General combined model for the hydrodynamic behaviour of fixed and fluidised granular beds

This work describes the derivation of a general mathematical model applicable to both fixed and fluidised granular beds, operating within the full hydrodynamic spectrum from viscous to inertial flows. The fundamental insight for the derivation of the model is that practical fluidised beds and fixed beds have similar hydrodynamic properties. The validity of the general model is demonstrated for fluid fractions up to 0.90. A crucial development in the general model is the replacement of hydraulic diameter, which has served as the size descriptor of flow paths in most fixed-bed models derived since the advent of the classic Blake-Kozeny equation. The new, replacement expression is based on the physical structure of the cross section of random porous beds. In addition, the general model contains a tortuosity factor, derived from the results of previous works involving computational fluid dynamics, to correct flow path length and fluid velocity. The model is constructed using regression analysis of experimental data from six previous major works and tested against previous models.