Modified Penetration Model for Rotary Kiln Wall-to-Bed Heat Transfer

2 Modified Penetration Model for Rotary Kiln Wall-to-Bed Heat Transfer 

By replacing the time variable with the subtended angle 0 we can rewrite Equation (8.5) and its boundary conditions to include the degree of fill, which is in essence a function of 0. 

The first boundary condition, Equation 8.9a, implies that we are assuming the wall and bed temperatures are equal at the initial point of contact. Also, the mean free path for the gas at the contact wall is sufficiently large that convective heat exchange by the gas is not in local equilibrium with the conduction through the bed. However, radiative heat transfer can play a vifal role within the penetration layer (Perron and Singh, 1991). As we did for the freeboard, the most practical approach is not only to solve the differential equation but to establish a heat transfer coefficient that can be used for practical calculations. The heat transfer coefficient per unit contact area may be written in terms of the overall heat balance using Newton s law of cooling. 

Perron and Singh (1991) solved the governing equations using the dimensionless temperature distribution 

Chapter 8 Heat Transfer Processes in the Rotary Kiln Bed 

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