6. Material transfer between a particle and a dense bed

Heat transfer between a reactive particle, immersed in a dense, hot bed, and the external environment, consisting of a dispersion of inert gas-solids, controls its heating, drying, devolatilization and eventual ignition. Then, with the reactive particle at a higher temperature than the bed, heat transfer is established from the particle to the bed.

These heat exchanges are generally associated with a mass transfer, for example, of oxygen gas from the bed to the reactive particle, or of gaseous combustion products from the particle to the bed.

The material flow (in kg/s or mol/s) between a surface S, where the species concentration is C _s , and the outside, with species concentration C _∞ , can be written as :