20 Pharmaceutical Technology BIOLOGICS AND STERILE DRUG MANUFACTURING 2018 P h a r mTe c h . c o m
Bioreactor Design
A
bioreactor is a stirred tank designed to grow cell culture.
The distribution of oxygen in a bioreactor is one of the
main growth-inf luencing factors, along with ample sup-
ply of nutrients, uniform concentration, and consistent
temperature. Agitators are used in these vessels to distribute the gas,
blend the contents of the tank, and drive mass transfer by reducing
gas droplet size.
Oxygen transfer rate (OTR) is defined in Equation 1:
OTR = k
L
a(C* - C) [Eq. 1]
where
k
L
= mass transfer coefficient of the liquid
a = interfacial area between the gas and liquid
C* = saturated concentration of dissolved gas in the liquid
C = operating concentration of dissolved gas in the liquid.
The mass transfer coefficient and interfacial area are combined to
form k
L
a given that both are system dependent and the interfacial area
is unknown in gas–liquid systems. k
L
a is commonly referred to as the
"mass transfer coefficient" due to the inseparable nature of the two terms.
The k
L
a is calculated according to Equation 2:
k
L
a = A(P⁄ V)
α
f
β
[Eq. 2]
where
A, α, and β = system-dependent coefficients
P/V = agitator power input per unit volume
f = superficial gas velocity = gas f low rate divided by cross-sec-
tional tank area.
Impact of Agitator Design
on Bioreactor Performance
Aaron Strand and Nicolle Courtemanche
Aerobic bioprocesses are
highly dependent upon the
oxygen transfer rate from
sparged to dissolved gas.
The relatively low solubility
of oxygen, however, makes
the choice of mixer impeller
configuration a critical design
factor for the bioreactor
vessel. This article describes
a series of experiments
and computational fluid
dynamics simulations to
detail the effect of mixer
configuration on the
efficiency and effectiveness
of a bioreactor vessel
with respect to blend
time and mass transfer.
Aaron Strand, PE is a senior
research engineer with SPX
FLOW, aaron.strand@spxflow.
com; Nicolle Courtemanche
is a senior application engineer
with SPX FLOW, nicolle.
courtemanche@spxflow.com.
CRAFTSMANSHIP/SHUTTERSTOCK.COM
