2. ● Fig. 3.1 shows the dimensions of what is called a
“standard” stirred tank bioreactor vessel with
Baffles.
FIG. 3.1. Standard Stirred Tank Bioreactor Geometry [Adopted from
S. Aiba, A.E. Humphrey and N.F. Millis. “Bubble Aeration and
Mechanical Agitation”. In Biochemical Engineering, 2 nd Ed., Academic
3. Geometric Ratios for a Standard Bioreactor
Impeller D /D H /D
Vessel /D H /D W /D No. Baffles
L /D W
i t L t i i i i b i b t
Type
Flat-Blade 0.33 1.0 0.25 0.2 1.0 0.1
4
Turbine
Paddle 0. 3 3 1.0 - 0.25 1.0 0.1
4
impeller
Marine 0.33 1.0 pitch = Di 1.0 0.1
4
Propeller
Where:
Dt = tank diameter,
HL = liquid height
Di = impeller diameter
Hb = impeller distance from bottom of vessel
5. FIG. 3.2 B. Mixing Patterns for Flat-Blade Turbine Impeller. Effect of
Baffles. Liquid agitation in presence of a gas-liquid interface, with
and without wail baffles: (a) Marine impeller and (b) Disk flat-blade
turbines; (c) in full vessels without a gas-liquid interface (continuous
flow) and without baffles.
6. 3.1 Mixing and Power Requirements
for Newtonian Fluids in a
Stirred Tank
FIG. 3.3 NP vs. NRe; the power characteristics are shown by the power
number, NP, and the modified Reynolds number, N Re, of single
impellers on a shaft. [Adopted from S. Aiba, A.E. Humphrey and N.F.
Millis. “Bubble Aeration and Mechanical Agitation”. In Biochemical
Engineering, 2nd Ed., Academic Press, Inc., New York (1973) 174].
7. Fig. 3.3 shows relationship
between NP and
NRe at three different flow regimes:
● Laminar
● Transient
● Fully Turbulent
for three different impeller types:
● Six-bladed flat blade turbine
● Paddle impeller
● Marine Propeller
8. The power number is
given by Equ. 3.1
NP = Pgc/n3Di5ρ………………………
(3.1)
The impeller Reynolds
number is given by Equ. 3.2
NRe = nDi2ρ/µ……………..................
(3.2)
Where:
N = dimensionless Reynolds
