ABSTRACT
This chapter presents methods to solve problems with one independent variable involving second-order differential equation and third-kind boundary condition. The conditions indicate that at the fluid-solid interfaces, heat flux by convection equals the respective due to conduction. One is interested in determining the temperature profile in the shell material as well as the rate of heat transfer between the external surface and surrounding environment. The numerator represents the potential, and the denominator the three resistances in series for the heat transfer: two due to convection and the center one due to conduction. Therefore, relatively thick layers of ash surround the cores of the particles, and it is likely that at combined condition the ruling resistance would be offered by the shell. Therefore, as soon as it is formed, the layer breaks into small particles, which break free from the original particle.
