Beam solar radiation

Let us consider the particular case of a tube directly illuminated only by beam solar radiation. Graphically this looks like in Figure 16. 

Figure 16 Tubular reactor illuminated by beam solar radiation.

Pyrheliometer - A device that measures the intensity of direct beam solar radiation. 

The sun radiates approximately as a blackbody, with an effective temperature of about 6000 K. The total solar flux is 3.9 x 10 W. Using Wien s law, it has been found that the frequency of maximum solar radiation intensity is 6.3 x 10 s (X = 0.48 /rm), which is in the visible part of the spectrum 99% of solar radiation occurs between the frequencies of 7.5 X 10 s (X = 4/um) and 2 x 10 s (X = 0.15/um) and about 50% in the visible region between 4.3 x 10 s (X = 0.7 /rm) and 7.5 X 10 s (X = 0.4 /Ltm). The intensity of this energy flux at the distance of the earth is about 1400 W m on an area normal to a beam of solar radiation. This value is called the solar constant. Due to the eccentricity of the earth s orbit as it revolves around the sun once a year, the earth is closer to the sun in January (perihelion) than in July (aphelion). This results in about a 7% difference in radiant flux at the outer limits of the atmosphere between these two times. 

FIGURE 11.31 Radiaiion fluxes at the buildirtg facade the solar radiation components (direct or beam, diffuse, and reflected radiation from the ground or other buildings) and the components of the radiation back from the building facade (reflected solar and thermal infrared radiation from the building envelope). 

T he total or global solar radiation has a direct part (beam radiation) and a diffuse part (Fig. 11.31). In the simulation, solar radiation input values must be converted to radiation values for each surface of the building. For nonhorizontal surfaces, the diffuse radiation is composed of (a) the contribution from the diffuse sky and (b) reflections from the ground. The diffuse sky radiation is not uniform. It is composed of three parts, referred to as isotropic, circumsolar, and horizontal brightening. Several diffuse sky models are available. Depending on the model used, discrepancies for the boundary conditions may occur with the same basic set of solar radiation data, thus leading to differences in the simulation results. 

A second characteristic of UV solar radiation is fhat, even for very clear afmospheres, if is composed in similar amounfs of both beam and diffuse radiation (Hulstrom et al., 1985). The first is defined as the radiation arriving directly from the sun, while the second is the solar radiation that has been scattered by gases and aerosols after entering the earth s atmosphere. This second t)/pe of radiafion reaches fhe ground in a more or less diffuse manner that is, with similar intensity from all directions in the sky. In this respect, the situation encountered in solar photocatalytic reactors is quite different from fhe one encounfered in solar fhermal collectors. The latter are able to use the whole solar spectrum, and in that case diffuse radiation accounts for a much smaller fraction of fhe global irradiance. 

They are able to collect both beam and diffuse solar radiation. 

R Because the plant is spherical, the total solar radiation absorbed equals its projected area (jrr2) times the solar flux density perpendicular to the solar beam (1000 W m-2) times the absorbance (0.30). To obtain the average solar radiation absorbed over the plant surface, we divide by the plant s surface area (47rr2). Thus... 

Numerical method for modelling atmospheric O2 photodissociation in the wavelength range 175—200 nm Br atom laser action from photodissociation of IBr by solar radiation. Theoretical and experimental study t Cross-section for Ij photodissociation in seeded supersonic beams by CW Ar laser radiation at 514.5 nm... 

Passive optical techniques exploit the natural illumination in the environment (e.g., thermal radiation from the elements in the scene, the Sun, the cloud itself) to replace the active laser beam. In the infrared spectral region, where CW agents have the most characteristic spectral properties, solar radiation contributes little compared with thermal self-emission. As long as the suspect cloud or surface is not in complete thermal equilibrium with the environment, that is, as long as there is a temperature difference between the target and elements in the scene, there are measurable spectral differences between emissions from elements (pixels) on and off the target. 

Solar radiation level at angles normal to the solar beam and horizontal to the surface of the earth in Tulsa, OK. 

Besides PV cells, solar radiation can also be used in concentrating solar thermal systems or for the photo-electrochemical decomposition of water. Concentrating solar systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. The concentrated light... 

The solar radiation incident on a unit horizontal surface at the top of the atmosphere. It is sometimes referred to as solar irradiance. The latitudinal variation of insolation supplies the energy for the general circulation of the atmosphere. Insolation depends on the angle of incidence of the solar beam and on the solar constant, instantaneous transpiration efficiency... 

Beam Radiation - Solar radiation that is not scattered by dust or water droplets. 

Pyranometer - A device used to measure total incident solar radiation (direct beam, diffuse, and reflected radiation) per unit time per unit area. 

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