Radiative power

Emissive power is the total radiative power leaving the surface of the fire per unit area and per unit time. Emissive power can be calculated by use of Stefan s law, which gives the radiation of a black body in relation to its temperature. Because the fire is not a perfect black body, the emissive power is a fraction (e) of the black body radiation ... 

The radiative power per unit area intercepted by some plane in the environment can now be computed from ... 

Emissive power The total radiative power discharged from the surface of a fire per unit area (also referred to as surface-emissive power). 

For two plane parallel surfaces, both of area A and of emissivities s2 at respective temperatures 7j and T2, the radiative power transfer is ... 

The low-temperature working space was surrounded by a copper thermal shield at the temperature of the mixing chamber, hence, the radiative power was always negligible. For electrical connections, RF filters both at room temperature and at 4K were used the total spurious power on the sample was estimated to be below 10-11 W. 

A similar analysis may be made for the 1D case.126 The interaction energies / (co) then show an enhancement of the order of k/a 103 relative to the parameters of the isolated point dipole, which is easily overwhelmed by nonradiative processes. Using the simple golden rule image, we may say that the transition dipole shows a huge increase from 0D to 3D systems, while the effective photon continuum density varies in an opposite (in fact complementary) way as follows, with radiative-power optimization for 2D systems ... 

Line sources are essential in AAS to obtain adequate sensitivity with a monochromator of only moderate resolution (see Chapter 1, section 7), to make sure that 7t is substantially less than /0. In theory, at least, modulated continuum sources may be used in AFS, because the readily isolated fluorescence emission following radiative excitation is characteristic of the element under investigation. For this reason, AFS is sometimes termed a self-monochromating technique . However the radiative power from a continuum source which falls within the very narrow line width of a typical absorption profile is very small, even if the continuum source is very intense. Therefore detection AFS limits obtained with a source such as a 500 W xenon arc lamp are very poor.34,35 Generally line sources, especially EDLs, are used as excitation sources (see section 3). 

Fig. 18.1. Series 4 concerns the ground and metastable populations of ions in a plasma and their preparation and calculation for dynamical plasma models. It operates with GCR recombination and ionization coefficients, associated power loss coefficients and metastable fractions. The scope of series 4 is quite large extending into short wavelength filters modifying observed radiative power, astrophysical contribution function generation and parametrization of ionization and recombination...

When comparing different solar collectors it is important to take into account the different quantities of radiation collected in each case. For a given receiver, the radiative power collected increases with aperture size (i.e., with concentration). However, this is not a linear effect and, for instance, a CPC with a two suns concentration ratio provides twice the aperture area of a nonconcentrating CPC. Nevertheless the power received by the tubular absorber is not doubled, because the former CPC misses around half of the diffuse radiation. Other important consideration is the fact that concentrating reactors are faster simply because they collect more radiation, which is associated with larger collector area. 

The total rate of heat generation due to the ga -phase exothermal reaction is equal to or greater than the rate of radiative power absorption by the solid phase ... 

Although various restrictions have been placed on carbon particulate emissions from different types of power plants, these particles can play a beneficial, as well as a detrimental, role in the overall plant process. The detrimental effects are well known. The presence of particulates in gas turbines can severely affect the lifetime of the blades soot particulates in diesel engines absorb carcinogenic materials, thereby posing a health hazard. It has even been postulated that, after a nuclear blast, the subsequent fires would create enormous amounts of soot whose dispersal into the atmosphere would absorb enough of the sun s radiation to create a nuclear winter on Earth. Nevertheless, particulates can be useful. In many industrial furnaces, for example, the presence of carbon particulates increases the radiative power of the flame, and thus can increase appreciably the heat transfer rates. 

We consider an element of the surface of a radiating body, that has a size of dA The energy flow (heat flow) d, emitted into the hemisphere above the surface element, is called radiative power or radiative flow, Fig. 5.2. Its Si-unit is the Watt. The radiative power divided by the size of the surface element... 

The irradiance E combines the incident radiative power of all directions and wavelengths (hemispherical total quantity). 

If, however, (5.33) is integrated over all wavelengths then the absorbed portion of the total radiative power from a solid angle element dw is obtained. This gives... 

We will now consider an enclosure with a body that has any radiation properties, Fig. 5.21. Thermodynamic equilibrium means that this body must also emit exactly the same amount of energy in every solid angle element and in every wavelength interval as it absorbs from the hollow enclosure radiation. It therefore holds for the emitted radiative power that... 

This is the law from G.R. Kirchhoff [5.5] Any body at a given temperature T emits, in every solid angle element and in every wavelength interval, the same radiative power as it absorbs there from the radiation of a black body (= hollow enclosure radiation) having the same temperature. Therefore, a close relationship exists between the emission and absorption capabilities. This can be more simply expressed using this sentence A good absorber of thermal radiation is also a good emitter. 

At a given temperature the black body emits the maximum radiative power at each wavelength and in every direction. It is not possible for any other body at... 

This radiative power also penetrates an (imaginary) spherical surface lying at a distance. Des concentric around the sun, Fig. 5.29. 

An opaque body, with the hemispherical total reflectivity r = 0.15, reflects diffusely. Determine the intensity LIef of the reflected radiation and the absorbed radiative power... 

A very long cylinder is struck by radiation that comes from a single direction, perpendicular to its axis (parallel directed radiation). The surface of the cylinder behaves like a grey radiator with the directional total emissivity = 0.85 cos/ . Calculate the reflected fraction of the incident radiative power. 

The spectral thermal radiative power Exy emitted by a blackbody with wavelength A can be related to the spectral radiation intensity Ix b as derived... 

It must be noted that this radiative power, called the BRN equivalent power, noted here as NEPbr, is frequency-independent and varies with T5/2. Assuming an ideal absorbing medium with e = 1, for A = 1 cm2, T = 300 K and A/ = 1 Hz, NEPbr (cm, 300 K, 1 Hz) is 6 x KT11 W. 

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