INFLUENCE OF BUBBLE-SIZE DISTRIBUTION AT THE BED SURFACE ON ENTRAINMENT PROFILE

Determination of complete fractional entrainment data is essential to improved understanding of the effect of operating variables on entrainment from gas-solids fluidized beds. It has been found that consideration of two flux components, a cluster flux with composition identical to the bed material, which rises to a maximum height determined by its ejection velocity, and an elutriation flux, which remains constant with height above bed, describes the experimentally observed entrainment profiles. Further development of this type of analysis has shown that the exponential expression commonly used to describe the variation of entrainment with freeboard height implies an exponential distribution of bubble sizes at the bed surface. This discovery prompted the derivation of entrainment flux models based on the log-normal and gamma-(gamma) distributions which are usually adopted for describing bubble size distributions in gas-solid fluidized beds. The application of these models to experimental data is discussed.