Figure 1.2 Dependence of gas holdup
on the number of column stages cs=0:
uoG=0.025 m s−^1 , uoG=0.033 m s−^1 ,
uoG=0.042 m s
− 1, uoG=0.050m s
− 1,
uoG=0.058 m s
− 1, uoG=0.066 m s
− 1;
cs=2.5 wt.%: ∆ uoG=0.025 m s
− 1,
uoG=0.033 m s−^1 , uoG=0.050 m s−^1 ;
cs=5 wt.%: uoG=0.025 m s−^1.
gas holdup decrease in pseudohomogeneous slurries (see e.g. Epstein, 1983).
Accordingly, the negative effect of the solids content on gas holdup has to be ascribed in
our case solely to the coalescence enhancement due to the presence of solid particles at
gas interface. This observation has been in full agreement with our former data from a
single-stage bubble column (Kratochvíl et al., 1985); however, it contradicts the increase
of gas holdup and specific interfacial area with the addition of solids, reported for
pseudohomogeneous suspensions of fine inert particles in the literature (Sada et al., 1986;
Pandit and Joshi, 1986; Khare and Joshi, 1990). The ostensibly controversial information
on the effect of inert microparticles can be possible related to opposite effect of the
particles presence at the interface on bubble coalescence in different bubbling regimes,
i.e. at different levels of micro-scale turbulence at the gas-liquid interface. While the
increase of gas holdup in the presence of fine inert particles has been commonly ascribed
to the hindered bubble coalescence due to the accumulation of particles at the gas-liquid
interface (Pandit and Joshi, 1986; Wilkinson et al., 1992), it can be envisioned that, at a
Multiphase bioreactor design 10