Emissivity of water vapor

FIG. 5-21 Cor rection factor for converting emissivity of water vapor to values of P, and Fj other than 0 to 1 atm respectively. To convert atmosphere-feet to Idlopascal-meters, multiply by 30.89 to convert atmospheres to Idlo-pascals, multiply hy (1.0133)(10 ). 

Where human occupancy or wet process plant is present, the emission of water vapor will occur. Depending on external conditions and building fabric constmction, the attendant potential for excessive ambient humidity or surface condensation may exist. 

B. Leckner, Spectral and Total Emissivity of Water Vapor and Carbon Dioxide, Combustion and... 

They were named zeolite ( boiling stone ) in 1756 by Cronstedt, a Swedish mineralogist, who observed their emission of water vapor when heated. At the other size limit, opals constitute another example of a naturally occurring nanostmctured material. These gems are made up mainly of spheres of amorphous silica with sizes ranging from 150 nm to 300 nm In precious opals, these spheres are of approximately equal size and can thus be arranged in a three-dimensional periodic lattice. The optical interferences produced by this periodic index modulation are the origin of the characteristic iridescent colors (opalescence). 

J/g of heat. This water loss acts to withdraw heat, which would otherwise serve to pyrolyze the polymer, and the resultant emission of water vapor also dilutes and cools combustible volatile fragments emitted from breakdown of the polymer. The residual anhydrous alumina also serves as a thermal barrier. Typical levels of addition are at least 50 parts by weight per 100 parts of polymer. 

Figure 9-8. Emissivity of water vapor at 1 atmosphere total pressure and low partial pressure (11).

Water Vapor The contribution to the emissivity of a gas containing H9O depends on Tc andp L and on total pressure P and partial pressure p . Table 5-8 gives constants for use in evaluating . Allowance for departure from the special pressure conditions is made by multiplying by a correction factor C read from Fig. 5-21 as a function of (p + P) and p ,L. The absorptivity 0t of water vapor for blackbody radiation is evaluated from Table 5-8 but at T instead of Tc and at p LT /Tc instead of p, h. Multiply by (Tc/Ti)° . ... 

Combined Soot W2O, and CO2 Radiation The spectral overlap of H9O and CO9 radiation has been taken into account by the constants for obtaining Ec- Additional overlap occurs when soot emissivity , is added. If the emission bands of water vapor and CO9 were randomly placed in the spectrum and soot radiation were gray, the combined emissivity would be Eg phis , minus an overlap correction g s- But monochromatic soot emissivity is higher the shorter the wavelength, and in a highly sooted flame at 1500 K half the soot emission hes below 2.5 [Lm where H9O and CO9 emission is negligible. Then the correction g s must be reduced, and the following is recommended ... 

Moisture, as emission of water and vapor from the process. 

Hydrogen can be used with vei y little or no pollution for energy applications. When hydrogen is burned in air, the main combustion product is water, with traces of nitrogen oxides. Wlien hydrogen is used to produce electricity in a fuel cell, the only emission is water vapor. 

Photoluminescence of the films (in the absence of water vapor) usually is dominated, as for CdS, by a broad defect emission varying from ca. 1.4 to 1.6 eV. A (close to) band-to-band emission is often also observed, usually (but not always) at a lower intensity than the broad defect emission. In the presence of water vapor, however, the band-to-band emission often dominates. 

The lone electrons of the 0 atom in the H2O molecule can also become part of the electron gas in the metal surface and reduce its work function. So Schaaff (75) observed an increase of the photoelectric emission of platinum in the presence of water vapor. On the other hand an adsorbed layer of H2O molecules on the surface of a thin nickel film decreases the electric resistance of the film (18). 

The effect of aircraft emissions on radiative forcing is summarized in Table 5. The global and annual radiative forcing due to subsonic aviation is calculated to be 0.036 Wm 2, which is larger than the value of 0.029 Wm 2 calculated in Section 2.1 (0.121-0.092 from Table 2), mainly due to the inclusion of water vapor emission here. The combined fleet provides a radiative forcing 0.055 Wm 2. Note that the water vapor emission from supersonic aviation plays an important role, providing 0.031 (=0.05-0.019) and 0.027 (=0.059-0.032) Wm-2 respectively in January and July. The results also show strong latitudinal and seasonal variations. 

FIGURE 3. Left Panels. Stratospheric temperature changes due to changes of water vapor and 0, associated with aircraft emissions for (top) subsonic aviation and (bottom) combined subsonic and supersonic aviation. 

When oxidized in a fuel cell, the only significant emission is water vapor. When combusted in an internal-combustion engine (spark-ignition or diesel) some oxides of nitrogen and peroxides may be produced, depending on the calibration of the fuel system and configuration of the engine. None of the toxic emissions typical of petroleum fuels are present [1.35]. 

The sulfate process has traditionally used batch ore digestion, in which concentrated sulfuric acid is reacted with ilmenite. This reaction is very violent and causes the entrainment of sulfur oxides (SOA) and sulfuric acid in large amounts of water vapor. In an effort to reduce the particulate emissions, scrubbers have been installed at most plants, but these, in turn, have necessitated the treatment of large quantities of scrubbing liquid before discharge. Other waste-disposal problem products are spent sulfuric acid and copperas (FeS04-7H20). 

Radiation from the sun is in part reradiated as long wavelength (infrared) radiation from the Earth s surface and is absorbed by small amounts of water vapor, carbon dioxide, ozone, and other compounds in the atmosphere (Table 9.4). The ability of these components to intercept infrared radiation is shown in Figure 9.3. The upper boundary of the stippled area is the emission of the ocean s surface, whereas the lower boundary is the radiation measured at the distance of satellites. The difference is the net energy absorbed and trapped in the lower atmosphere. On a global average annual basis, this trapped infrared radiation is equal to 153 watts per square meter of the Earth s surface. 

Introduction Flame radiation originates as a result of emission from water vapor and carbon dioxide in the hot gaseous combustion... 

Total Emissivities and Absorptivities Total emissivities and absorptivities for water vapor and carbon dioxide at present are still based on data embodied in the classical Hottel emissivity charts. These data have been adjusted with the more recent measurements in RADCAL and used to develop the correlations of emissivities given in Table 5-5. Two empirical correlations which permit hand calculation of emissivities for water vapor, carbon dioxide, and four mixtures of the two gases are presented in Table 5-5. The first section of Table 5-5 provides data for the two constants b and n in the empirical relation... 

In both cases the empirical constants are given for the three temperatures of 1000,1500, and 2000 K. Table 5-5 also includes some six values for the partial pressure ratios pw/pc of water vapor to carbon dioxide, namely 0, 0.5, 1.0, 2.0,3.0, and . These ratios correspond to composition values of pc / (pc + pw) =1/(1+ pw tyc) of 0, 1/3, 1/2, 2/3, 3/4, and unity. For emissivity calculations at other temperatures and mixture compositions, linear interpolation of the constants is recommended. 

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