Role of wall friction in fluidization and standpipe flow

Fluidization–defluidization experiments have been carried out in beds of three different diameters, using XL glass beads and air as the fluidizing medium. The variation of pressure drop and bed height manifested a hysteretic behavior, which was more pronounced in smaller tubes. Analysis of the results using a one-dimensional model proposed by Jackson revealed that the observed effect of tube diameter may be attributed to wall friction. From this analysis, we extracted a quantitative estimate of the variation of the compressive yield stress of an assembly of particles as a function of particle volume fraction. The standpipe performance data reported by Srivastava et al. [Powder Technol. 100 (1998) 173.] for these glass beads were analyzed on the basis of the estimated compressive yield strength. It was found that the support provided by the standpipe wall could be estimated quantitatively from the standpipe holdup data and the compressive yield strength determined separately from our fluidization–defluidization experiments.