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Energy and the First Law of Thermodynamics
Published in Kavati Venkateswarlu, Engineering Thermodynamics, 2020
where TS is the absolute temperature (K) of the surface and σ is the Stefan–Boltzmann constant (σ = 5.67 × 10−8 W/m2 K4). A black body is an idealized body that emits maximum radiation. The radiation emitted by all real surfaces is less than that emitted by a black body at the same temperature, given by E=εσTs4
Cryogenic Cooling Strategies
Published in Raja Sekhar Dondapati, High-Temperature Superconducting Devices for Energy Applications, 2020
Sudheer Thadela, Raja Sekhar Dondapati
Thermal radiation problems: According to Wien’s law, the wavelength at which peak radiant intensity occurs for blackbody radiation is inversely proportional to the absolute temperature. For example, at 1 K, the peak occurs at a wavelength of ~2.9 mm. Most metallic shields which are employed for reducing radiation heat transfer into cryogenic systems will have a thickness which is comparable to or less than this value. Hence, the treatment of radiation problems at cryogenic temperatures can be significantly different compared to materials at room temperature, where the wavelength peak occurs at ~0.009 mm.
Example labs
Published in Martin Novák, Introduction to Sensors for Electrical and Mechanical Engineers, 2020
The radiation of a black body is described by the Planck’s law. It relates the spectral radiance of a black body (the quantity of radiation) with its temperature and wavelength of the radiation. A blackbody emits total radiant power WB into a surrounding hemisphere given by WB=σ⋅T4 where σ is Stefan-Boltzman constant, and T is temperature in Kelvin.
Measurements of Total Hemispherical Emissivity of A508/A533B Alloy Steel
Published in Nuclear Technology, 2019
Faten N. Al Zubaidi, Kyle L. Walton, Robert V. Tompson, Tushar K. Ghosh, Sudarshan K. Loyalka
Emissivity is fundamentally a surface property of a material and is defined as the ratio of the emission from the material surface to the emission from a black body (perfect emitter) at the same temperature and under the same conditions. Emissivity can be strongly affected by a number of surface conditions such as oxidation, coating, roughness, chemical composition, and physical structure.10–16 Optical measurements of emissivity are usually over a band of narrow wavelengths normal to the surface, thus emissivity data are described as spectral normal emissivity. The total hemispherical emissivity is an integrated quantity over the spectral and angular emissivity (that is, over all wavelengths and 2π solid angle). Calorimetric methods directly determine total hemispherical emissivity by measuring the heat transferred between the heated specimen and its enclosure, which is evacuated. The distinction is important when doing radiant heat transfer calculations. For example, the accident-progression modeling computer program MELCOR calculates radiant heat transfer within the reactor core and lower plenum by assuming surfaces are gray and diffuse emitters.17 A gray surface or body is one whose emissivity is independent of the wavelength of radiation.18 In such calculations, the total hemispherical emissivity would be more useful and pertinent as it represents most of the radiant energy transferred by the surface. The surfaces, thus emissivity, of the reactor vessel and structural materials are expected to change during the lifetime of the reactor or during an accident, notably oxidation. Knowing the variation of emissivity from surface changes as a function of temperature is important for accurate calculations in MELCOR.
The Effect of Long-Term Oxidation on the Total Hemispherical Emissivity of Type 316L Stainless Steel
Published in Nuclear Technology, 2018
Faten N. Al Zubaidi, Kyle L. Walton, Robert V. Tompson, Tushar K. Ghosh, Sudarshan K. Loyalka
Emissivity is fundamentally a surface property of a material and is defined as the ratio of radiated energy emitted from a material’s surface to the radiated energy that would be emitted from a blackbody at the same temperature. Emissivity can be strongly affected by a number of surface conditions such as oxidation, coating, roughness, etc.5–10 There have been a number of studies demonstrating the effect of oxidation on the total hemispherical emissivity of various materials.11–14
An experimental study on the evaluation of temperature uniformity on the surface of a blackbody using infrared cameras
Published in Quantitative InfraRed Thermography Journal, 2022
S.T. Yoon, J.C. Park, Y.J. Cho
Radiation here refers to thermal energy emitted from an object in the form of electromagnetic waves. A blackbody refers to an ideal diffuse emitter that absorbs all energy, irrespective of its wavelength and direction, and re-emits the maximum energy at a given temperature and in a predictable wavelength profile. Blackbody radiation can thus be used as a reference model to compare radiant energy emitted from actual surfaces [1–3].