Emissivity hemispherical

Integrating the energy emitted over all directions at a particular wavelength gives hemispherical-spectral emissivity. Hemispherical-Spectral Emissivity... 

Integrating the emitted energy over both wavelength and direction and comparing with the similar integrated quantity for a blackbody yields hemispherical total emissivity. Hemispherical Total Emissivity... 

Keywords Solar collectors. Thermal conductivity, hemispherical emissivity, hemispherical absorptivity. Carbon nanotubes. Graphite, bio-polymers... 

E = hemispherical emissive power of a blackbody. f = fraction of blackbody radiation lying below X. 

The emissive power of a surface is the flux density (energy per time-surface area) due to emission from it throughout a hemisphere. If the intensity 7 of emission from a surface is independent of the angle of emission, Eq. (5-iii) may be integrated to showthat the surface emissive power is TC7, though the emission is throughout 2% sr. 

Emittanee and Absorptanee The ratio of the total radiating power of a real surface to that of a black surface at the same temperature is called the emittanee of the surface (for a perfectly plane surface, the emissivity), designated by . Subscripts X, 0, and n may be assigned to differentiate monochromatic, directional, and surface-normal values respectively from the total hemispherical value. If radi-... 

FIG. 5-13 Hemispherical and normal emissivities of metals and their ratio. Dashed lines monochromatic (spectral) values versus r/X. Solid lines total values versus rT To convert ohm-centimeter-kelvins to ohm-meter-kelvins, multiply hy 10"l... 

The emissivity of a material is defined as the ratio of the radiation per unit area emitted from a real or from a grey surface (one for which the emissitivity is independent of wavelength) to that emitted by a black body at the same temperature. Emissivities of real materials are always less than unity and they depend on the type, condition and roughness of the material, and possibly on the wavelength and direction of the emitted radiation as well. For diffuse surfaces where emissivities are independent of direction, the emissivity, which represents an average over all directions, is known as the hemispherical emissivity. For a particular wavelength X this is given by ... 

Whilst the calculation of the radiant heat flux from a gas to an adjoining surface embraces inherent spectral and directional effects, a simplified approach has been developed by Hottel and Manglesdorf 54, which involves the determination of radiation emission from a hemispherical mass of gas of radius L, at temperature 7, ... 

Sulfur dioxide Is formed primarily from the Industrial and domestic combustion of fossil fuels. On a global scale, man-made emissions of SOj are currently estimated to be 160-180 million tons per year. These emissions slightly exceed natural emissions, largely from volcanic sources. The northern hemisphere accounts for approximately 90% of the man-made emissions (13-14). Over the past few decades global SOj emissions have risen by approximately 4%/year corresponding to the Increase In world energy consumption. 

The atmospheric CO2 content increased by about 1 ppmv per year during the period 1959-1978 (Bacastow and Keeling, 1981) with the South Pole Pco increase lagging somewhat behind the Mauna Loa (19.5°N,155.6 "W) data. This difference is consistent with our knowledge of interhemispheric mixing times and the fact that most fossil fuel emissions occur in the northern hemisphere (see also Conway et al, 1994a). 

The aurora borealis is due to the emission of photons by excited-state atoms and molecules in the thermosphere, hi the Northern Hemisphere, the aurora is called the Northern Lights. 

In the individual compartments quasi-steady state is achieved depending on emissions, degradation rates and spatial distribution of DDT. According to the seasonality of the parameters affecting degradation rates, e.g. temperature and oxidant abundance, the compartmental burdens in steady state follow a seasonal cycle. As the sources and consequently most of the DDT mass is located in the northern hemisphere, the cycle is defined by the climate of that hemisphere. Times needed to to achieve quasi staty state in the compartments are equal in the AGG and SAT experiment, as well as amplitude and phase of the burden time series. Vegetation reaches quasi-steady state within 2-4 years, and atmosphere already within 2 years. These... 

Therefore data on anthropogenic and natural emissions in the Asian region are necessary for the assessment of heavy metal pollution in these countries. Pollution of Kazakhstan and Kyrgyzstan by mercury and lead has been initially assessed by means of hemispheric modeling using the available global emission inventories of the considered heavy metals. The outcomes of the assessment are presented in this section. 

Figure 12. Spatial distribution of mercury anthropogenic emission in the Northern Hemisphere (a) and in Kazakhstan and Kyrgyzstan (b) in 1995. Black line in the left figure delineates the EMEP region (Ilyin et al., 2004).

The spatial distribution of lead anthropogenic emissions in the Northern Hemisphere and particularly in Kazakhstan and Kyrgyzstan in 1990 is shown in Figure 15. As is seen the major emission sources were located in Europe. Some significant emissions were also in Eastern Asia and in North America. The total anthropogenic emission of lead in the Northern Hemisphere was about 146 kt/yr, the emissions of lead in Kazakhstan and Kyrgyzstan were 5.8 kt/yr and 0.7 kt/yr, respectively. 

At present there exist two versions of MSCE-POP model a regional version elaborated for the EMEP region with spatial resolution 50 x 50 km and 150 x 150 km, and a hemispheric version with spatial resolution 2.5 x 2.5°. Modelling of POP transport requires information on the physical-chemical properties of considered POPs, their emissions and also meteorological and geophysical data. The model output data are calculated fields of depositions and concentrations in the main environmental media with different spatial resolutions and long-term trends of contamination by various... 

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