Radiative Heat Transfer among Exposed Freeboard Surfaces

14 Radiative Heat Transfer among Exposed Freeboard Surfaces 

The direct radiation exchange between a freeboard surface zone such as Aj and an area element A,-, that is, exposed wall-to-exposed bed on the circumferential strip may be calculated using the expression 

By summing over all the reflecting surfaces, an expression for the radiative exchange between Aj and involving a single reflection is obtained as 

Extending the analysis to include an additional reflection will yield a net radiative exchange between Aj and Aj as 

Barr et al. (1989) found that the error introduced by accounting for only two reflections was only 3 percent in pilot rotary kilns except the lining material is such that the emissivity is below 0.5. For large rotary kilns, an emissivity of 0.7 is typical for the refractory walls. 

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