A generalized empirical description for particle slip velocities in liquidfluidized beds

An empirical equation for calculating the slip velocity of a species in any homogeneous suspension is proposed. The Richardson and Zaki (1954, Trans. Inst. Chem. Engng, 32, 35-53) and Lockett and Al-Habbooby (1973, Trans. Ins t. Chem, Engng 51, 281-292; 1974, Powder Technol., 10, 67-71) equations are special cases of the proposed equation, and arise when all species are of the same density. Therefore, the main value of the proposed equation is in describing the slip velocities of particles in suspensions containing speci es of different density. In this short note results from one experimental s ystem are presented, and shown to be consistent with the model. The model i s also consistent with the explanation used by Moritomi et al. (1982) to ac count for phase inversion in fluidized beds. The model is appealing in its simplicity, and should find favour in the design and control of process equ ipment. The new model predicts the strong segregation effects observed in s uspensions containing particles of different density, and hence represents an immediate improvement on the Lockett and Al-Habbooby equation. Its appli cation is expected to cover all homogeneous suspensions, in which the parti cles are all more dense than the suspension. At this stage its validation h as been limited to low concentrations of dense particles settling through a fluidized bed of low density particles as occurs in a Teetered Bed Separat or, and to phase inversion conditions in fluidized beds. It is hoped that t his note might lead to a much more extensive validation of the model by wor kers using vastly different particle species. (C) 1999 Elsevier Science Ltd . All rights reserved.