(328d) Evaluation Of Polydisperse Kinetic Theories

Benyahia, S. - Presenter, Department of Energy

Powders found in nature and used in industry have wide particle size distributions (PSD). Some powders are not even homogenous: different cuts in a PSD may have different densities as is the case of coal commonly used in industrial transport gasifiers. In this study, several kinetic theories used to model polydisperse systems are evaluated based on comparison with published molecular dynamic data obtained in a simple shear flow. The most accurate theory is then used to model a dilute flow of bidisperse powders in a circulating fluidized bed. Computational results show large particles in the mixture segregate more at the walls of the riser similar to experimental measurements. The mechanism of the preferential lateral segregation of large particles at walls is due to two terms in the solids-solids drag that contain solids number density and granular temperature gradients. Without these terms, the theory predicts segregation of smaller particles at the walls due to solids pressure. This explains why previously published computational results based on other kinetic theories failed to predict the experimentally observed lateral segregation trends.