Gas holdup and mass transfer characteristics of carboxymethyl cellulose solutions in a bubble column with a radial gas sparger |
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Authors: | H W Ryu Y K Chang S D Kim |
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Institution: | (1) Department of Chemical Engineering and BioProcess Engineering Research Center, Korea Advanced Institute of Science and Technology, 373-1 Kusung Dong, 307-301 Yusung Gu, Taejon, Korea |
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Abstract: | The gas phase holdup and mass transfer characteristics of carboxymethyl cellulose (CMC) solutions in a bubble column having a radial gas sparger have been determined and a new flow regime map has been proposed. The gas holdup increases with gas velocity in the bubbly flow regime, decreases in the churn-turbulent flow regime, and increases again in the slug flow regime. The volumetric mass transfer coefficient (k
La) significantly decreases with increasing liquid viscosity. The gas holdup and k
La values in the present bubble column of CMC solutions are found to be much higher than those in bubble columns or external-loop airlift columns with a plate-type sparger. The obtained gas phase holdup (
g) and k
La data have been correlated with pertinent dimensionless groups in both the bubbly and the churn-turbulent flow regimes.List of Symbols
a m–1
specific gas-liquid interfacial area per total volume
-
A
d m2
cross-sectional area of downcomer
-
A
r m2
cross-sectional area of riser
-
d
b m
individual bubble diameter
-
d
vs m
Sauter mean bubble diameter
-
D
c m
column diameter
-
D
L m2/s
oxygen diffusivity in the liquid
-
Fr
Froude number, U
g/(g Dc)1/2
-
g m/s2
gravitational acceleration
-
G
a
Galileo number, gD
c
3
2/ 2
app
-
H
a m
aerated liquid height
-
H
c m
unaerated liquid height
-
K Pa · sn
fluid consistency index
-
k
L a s–1
volumetric mass transfer coefficient
-
n
flow behavior index
-
N
i
number of bubbles having diameter d
bi
-
Sc
Schmidt number,
app/( D
L)
-
Sh
Sherwood number, k
L a D
c
2
/DL
-
U
sg m/s
superficial gas velocity
-
U
gr m/s
superficial riser gas velocity
-
V
a m3
aerated liquid volume
-
V
c m3
unaerated liquid volume
- N/m
surface tension of the liquid phase
-
g
gas holdup
-
app Pa · s
effective viscosity of non-Newtonian liquid
-
kg/m3
liquid density
-
ý s–1
shear rate
-
Pa
shear stress |
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Keywords: | |
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