Heat Transfer Processes in the Rotary Kiln Bed

Chapter 8 Heat Transfer Processes in the Rotary Kiln Bed 

These equations formed the basis for the various one-dimensional kiln models that have appeared in the literature (Brimacombe and Watkinson, 1978 Wes et al., 1976 and others). In these models an energy balance on the wall must be included, as well as the kinetic expressions for any reactions. The latter led to a set of mass conservation expressions that must be solved along with the energy equation. For example, if the evaporation of free moisture is controlled by heat transfer, rather than mass transfer, an additional thermal balance on the moisture can be included as 

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Heat transfer in the bed of a rotary kiln is similar to heat transfer in packed beds except that in addition to the heat flow in the particle assemblage of the static structure (Figure 8.3), there is an additional contribution of energy transfer as a result of advection of the bed material itself. The effective thermal conductivity of packed beds can be modeled in terms of thermal resistances or conductance within the particle ensemble. As shown in Figure 8.3 almost all the modes of heat transfer occurs within the ensemble, that is, particle-to-particle conduction and radiation heat transfer as well as convection through the interstitial gas depending upon the size distribution of the material and process temperature. Several models are available in the literature for estimating the effective thermal conductivity of packed beds. 

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