ABSTRACT
Segregation is a process that has long been used in industry for the processing and handling of bulk solids. When a granular mixture is shaken vertically under gravity, the grains tend to segregate with the larger particles moving to the top of the bed. This is usually referred as the “Brazil nut effect” (Rosato et al. 1987). There have been many studies discussing the segregation of granular materials in a vibrated bed based on simulation (Rosato et al. 1987; Jullien et al. 1992; Knight et al. 1993; Hong et al. 2001) or experimental tools (Knight et al. 1993; Duran et al. 1994; Mobius et al. 2001). Though universally recognized, the mechanisms of this phenomenon are still poorly understood and so far there is no clear theory for the complex mechanisms. There have been three mechanisms proposed for the segregation in a vibrated granular bed: geometrical reorganization (Jullien et al. 1992), size percolation (Williams, 1963) and convection (Knight et al. 1993; Duran et al. 1994). The interstitial gas also plays an important role in determination of the intruder rise time (Mobius et al. 2001). Contrary to the common observations, a large and light intruder could also sink to the bottom of a deep granular bed (Shinbrot & Muzzio 1998;Yan et al. 2003; Breu et al. 2003). Several theoretical investigations have examined the rise and descent of the larger particles in a vertically vibrated bed (Hong et al. 2001; Shinbrot & Wassgren 2001; Liffman et al. 2001; Rhodes et al. 2003). The effects
of cohesive powders on the segregation phenomena plays a role in many industrial applications, and the flow behavior of cohesive materials has attracted much interest over the past few years. The dynamics of vibrated cohesive powder with the effect of liquid bridges has been investigated numerically (Yang & Hsiau, 2001).
