The voidage function and effective drag force for fluidized beds

Y. T. Makkawi, P. C. Wright

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)


Here, an experimental investigation on the effective drag force in a conventional fluidized bed is presented. Two beds of different particle size distribution belonging to group B and group B/D powders were fluidized in air in a 13.8 cm diameter column. The drag force on a particle has been calculated based on the measurement of particle velocity and concentration during pulse gas tests, using twin-plane electrical capacitance tomography. The validity of the voidage function "correction function", (1 - es)n, for the reliable estimation of the effective drag force has been investigated. The parameter n shows substantial dependence on the relative particle Reynolds number (Rep*), and the spatial variation of the effective static and hydrodynamic forces. It is also illustrated that, a simple correlation for the effective drag coefficient as function of the particle Reynolds number (Rep), expressed implicitly in terms of the interstitial gas velocity, can serve in estimating the effective drag force in a real fluidization process. Analysis shows that, the calculated drag force is comparable to the particle weight, which enables a better understanding of the particle dynamics, and the degree of spatial segregation in a multi-sized particle bed mixture. The analogy presented in this paper could be extended to obtain a generalized correlation for the effective drag coefficient in a fluidized bed in terms of Rep and the particle physical properties. © 2003 Elsevier Science Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)2035-2051
Number of pages17
JournalChemical Engineering Science
Issue number10
Publication statusPublished - May 2003


  • Correction function
  • Effective drag force
  • Gas-solid fluidization
  • Process tomography
  • Solid fraction measurement


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