Solid Radiation Intensity

Solid radiation intensity depends on (a) projected areas seeing other hotter or colder solids and gases, (b) solid particles in the flames (luminous flames), and (c) temperature differences between interacting solids. 

The reaction rate is directly proportional to radiation intensity and, as in most other reactions of solids, increases as the crystallite size is reduced. 

Black-body radiation is the radiation emitted by a black-colored solid material, a so-called black body, that absorbs and also emits radiation of all wavelengths. A black body emits a continuous spectrum of radiation, the intensity of which is dependent on its wavelength and on the temperature of the black body. Though a black body is an idealized system, a real solid body that absorbs and emits radiation of aU wavelengths is similar to a black body. The radiation intensity of a black body, at... 

It is important to note that structural transformations of obtained bamboo-like CNT takes place while IR radiation intensity rises. At T=1200°C bamboo-like CNT are converted to solid carbon spheres with diameter in the range of 50-360 nm and octahedral carbon particles with the size in the range of 300-350 nm (Fig. 5). These nanostructured particles consist of carbon only or they contents Gd nanoparticles incapsulated in spherical or octahedral carbon particles. The mechanism of high temperature structural transformations of bamboo-like CNT still needs research. 

Consider the radiation intensity I(r,Q) within a solid angle d 2... 

Introduction 664 12-2 Thermal Radiation 665 12-3 Blackbody Radiation 667 12-4 Radiation Intensity 673 Solid Angle 674... 

Consider the emission of radiation by a differential area element dA of a surface, as shown in Fig. 12-18. Radiation is emitted in all directions into the hemispherical space, and ihe radiation streaming though the surface area dS is proporiional to the solid angle d(o subtended by dS. It is also proportional to ihe radiating area dA as seen by an observer on dS, wluch varies from a maximum of dA when dS is at the top directly above dA (d = 0 ) to a minimum of zero when dS is at the bottom (0 = 90 ). Therefore, the effective ar ea of dA for emission in the direction of B is the projection of dA on a plane normal to 9, which is dA cos 0. Radiation intensity in a given direction is based on a unit area normal to that direction to provide a comnioii basis for the comparison of radiation emitted in different directions. 

The spectral radiation intensity 6, ). for example, is simply the total radiation intensity I d, ) per unit wavelength interval about A. The spectral intensity for emitted radiation 1a,(A, 0, (f>) can be defined as the rate at which radiation energy dQ, is emitted at the wavelength A in the (0, ) direction per unit area normal to this direction, per unit solid angle about this direction, and it can be expressed as... 

Fig.4 - Time-temperature profiles at the sample centerline for chestnut (dashed lines) and beech (solid lines) wood cylinders exposed to several radiation intensities.

In the absence of any trapping phenomenon, the data of Table XII must be compared to the carrier concentrations in the various types of solids in the absence of radiation. In intrinsic semiconductors, this concentration hardly exceeds 10 g. in very pure germanium, for instance, this value is equal to 2.5 X 10 . In extrinsic semiconductors the majority carrier concentration is generally between 10 and 10 g. the corresponding value for minority carriers is generally much lower and may be as small as 10 . Unless very high radiation intensities are used, it is thus seen that in the absence of trapping phenomenon, the influence of radiation upon the number of carriers can become appreciable only in the case of extrinsic semiconductors in other cases only the concentration of minority carriers is affected. 

With the evaluation of the view factor, in addition to the concepts of radiosity, solid angle, intensity, and emissive power (the last three from Chapter 8), we complete the concepts needed for enclosure radiation problems. Now we proceed to the solution methods for these problems electrical analogy and net radiation. 

---