Transition Criteria for Fluidized Beds Revisited

Abstract

Stability of the fluidized beds has been a topic of interest for several decades and a number of transition criteria in the empirical form as well as based on hydrodynamic description of the bed are available in literature. In the present work, two criteria derived using analytical arguments (Foscolo and Gibilaro 1984; Batchelor 1988) are revisited and expressed in terms of three non-dimensional independent variables, namely the density ratio, , superficial gas velocity , and particle diameter . The transition criteria appear as a family of curves in between the dimensionless minimum fluidization and single particle terminal velocities for different values of De, on a classical plane. A set of 70 different observations through experiments and numerical simulation is mapped on to the plane to examine the transition criteria. While both the criteria predict the in-homogeneity of the bed at higher De consistently, at lower De, the small scale perturbation is captured in the criterion proposed by Batchelor (1988) but not by the one defined by Foscolo and Gibilaro (1984); nevertheless, the current work presents the mapping of two analytically derived transition criteria on the classical plane which is complimentary with earlier classifications proposed by Kunni and Levespeil (1991).

Keywords:

• Aggregative
• fluidization
• particulate
• transition

Acknowledgment

We are grateful to Prof P. Sunthar for suggesting the problem and useful discussions.