Calculation of the radiative exchange in complicated cases

A further problem in the calculation of radiative exchange is the consideration of the fact that gases only absorb and emit within certain wavelength intervals or bands. Here, sometimes the highly simplified assumption will be made that the gas behaves like a grey radiator. A better model of real radiation behaviour is band approximation. This is extensively discussed in [5.37], p. 549-567 and 607-609. 

In the more realistic calculations of radiative exchange in furnaces and combustion chambers, a non-isothermal gas space has to be considered. H.C. Hottel and A.F. Sarohm [5.48] developed the so-called zone method for this case, cf. also [5.37], p. 647-652. Other procedures for the consideration of the temperature fields in the gas space have been extensively dealt with by R. Siegel and J.R. Howell [5.37], Chapter 15. The application of the Monte-Carlo method is suggested in particular, cf. [5.37] and [5.66], which despite being mathematically complex, produces results without making highly simplified assumptions. 

In technical furnaces the radiation from soot, coal and ash particles has to be considered as well as the gas radiation. Then the scattering of radiation by the suspended particles becomes important, alongside absorption and emission. P. Biermann and D. Vortmeyer [5.67], as well as H.-G. Brummel and E. Kakaras [5.68] have developed models for this. A summary can be found in [5.69] and in [5.37], p. 652-673. The calculations of heat transport in furnaces has been dealt with by W. Richter and K. Corner [5.70] as well as H.C. Hottel and A.F. Sarohm [5.48], 

2 A Lambert radiator emits radiation at a certain temperature only in the wavelength interval (Ai, A2), where its spectral intensity 

3 What proportion AM of the emissive power M of a Lambert radiator falls in the portion of the hemisphere for which the polar angle is / 30°  

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