Spectral emittance

The mechanism of radiative transfer in flares was found to depend on compn, flare diameter and pressure (Ref 69). The flare efficiency calcn is complicated by the drop-off in intensity at increasing altitudes and at very large diameters owing to the lower reaction temps (Ref 11, p 13) and the narrowing of the spectral emittance band (Ref 35). The prediction of the light output in terms of compn and pressure (ie, altitude) is now possible using a computer program which computes the equilibrium thermodynamic properties and the luminance (Ref 104) Flare Formulations... 

As with emissivity, the spectral emittance and the emittance are the same when there is no frequency dependence. 

Rare earth Density Surface tension Viscosity Heat capacity Thermal conductivity Magnetic susceptibility x Electrical resistivity Ava s)" Spectral emittance at = 645 nm ... 

Another approach was chosen at INRiM, using an integrating sphere reflectometry technique in which the sample reflectivity was measured relative to a reference material of known reflectivity. By applying KirchofFs law to the result, the normal spectral emittance cm be determined [84,10]. 

Once the optical parameters are known, the spectral reflectivity can directly calculated, which, in turn, can be used to determine the normal spectral emittance for opaque materials (transmittmice = 0) by using KirchhofTs law of thermal radiation. 

For the thermophysical data of solid and liquid iridium, the following uncertainties should be applied temperatures below 2400 K, 4%, temperatures above 2400 K, 1.7 %, normal spectral emittance, 6%, enthalpy in tfie solid state, 4%, enthalpy in the liquid state, 2.5%, heat of fusion, 8%, isobaric heat capacity, 8%, electrical resistivity at initial geometry solid, 4%, liquid, 3.5%, electrical resistivity including volume expansion solid and liquid, 6%, thermal conductivity, 12%, and finally thermal difliisivity, 16%. 

During high velocity CG/HW tests, samples were heated inductively to temperatures between 1100°C and 2500°C. Temperature measurements ofthe surface were also obtained by one-color and two-color pyrometry. Use of a two-color pyrometer was again employed to evaluate the spectral emittance ofthe oxidizing surface. Temperature gradients within the sample were measured by monitoring the temperature at the root of internal holes drilled to within 2.5 mm of the surface." ... 

Willey, R. R. Results of a round-Robin Measurement of Spectral Emittance in the Mid-Infrared, SPIE Paper No. 307- 20, SPIE, The Hague (1987). 

Wiley, R. R. (1987). Results of a round-robin measurement of spectral emittance in the mid-IR. Proc. S.P.I.E. 10, 807. First comprehensive study of Infragold and other diffuse mid-IR standards. 

The difficulty in applying this formula lies in the determination of the value of the coefficient Ku- The latter depends on the geometry of the radiating body, the temperatures Ti and T2, and the directional characteristics of the radiating surfaces, as well as their spectral emittance, absorptance, and reflectance (i.e., their color ). Obviously, the heat flux depends to a major extent on the empirical coefficient K, which at best can be given only approximately even when the geometry is known and the surface properties are deflned. Heat radiation increases sharply with temperature because the absolute temperature in the formula appears to the fourth power. 

Cudzilo investigated the spectral emittance of various pyrolants including Si/PTFE (S. Cudzilo, private communication). The spectrum is mainly a greybody trace superimposed from a strong CO2 peak at 4.3 xm due to the afterburn of carbon (Figure 9.36). 

Payloads based on boron, PTFE, perchlorates and Viton have been proposed as both flare payloads for spectral flares and spectrally matched igniter compositions [55, 56]. Combustion of these materials yields significant amounts of FBO and CO2, both of which serve as spectral emitters [57] (see Figures 9.37 and 9.38). Typical compositions are given below ... 

According to the Planck theory of black-body radiation, the radiant spectral emittance is given by the formula... 

Find the temperature that corresponds to the wavelength of maximum spectral emittance at 650.0 nm, in the red part of the visible spectmm. 

The spectral emittance is defined as the ratio of the radiant power per unit area leaving the surface of a body at some given wavelength to that leaving a blackbody at the same temperature. The spectral emittance can be determined practically by comparing the observed or apparent surface temperature of a material with that of a blackbody cavity existing in the same material. The normal spectral emittance is a special case in which the viewing direction is normal to the smooth, opaque surface of the crystalline material. Emissivity is a property of the surface of real specimens. 

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