Hydrodynamics of fluidization using kinetic theory: an emerging paradigm: 2002 Flour-Daniel lecture

Abstract

A critical review of the literature on fluidization using the kinetic theory of granular flow is presented. An equation of state for the particles relating solids pressure to the granular temperature and the solids volume fraction, similar to the van der Waals equation for gases, has been verified experimentally to be reasonably correct. Experiments have also shown that the particulate viscosity expression obtained from the kinetic theory gives the same values as that measured by classical methods. We demonstrated using a kinetic theory based particle image velocity (PIV) meter that there are two kinds of turbulence in fluidization: 1. random oscillations of individual particles, measured by the classical granular temperature and 2. turbulence caused by the motion of clusters of particles, measured by the average particle normal Reynolds stress. These two kinds of turbulence give rise to two kinds of mixing, mixing on the level of a particle and mixing on the level of cluster or bubble. To compute the granular temperature, it must be programmed into the computational fluid dynamics (CFD) codes. The code itself computes the Reynolds stresses, similar to the calculation of single-phase turbulence by direct numerical computation. CFD simulations by several groups throughout the world have shown that the multiphase flow models correctly predict transient and time-averaged behavior of fluidized beds: bubbles, clusters and flow regimes. Two challenge problems in the last decade show the capability of the hydrodynamic models to predict, at least qualitatively, radial and axial profiles before their publication.