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Diffuse/direct radiation diffusion

The effect of temperature on the kinetics of the direct radiation method is quite complex. Increase in temperature increases the monomer diffusion rate but also increases transfer and termination reaction rates of the growing chains and reduces the importance of the gel effect. Solubility and radical mobility may also change as the temperature is varied [88,89]. [Pg.510]

Pyrheliometer is an instrument that measures only the direct radiation from the solar disk itself, without bouncing off clouds or the atmosphere. Concentrating solar collectors utilize only this part of the total solar radiation. Its measurement gives an indication of the clearness of the sky. The normal incident pyrheliometer (NIP) measures this form of radiation. A tracker, called the equatorial mount, is used to keep the NIP pointed at the sun. The difference between the NIP and the total pyranometer readings is referred to as the diffuse solar radiation. [Pg.518]

In radiation through the atmosphere, the electromagnetic energy is scattered and absorbed so that part of the radiation is observed to be distributed over the entire sky. The radiation within the sun solid angle is usually considered as direct radiation, but in addition, contains smaller amounts of scattered radiation. The scattering and absorption processes depend both spacially and spectrally upon the atmosphere composition and cloud distribution. It is useful to arbitrarily separate the input radiation to a surface into the direct and diffuse or scattered radiation. Figure 2 indicates the relative spectral magnitudes of each of these components. [Pg.398]

The rate of evaporation of water from such an isolated drop, although governed entirely by diffusion, is not governed entirely by diffusion of water vapor. Latent heat must be supplied during evaporation. The drop cools until this heat is conducted in from the air at a rate equalling the outward diffusion of water vapor. There is no other significant heat source since even if the drop were black, the direct radiation contribution of full sunlight would not be important for drops of this size. [Pg.127]

The radiation flux af fhe wall of radiation entrance (Figure 22) was determined by actinometric measurements (Zalazar et al., 2005). Additionally, the boundary condition for fhis irradiafed wall (x = 0) was obtained using a lamp model with superficial, diffuse emission (Cassano et al., 1995) considering (i) direct radiation from fhe two lamps and (ii) specularly reflected radiation from fhe reflectors (Brandi et al., 1996). Note that the boundary conditions at the irradiated and opposite walls consider the effect of reflection and refraction at the air-glass and glass-liquid interfaces, as well as the radiation absorption by the glass window at low wavelengths (the details were shown for fhe laboratory reactor). The radiation model also assumes that no radiation arrives from fhe top and bottom reactor walls (x-y plane at z = 0 and z = Zr). [Pg.280]

The DVI does not take into account the detailed nature of the process and is based on a fair amount of estimation it can be argued, for instance, that it is not the total amount of dust that matters, but rather the fraction that reaches the stratosphere, particularly as a sulfur compound, and how that content evolves in time also, it is not just the change in direct radiation that has an effect, but the redistribution, in the entire spectrum, of the direct and diffuse radiation, etc. The DVI is an approach to identify and relate the rdevant and measurable parameters it gives a useful insight by associating volcanic and climatic chronologies. In the words of the author this is about as far as one can go towards objectivity in the assessment of past eruptions . In this respect it reflects the state of knowledge on the problem in 1970. [Pg.262]

Solar radiation is incident on the from surface of a thin plate with direct and diffuse components of 300 and 250 W/m, respectively. The direct radiation makes a 30° angle with Ihe normal of the surface. The plate surfaces have a solar absorpi i vity of 0.63 and an emissivity of 0.93. The air temperature is 5°C and the convection heat transfer coefficient is 20 W/m °C. The cf-... [Pg.721]

The solar energy received on a horizontal surface, as shown Figure 3, is composed of direct and diffuse radiation. The weather bureau measurements were made with an Eppley pyrheliometer (6, II), which measured the total radiation falling on a horizontal surface. Since the incident angle of diffuse radiation does not vary with time of day and year as it does with direct radiation, it was necessary to determine each component separately. [Pg.110]

Calculating procedure for the LVRPA. In order to apply equation 6.95 we need to solve the RTE (equation 6.32) for this particular reactor set-up. As shown by Alfano etal. (1995) and Cabrera etal. (1994) the radiation field of this reactor can be modeled with a ID, one-directional radiation model and rather simple boundary conditions (Figure 6.10). Hence, with azimuthal symmetry derived from the diffuse emission at x = 0 ... [Pg.154]

For the case of diffuse illumination, there is a difference in the distance traveled for diffuse light, as opposed to directed light. We may define a new absorption coefficient, K, which is dependent on the actual distance that the light travels through the sheet. This is different from the distance traveled by directed radiation, where the distance traveled is equal to the sample thickness. For diffuse illumination of plane parallel particles, the relationship between the two absorption coefficients is... [Pg.44]

The direct physical measurement of the spectral actinic flux F(X) is not easy, although attempts have been made (Shetter and Muller 1999 Hofzumahaus et al. 1999). Generally, irradiance E(k) (radiation flux per unit area, W nm ) is measured by radiometers, and experiments to compare solar spectral intensity in the field with radiative transfer models have been made in order to convert the spectral irradiance E(X) to F(X). In these analyses, downward actinic flux Fd (A) is obtained by upper-hemispherical integration of observed spectral radiance L(k,9,4>) (radiation flux per solid angle, W sr m nm ), and F (A) is expressed as the sum of the flux of direct radiation Fq (X) and downward diffusive... [Pg.65]

On the contrary, if there are clouds, the discrepancy between flie observation and the model is large in general, and the cause of uncertainty is thought to be the contribution of albedo of clouds. When the actinic flux f tot is divided by direct radiation component Fq, and downward and upward diffusive radiation component Fj, and F, respectively, assuming a Lambertian surface i.e. a virtual completely diffusive surface for which radiance is constant being independent of the direction of observation (isotropic scattering),... [Pg.66]

NIR spectrometry has been used widely for the analysis of agricultural, food and pharmaceutical products. It is a rapid technique and may be adapted to the quality control of process streams as, using fiber optics, remote sampling in industrial environments is possible. One of the most useful NIR methods uses diffuse reflectance to analyze solid materials. The sample, usually as a powder, is placed in an integrating sphere and illuminated from an NIR source that directs radiation onto it. [Pg.247]

For opaque materials, the reflectance p is the complement of the absorptance. The directional distribution of the reflected radiation depends on the material, its degree of roughness or grain size, and, if a metal, its state of oxidation. Polished surfaces of homogeneous materials reflect speciilarly. In contrast, the intensity of the radiation reflected from a perfectly diffuse, or Lambert, surface is independent of direction. The directional distribution of reflectance of many oxidized metals, refractoiy materials, and natural products approximates that of a perfectly diffuse reflector. A better model, adequate for many calculational purposes, is achieved by assuming that the total reflectance p is the sum of diffuse and specular components p i and p. ... [Pg.573]

Evaluation of the AS" s that charac terize an enclosure involves solution of a system of radiation balances on the surfaces. If the assumption is made that all the zones of the enclosure a re gray and emit and reflec t diffusely, then the direct-exchange area ij, as evaluated for the black-siirface pair A and Aj, applies to emission and reflections between them. If at a surface the total leaving-flnx density, emitted phis reflected, is denoted by W (and called by some the radiosity and by others the exitance), radiation balances take the form ... [Pg.576]

Fig. 17-4. Radiation heat balance. The 100 units of incoming shortwave radiahon are distributed reflected from earth s surface to space, 5 reflected from cloud surfaces to space, 20 direct reaching earth, 24 absorbed in clouds, 4 diffuse reaching earth through clouds, 17 absorbed in atmosphere, 15 scattered to space, 9 scattered to earth, 6. The longwave radiation comes from (1) the earth radiating 119 units 101 to the atmosphere and 18 directly to space, and (2) the atmosphere radiating 105 units back to earth and 48 to space. Additional transfers from the earth s surface to the atmosphere consist of latent heat, 23 and sensible heat, 10. Source After Lowry (4). Fig. 17-4. Radiation heat balance. The 100 units of incoming shortwave radiahon are distributed reflected from earth s surface to space, 5 reflected from cloud surfaces to space, 20 direct reaching earth, 24 absorbed in clouds, 4 diffuse reaching earth through clouds, 17 absorbed in atmosphere, 15 scattered to space, 9 scattered to earth, 6. The longwave radiation comes from (1) the earth radiating 119 units 101 to the atmosphere and 18 directly to space, and (2) the atmosphere radiating 105 units back to earth and 48 to space. Additional transfers from the earth s surface to the atmosphere consist of latent heat, 23 and sensible heat, 10. Source After Lowry (4).

See other pages where Diffuse/direct radiation diffusion is mentioned: [Pg.1062]    [Pg.492]    [Pg.508]    [Pg.510]    [Pg.72]    [Pg.1505]    [Pg.423]    [Pg.401]    [Pg.578]    [Pg.272]    [Pg.191]    [Pg.708]    [Pg.722]    [Pg.452]    [Pg.568]    [Pg.158]    [Pg.30]    [Pg.31]    [Pg.61]    [Pg.111]    [Pg.38]    [Pg.21]    [Pg.22]    [Pg.30]    [Pg.187]    [Pg.92]    [Pg.133]    [Pg.286]    [Pg.115]    [Pg.206]    [Pg.208]   
See also in sourсe #XX -- [ Pg.5 , Pg.11 , Pg.12 , Pg.13 , Pg.59 ]




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Diffuse/direct radiation

Diffuse/direct radiation

Diffusion directions

Direct diffusion

Radiation diffuse

Radiation direct

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