Corps noir | EPFL Graph Search

En physique, un corps noir est un objet idéal qui absorbe parfaitement toute l'énergie électromagnétique (toute la lumière quelle que soit sa longueur d'onde) qu'il reçoit. Cette absorption se traduit par une agitation thermique qui provoque l'émission d'un rayonnement thermique, dit rayonnement du corps noir. La loi de Planck décrit le spectre de ce rayonnement, qui dépend uniquement de la température de l'objet. La loi du déplacement de Wien détermine la longueur d'onde de la luminance spectrale maximale, et la loi de Stefan-Boltzmann donne la densité de flux d'énergie émise, qui ne dépend elle aussi que de la température de l'objet. Le nom corps noir a été introduit par le physicien Gustav Kirchhoff en 1859. Le modèle du corps noir permit à Max Planck de découvrir la quantification des interactions électromagnétiques, qui fut un des fondements de la physique quantique. Le modèle du corps noir Le corps noir est un objet idéal qui absorberait parfaitement toute l'énerg

Energy-Efficient Sol-Gel Process for Production of Nanocomposite Absorber Coatings for Tubular Solar Thermal Collectors

Yannik Antonetti, Marina Garcia Gonzalez, Thomas Gascou, Martin Joly, Martin Python, Andreas Schueler

The energy efficiency of production processes for components of solar energy systems is an important issue. Other factors which are important for the production of products such as black selective solar coatings include production speed, cycle time and homogeneity of the coating, as well as the minimization of the quantity of the needed chemical precursors. In this paper a new energy efficient production process is presented for production of optically selective coatings for solar thermal absorbers. The latter should ideally behave as a black body, absorbing a maximum of the incoming solar radiation, while minimizing energy losses by infrared radiation, acting as an infrared mirror. The used method to produce such coatings is sol-gel dip-coating. The optical and morphological properties of the Cu-Co-Mn-Si-O based triple layer have been characterized by spectrophotometry, electron microscopy and time of flight secondary electron microscopy. After optimization of the multilayer design, a solar absorptance of 0.95 and a thermal emissivity of 0.12 at 100°C have been achieved. The intermediate Cu-Co-Mn-Si-O layer was analyzed by high resolution transmission electron microscopy. The likewise obtained images show an agglomeration of crystalline grains with 10-20nm in diameter. Therefore, we can consider that the Cu-Co-Mn-Si-O phase is nanocrystalline. In order to roughly estimate the corrosion resistance of the coating in an acidic environment, a simple corrosion test in harsh conditions was designed. With respect to a commercially available durable black chrome coating, this test of corrosion resistance confirmed the durability of the novel sol-gel coating in an acidic environment. Moreover, the excellent stability at elevated temperatures in ambient air makes the coating an interesting candidate for solar applications involving concentrated solar radiation, such as the generation of solar electricity (concentrated solar power), industrial process heating and solar cooling. For that reason, prototype coatings consisting of stacks of three individual layers were deposited on 2 meter long stainless steel tubes.

EPFL Solar Energy and Building Physics Laboratory (LESO-PB)2013

Planck 2013 results. XI. All-sky model of thermal dust emission

Fabio Finelli, Julien Lesgourgues

This paper presents an all-sky model of dust emission from the Planck 353, 545, and 857 GHz, and IRAS 100 mu m data. Using a modified blackbody fit to the data we present all-sky maps of the dust optical depth, temperature, and spectral index over the 353-3000 GHz range. This model is a good representation of the IRAS and Planck data at 5 0 between 353 and 3000 GHz (850 and 100 mu m). It shows variations of the order of 30% compared with the widely-used model of Finkbeiner, Davis, and Schlegel. The Planck data allow us to estimate the dust temperature uniformly over the whole sky, down to an angular resolution of 5 0, providing an improved estimate of the dust optical depth compared to previous all-sky dust model, especially in high-contrast molecular regions where the dust temperature varies strongly at small scales in response to dust evolution, extinction, and/or local production of heating photons. An increase of the dust opacity at 353 GHz, tau(353)/N-H, from the diffuse to the denser interstellar medium (ISM) is reported. It is associated with a decrease in the observed dust temperature, T-obs, that could be due at least in part to the increased dust opacity. We also report an excess of dust emission at HI column densities lower than 10(20) cm(-2) that could be the signature of dust in the warm ionized medium. In the diffuse ISM at high Galactic latitude, we report an anticorrelation between tau(353)/N-H and T-obs while the dust specific luminosity, i.e., the total dust emission integrated over frequency (the radiance) per hydrogen atom, stays about constant, confirming one of the Planck Early Results obtained on selected fields. This e ff ect is compatible with the view that, in the diffuse ISM, Tobs responds to spatial variations of the dust opacity, due to variations of dust properties, in addition to (small) variations of the radiation field strength. The implication is that in the di ff use high-latitude ISM tau(353) is not as reliable a tracer of dust column density as we conclude it is in molecular clouds where the correlation of tau(353) with dust extinction estimated using colour excess measurements on stars is strong. To estimate Galactic E(B-V) in extragalactic fields at high latitude we develop a new method based on the thermal dust radiance, instead of the dust optical depth, calibrated to E(B-V) using reddening measurements of quasars deduced from Sloan Digital Sky Survey data.

Edp Sciences S A2014

Rapid-Response Low Infrared Emission Broadband Ultrathin Plasmonic Light Absorber

Dimos Poulikakos, Giulia Tagliabue

Plasmonic nanostructures can significantly advance broadband visible-light absorption, with absorber thicknesses in the sub-wavelength regime, much thinner than conventional broadband coatings. Such absorbers have inherently very small heat capacity, hence a very rapid response time, and high light power-to-temperature sensitivity. Additionally, their surface emissivity can be spectrally tuned to suppress infrared thermal radiation. These capabilities make plasmonic absorbers promising candidates for fast light-to-heat applications, such as radiation sensors. Here we investigate the light-to-heat conversion properties of a metal-insulator-metal broadband plasmonic absorber, fabricated as a free-standing membrane. Using a fast IR camera, we show that the transient response of the absorber has a characteristic time below 13 ms, nearly one order of magnitude lower than a similar membrane coated with a commercial black spray. Concurrently, despite the small thickness, due to the large absorption capability, the achieved absorbed light power-to-temperature sensitivity is maintained at the level of a standard black spray. Finally, we show that while black spray has emissivity similar to a black body, the plasmonic absorber features a very low infra-red emissivity of almost 0.16, demonstrating its capability as selective coating for applications with operating temperatures up to 400°C, above which the nano-structure starts to deform.