but must be accompanied by the formation of biomass compounds.
Dissolved oxygen requirements and aeration regime simulation. Oxygen
consumption for biomass synthesis of microorganisms has been researched in significant
number of studies [2], the general result being the amount of oxygen per kilogram of
absolutely dry yeast. Such interpretation relates to the matter balance, since absolutely dry
substance makes up 25% of the total mass of yeast. If we proceed from this, then the rate
of oxygen consumption is represented by the equation:
d
dM
M
d
dM
y
g
ox
ox
)
(
25
.
0
=
,
(9)
where
)
(g
ox
M
is the oxygen consumption for the growth of an absolutely dry yeast.
Taking into account the conditions (8) and (9), we get:
k
M
g
ox
067
.
1
25
.
0
)
(
=
.
(10)
Then the known value of k allows us to define:
k
M
g
ox
268
.
4
)
(
=
.
(11)
The above considerations and ratios lead to the logical conclusion that the
possibilities of aeration systems for yeast-growing machines based on oxygen dissolution
rate should be consistent with the dynamics of O
2
consumption by yeast, translated to the
growth rate of biomass or the reduction rate of sugar concentration in the medium. This
balance can be described by the following equation:
(
)
s
kg
c
c
F
k
d
dM
s
m
ox
,
−
=
,
(12)
where
m
k
is the coefficient of mass transfer between the dispersed gas phase and
liquid medium, m/s; F is the surface area of phase separation, m
2
;
s
c
and
c
are the
saturation and mass transfer concentrations respectively.
F
k
m
is the volumetric mass
transfer coefficient:
s
m
F
k
k
m
v
3
,
=
.
(13)
The numerical values of mass transfer coefficients and phase separation surface
depend on such physical parameters of liquid and gas phases as temperature, viscosity,
surface tension, hydrodynamic mode of gas-liquid medium, the conditions of dispersed
gas phase formation, gas retention capacity, ascension rate of gas bubbles, etc.
Likewise, the conditions of dispersed gas phase formation, its flow rate, and the
magnitude of gas retention capacity depend on the geometric parameters of the device and
gas-liquid medium and the energy parameters of delivering gas phase into the liquid. The
speed of ascending and descending sections of the circuits of the gas-liquid mixture
depend on the uniform distribution of the incoming gas flows in horizontal cross-sections
of the device. This results in the velocity of the liquid phase reaching 0.3–0.5 m/s if the
relative velocity of a practically stabilized gas phase (relatively liquid) is 0.25–0.27 m/s.
This means that the absolute velocities of the gas phase flow are close to 0.60–0.75 m/s
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