Spectral hemispherical

For an opaque surface, the relationship between the spectral hemispherical reflectivity and the spectral hemispherical absorptivity is... 

The hemispherical emissive power E is defined as the radiant flux density (W/m2) associated with emission from an element of surface area dA into a surrounding unit hemisphere whose base is copla-nar with dA. If the monochromatic intensity ( 2, X) of emission from the surface is isotropic (independent of the angle of emission, 2), Eq. (5-101) may be integrated over the 2k sr of the surrounding unit hemisphere to yield the simple relation Ex = nix, where >, = Ex(X) is defined as the monochromatic or spectral hemispherical emissive power. 

In practice, it is usually more convenient to work with radiation properties averaged over all directions, called hemispherical properties. Noting that the integral of the rate of radiation energy emitted at a specified wavelength per unit surface area over the entire hemisphere is spectral emissive power, the spectral hemispherical emissivity can be expressed as... 

Likewise, the spectral hemispherical absorptivity and. spectral hemispherical reflectivity of a surface arc defined as... 

Where n is the refractive index, a is the absorption coefficient from the Lambert-Beer law and JE is the Planck function specifying the spectral hemispherical em/ssivity of a black body ... 

Spectral hemispherical emissivity F Geometric factor for radiation or correction factor for logarithmic mean temperature difference / Working stress... 

The irradiance is positive if the energy flow is into the hemisphere centered on the direction h and negative if the flow is into the opposite hemisphere. Thus, we may define spectral hemispherical irradiances F+ =d E /dAdtdv and F =d E /dAdtdv, so that the spectral net irradiance becomes F = F — F. Integration over all frequencies yields the net irradiance F= dvFy [Wm-2]. 

Measured spectral hemispherical reflectance of uncoated (as received) and Ti02/Si02 double layer coated silicon solar cells. The approximate 7% reflectance at 700 nm results from silver metallization (—7% surface coverage). From Pettit et at. (33). 

Spectral, hemispherical absorbtivity of a surface (—) Onsager phenomenological coefficients (kg s /m )... 

Spectral hemispherical transmittance of samples is measured using a Perkin-Elmer Lambda-9 dual-beam UV-VIS-NIR spectrophotometer with an integrating-sphere attachment. Use of such a device allows the absolute transmittance to be measured as po- ASTM E903. Such spectral measurements can then be eonvolved with an appropriate standard terrestrial spectrum (as specified by ASTM G173) to compute a solar-weighted hemispherical transmittance, T2 (>.=200 nm to 2600 nm), as a meaningful single measure of optical performance. 

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... 

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, ... 

Broadhurst, T. W., and Becker, H. A., Measurement and Spectral Analysis of Pressure Fluctuations in Slugging Beds, Fluidization Technology, Hemisphere Publishing Corporation, New York, 1 63 (1976)... 

ISO 9845-1, Solar energy - Reference solar spectral irradiance at the ground at different receiving conditions - Part 1 Direct normal and hemispherical solar irradiance for air mass 1,5 (available in English only), 1992. 

The idea of photoionization spatial localization of the molecular bonds or chromophore of a large molecule based on a combination of spectrally selective photoionization of a chosen bond or chromophore of the molecule with electron or ion microscopy is shown on Fig. 1 for a particular case of projective microscopy. A hemispherical tip of a needle with a radius of curvature... 

Flow, Springer-Verlag, Berlin, 1990), Canuto, Hussaini, Quarteroni, and Zang (Spectral Methods in Fluid Dynamics, Springer-Verlag, Berlin, 1988), Anderson, Tannehill, and Pletcher (Computational Fluid Mechanics and Heat Transfer Hemisphere, New York, 1984), and Patankar (Numerical Heat Transfer and Fluid Flow, Hemisphere, Washington, D.C., 1980). 

The two distinct types of SDS headgroup packing indicated by the difference spectra are consistent with the spherocylindrical model of rod micelle formation discussed above. The increase in absorbance of the difference bands with increasing salt concentration indicates a continual increase in the number of relatively ordered SDS molecules packing into the cylindrical portion of the micelle, with the subtraction procedure simply eliminating the spectral contributions from the hemispherical endcaps. 

This Is found by integration of the spectral and spacial functions over the spectrum of the radiation and the solid angle over the hemisphere above the surface. The available energy intensity is... 

The geometry of Figure 6 is used to describe the calculations. The total energy flux through a surface due to a spectral radiation intensity Iv is given by integrating the intensity over the hemispherical space and the frequency as... 

Fig. 6. Progressive reduction in global total hemispherical spectral distributions as Air Mass is...

Several national and international consensus standards organizations, such as the American Society for Testing and Materials (ASTM) and the International Standards Organization (ISO) have adopted a reference standard extraterrestrial spectral distri bution (ASTM E490 00a), and terrestrial reference spectral distributions for direct beam and total hemispherical (on a 37° tilted south facing surface) spectra at a pre scribed air mass of 1.5 (ASTM G173 03).2,1011... 

ASTM, Standard Tables for Reference Solar Spectral Irradiance at Air Mass 1.5 Direct Normal and Hemispherical for a 37° Tilted Surface, Standard G177-03. 2003 American Society for Testing and Materials, West Conshohocken, PA. 

FIG. 5-9 Spectral dependence of monochromatic blackbody hemispherical emissive power. 

---