Study of the liquid circulation velocity in external-loop airlift bioreactors |
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Authors: | M Gavrilescu R Z Tudose |
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Institution: | (1) Present address: Faculty of Industrial Chemistry Department of Transfer Phenomena and Chemical Engineering Technical University of Iasi, 6600 IASI, Romania;(2) Research Center for Antibiotics, Chemical Pharmaceutical Research Institute, Valea Lupului no. 1, 6647 IASI, Romania |
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Abstract: | Liquid circulation velocity was studied in externalloop air-lift bioreactors of laboratory and pilot scale, respectively for different gas input rates, downcomer-to-riser cross-sectional area ratio, A
D/AR and liquid phase apparent viscosities.It was found that, up to a gas superficial velocity in the riser v
SGR 0.04 m/s the dependency of v
SLR on v
SGR is in the following form: v
SLR = a v
SGR
b
, with the exponent b being 0.40. Over this value of v
SGR, only a small increase in liquid superficial velocity, v
SLR is produced by an increase in v
SGR.
A
D/AR ratio affects the liquid superficial velocity due to the resistance in flow and overall friction.For non-Newtonian viscous liquids, the circulation liquid velocity in the riser section of the pilot external-loop airlift bioreactor is shown to be dependent mainly on the downcomer-to-riser cross-sectional area ratio, A
D/AR, the effective (apparent) liquid viscosity,
eff and the superficial gas velocity, v
SGR.The equation proposed by Popovic and Robinson 11] was fitted well, with an error of ± 20%.List of Symbols
A
D m2
downcomer cross-sectional area
-
A
Rm2
riser cross-sectional area
- a =
coefficient in Eq. (7)
-
b =
exponent in Eq. (7)
-
c
s m–1
Coefficient in Eq. (3)
-
D
D m
downcomer diameter
-
D
R m
riser diameter
-
g m2/s
gravitational acceleration
-
H
D m
dispersion height
-
H
L m
ungassed liquid height
-
K Pa s
n
consistency index
-
K
B =
friction factor at the bioreactor bottom
-
K
F =
friction factor
-
K
T =
friction factor at the bioreactor top
-
V
L m3
liquid volume in the bioreactor
-
V
D m3
liquid volume in downcomer
-
V
R m3
liquid volume in riser
-
v
LDm/s
downcomer linear liquid velocity
-
v
LR m/s
riser linear liquid velocity
-
v
SGR m/s
riser superficial liquid velocity
-
v
SLR m/s
riser superficial liquid velocity
-
s–1
shear rate
-
GD =
downcomer gas holdup
-
GR =
riser gas holdup
-
eff Pa s
effective (apparent) viscosity
-
Pa
shear stress
The authors wish to thank Mrs. Rodica Roman for the help in experimental data collection and to Dr. Stefanluca for the financial support. |
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Keywords: | |
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