4.1. Wall effects during the defluidization–fluidization process
Wall effects on the defluidization–fluidization curves, including
friction between the particles and the walls of the bed, have been
modeled by Jackson [28,37]. A complete description of the model can
be found in the literature [28,37], and the model can be summarized
as follows.
The general momentum equation of a group of static particles
confined bywalls in the presence of a gas percolating can be reduced to:
dσs
dz
= −
ρsgug
vt
ϕ
ð1−ϕÞn
4
Dh
μjσs + ϕρsg: ð3Þ
where σs is the compressive yield stress of the particles, z is the
vertical coordinate of the surface of the bed, g is the gravity, ug is the
interstitial gas velocity, vt is the terminal velocity of the particles, ϕ is