Radiant exitance

M = radiant exitance of the light source used, assuming that the irradiance at the reactor surface is equivalent to the exitance of the lamp in a given sector e = molar absorption coefficient c = concentration of the dissolved substrate... 

Emission Models. Incident models do not make use of all the operating variables, such as radiant power or radiant exitance, diameter, and length of the light source, or dimensions and reflection coefficient of the elliptical cavity mentioned above. Models that describe the space of irradiation on the basis of geometry and process variables are known as emission models. 

Equations (79) and (80) describe the radiant exitance at any point in space and originating from the total volume of the light source. By using geometrical concepts to describe a radiation field in an empty annular reactor (Figure 30), integration limits for the spherical coordinates (p, , fi) are given by Eqs. (81)-(84). 

The Planck theory of blackbody radiation provides a first approximation to the spectral distribution, or intensity as a function of wavelength, for the sun. The black-body theory is based upon a "perfect" radiator with a uniform composition, and states that the spectral distribution of energy is a strong function of wavelength and is pro portional to the temperature (in units of absolute temperature, or Kelvin), and several fundamental constants. Spectral radiant exitance (radiant flux per unit area) is de fined as ... 

The sun is an intense source of corpuscular and electromagnetic radiation. The latter is called solar radiation. The sun is a spherical UV/VIS source with an average radius tgun of 6.9585 x 10 m, an average Earth-sun distance dg.g of 1.4957x10 m and a radiant power Pgu of 3.842x10 W. Therefore, the radiant exitance M of the sun calculates to Bolton, 1999). 

Particular problems of photochemical engineering are related to the scaling-up of photoreactors. This is mainly due to problems of lamp technology related to the variations of the radiant exitance M with the increase of the lamp s geometry and electrical input power. Thus, to carry out a reasonable scaling-up and optimization of photoreactors the radiant exitance M or the radiant density (expressed as the ratio of radiant power P to the arc length I of the lamp in W cm , see Tab. 4-1) of the lamps used must be fixed (Braun et al., 1993 a). This, however, is a challenge for the manufacture of lamps. 

Excitation spectrum Plot of the spectral radiant exitance or of the spectral photon exitance against the frequency (or wavenumber, or wavelength) of excitation. When corrected for wavelength dependent variations in the excitation radiant power this is called a corrected excitation spectrum. 

See also photon exitance, spectral radiant exitance. 

Spectral radiant exitance (M ) The radiant exitance, M, at wavelength X per unit wavelength interval. The SI unit is W m, but a commonly used unit is W nT ... 

In equation (1) K y is referred to as the Stern-Volmer constant Equation (1) applies when a quencher inhibits either a photochemical reaction or a photophysical process by a single reaction. <1>° and M° are the quantum yield and emission intensity (radiant exitance), respectively, in the absence of the quencher Q, while <1> and M are the same quantities in the presence of the different concentrations of Q. In the case of dynamic quenching the constant K y is the product of the true quenching constant kq and the excited state lifetime, t°, in the absence of quencher, kq is the bimolecular reaction rate constant for the elementary reaction of the excited state with the particular quencher Q. Equation (1) can therefore be replaced by the expression (2)... 

An emission spectrum is defined by the International Union of Pure and Applied Chemistry (lUPAC) as a "[p]lot of the emitted spectral radiant power (spectral radiant exitance) or of the emitted spectral photon irradiance (spectral photon exitance) against a quantity related to the photon energy, such as frequency v, wave number a, or wavelength X. When corrected for wavelength-dependent variations in the equipment response it is called the corrected emission spectrum (1)."... 

Stefan-Boltzmann constant (a) - Constant in the equation for the radiant exitance M (radiant energy flux per unit area) from a black body at thermodynamic temperature T, viz. M = aT. [1]... 

Every body whose temperature is above absolute zero emits electromagnetic radiation. The radiant exitance M = /F (4> = radiant flux, F =. surface from which the radiation emanates) and the spectral distribution of this radiation depend on the temperature. For the so-called black-body, which per definitionem absorbs all impinging radiation and converts it into heat, the Boltzmann law makes the radiant exitance M = /F. 

So far, we have only spoken of the ideal black body, with an ab.sorption ratio of f = 1. Real bodies have an absorption ratio of e < 1, whereby e is al.so dependent on the wavelength. Following Kirchhoffs Law, the radiant emittance of a real body is M = f.V/s. in which A/s is the radiant exitance of a black body at the same temperature. 

Figure 12 Radiant exitance Af, and M2 of two bodies with temperatures 7 and 7X and absorp-tances f and et-...

Radiant exitance/radiant emittance M Watt per square meter Wm ... 

This is the key relationship and is the Planck black-body radiation equation. Integration of this equation over all wavelengths yields the total radiant exitance of a blackbody. 

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