
About: Thermal radiation is a research topic. Over the lifetime, 12290 publications have been published within this topic receiving 197186 citations. The topic is also known as: heat radiation.
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TL;DR: In this paper, the authors present the first rigorous quantitative comparison of directional and hemispherical reflectance and directional emittance of rock and soil samples in the laboratory, with thermal gradients induced by heating them from below and allowing them to radiate to a colder background, showing that only an extemeley low density sample composed of fine particles sifted into a "fairy castle" structure displays a thermal gradient steep enough within the infrared skin depth to cause significant (6%) departure from Kirchhoff's law.
Abstract: By the end of this century the Earth Observing System (EOS) will provide worldwide, thermal infrared, multispectral images of the Earth, presenting geologists with a new kind of remote sensing data for interpretation. Thus it has become essential to understand the spectral emittance behavior of terrestrial surface materials. Perhaps the most fundamental question to be answereed is the extent to which such materials follow Kirchhoff's law (epsilon = 1 -R) under laboratory and field conditions, especially when a sample displays a thermal gradient. We present the first rigorous quantitative comparison of directional and hemispherical reflectance and directional emittance of rock and soil samples in the laboratory, with thermal gradients induced by heating them from below and allowing them to radiate to a colder background. The results show that only an extemeley low density sample composed of fine particles sifted into a 'fairy castle' structure displays a thermal gradient steep enough within the infrared skin depth to cause significant (6%) departure from Kirchhoff's law. There is no detectable effect on the more normal terrestrial samples, such as soils and rocks measured in the laboratory, even when semitransparent coatings are involved. Thus both emittance and reflectance measurements can be used to calculate sample emissivity for most terrestrial surface materieals. However, the effect on Kirchhoffian behavior of different field environments, which may induce a steeper thermal gradient in particulate samples, has yet to be determined, and some low-density surface materials like newly fallen snow, frost, and efflorescent salts on playas have yet to be measured in emittance.
248 citations
TL;DR: In this paper, generalized expressions for the emissivity, absorptivity, and other relevant radiation properties of molecular gases are given, and rational correlations for the properties of H2O, CO2, CO, NO, SO2 and CH4 are shown to be readily applicable to combustion gas radiation problems.
246 citations
TL;DR: In this paper, it was shown that neutrinos are emitted preferentially in the direction opposite to the hole's angular momentum, and that in a rotating thermal radiation there exist equilibrium neutrino and antineutrino currents parallel to the angular velocity vector.
Abstract: Two macroscopic effects of parity nonconservation are considered. (i) Particle emission by rotating black holes is shown to be asymmetric. In particular, neutrinos are emitted preferentially in the direction opposite to the hole's angular momentum. (ii) It is shown that in a rotating thermal radiation there exist equilibrium neutrino and antineutrino currents parallel to the angular velocity vector.
243 citations
TL;DR: In this article, the effect of thermal radiation in the linearized Rosseland approximation is shown to be quite trivial, both physically and computationally, and it always reduces to a simple rescaling of the Prandtl number by a factor involving the radiation parameter.
238 citations
TL;DR: A refractory W-HfO2 metamaterial is demonstrated, which controls thermal emission through an engineered dielectric response function, marking a paradigm shift in thermal engineering approaches.
Abstract: Control of thermal radiation at high temperatures is vital for waste heat recovery and for high-efficiency thermophotovoltaic (TPV) conversion. Previously, structural resonances utilizing gratings, thin film resonances, metasurfaces and photonic crystals were used to spectrally control thermal emission, often requiring lithographic structuring of the surface and causing significant angle dependence. In contrast, here, we demonstrate a refractory W-HfO2 metamaterial, which controls thermal emission through an engineered dielectric response function. The epsilon-near-zero frequency of a metamaterial and the connected optical topological transition (OTT) are adjusted to selectively enhance and suppress the thermal emission in the near-infrared spectrum, crucial for improved TPV efficiency. The near-omnidirectional and spectrally selective emitter is obtained as the emission changes due to material properties and not due to resonances or interference effects, marking a paradigm shift in thermal engineering approaches. We experimentally demonstrate the OTT in a thermally stable metamaterial at high temperatures of 1,000 °C. The ability to control thermal radiation at high temperatures is of interest for thermal photovoltaics. Here, Dyachenko et al. engineer the epsilon-near-zero frequency of a metamaterial and connected optical topological transition to selectively enhance and suppress the thermal emission in the near-infrared spectrum.
236 citations