such a clearly defined flow pattern was, in this case, induced by the liquid cross-flow due
to downcomers position. Figure 1.3 shows good agreement of experimental data with gas
holdup values calculated from Eq.(4) for
(5)Table 1.6 Comparison of gas holdup data for
different plate designs (system air-water)
uoG, m/s G
(^) N=3 N=6
(^) This work Perforated plates (φ=0.04; 0.08) This work Dual-flow plates
0.01 0.049 0.026 0.072 0.030
0.02 0.087 0.052 0.123 0.059
0.03 0.122 0.076 0.170 0.085
0.04 0.154 0.097 0.211 0.110
0.05 0.180 – 0.249 0.132
0.06 0.207 – 0.280 0.152
where values of empirical coefficients K 1 , K 2 and K 3 , obtained for respective numbers of
column stages from experimental data, are summarised in Table 1.5.
In Table 1.6, our experimental results are compared with analogical data obtained by
Poncin et al. (1990) in a six stage column sectionalised by dual-flow plates (φ=0.25, dn =
15 mm). Also compared are the data from the three-stage column obtained at otherwise
identical conditions in the present study and in our former work (Zahradník and
Kaštánek, 1974) at different values of free plate area φ=0.0025 and φ=0.04 or 0.08
respectively. Data given in the table clearly show the superiority of the plate design
employed in this work. Moreover, the values of the plate pressure drop measured at
working conditions in our present study were by 20–50% lower than the data reported at
identical gas and liquid flow rates for dual-flow plates (Poncin et al., 1990).
Volumetric Gas-Liquid Mass Transfer Coefficient
The effect of individual independent variables, uoG, cs, and N on kLaL values is apparent
from the data plotted in Figure 1.4. Within the whole range of experimental conditions,
kLaL increased with increasing number of column stages and decreased with increasing
solids content (again in agreement with the analogous data of Kratochvíl et al. (1985)
from a single-stage bubble column). Unlike gas holdup values, kLaL decreased slightly
with increasing liquid or slurry flow rate. As can be seen from Figure 1.5 a-c, the
relationship between kLaL and gas holdup was, however, independent of the solid phase
concentration. Obviously, this observation implies that, within the whole region of
experimental conditions, the solids content did not influence the mechanism of gas-liquid
mass transfer (and thus even kL values) and the decrease of kLaL with increasing cs could
New methodologies for multiphase bioreactors 1 13