Question

6.5 A baffled fermenter tank, 5.0 ft (1.525 m) in diameter, which will contain 1600 gal (6.056 m³) of a beet-sugar solution, will be used to produce citric acid by action of the microorganism Aspergillus niger at 25°C. The vessel will be agitated with two 28-in-diameter (0.71-m) flat-blade disk turbines, one located 2 ft (0.61 m) above the bottom of the tank, the other 6 ft (1.83 m) from the bottom, on the same shaft, turning at 92 r/min. Sterilized air will be introduced below the lower impeller at 2.1 ft/min (0.01067 m/s) superficial velocity based on the tank cross-sectional area. The solution sp gr = 1.038, the viscosity 1.4 cP ($1.4 \times 10^{-3}$ kg/m \cdot s). (a) Estimate the agitator power required. Ans.: 5.4 kW. (b) If the air is introduced through five $\frac{1}{2}$-in, schedule 40, open pipes (ID = 0.622 in = 15.8 mm), estimate the power imparted to the tank contents by the air.

          6.5 A baffled fermenter tank, 5.0 ft (1.525 m) in diameter, which will contain 1600 gal (6.056 m³) of
a beet-sugar solution, will be used to produce citric acid by action of the microorganism Aspergillus
niger at 25°C. The vessel will be agitated with two 28-in-diameter (0.71-m) flat-blade disk turbines,
one located 2 ft (0.61 m) above the bottom of the tank, the other 6 ft (1.83 m) from the bottom, on
the same shaft, turning at 92 r/min. Sterilized air will be introduced below the lower impeller at 2.1
ft/min (0.01067 m/s) superficial velocity based on the tank cross-sectional area. The solution
sp gr = 1.038, the viscosity 1.4 cP ($1.4 \times 10^{-3}$ kg/m \cdot s).
(a) Estimate the agitator power required.
Ans.: 5.4 kW.
(b) If the air is introduced through five $\frac{1}{2}$-in, schedule 40, open pipes (ID = 0.622 in = 
15.8 mm), estimate the power imparted to the tank contents by the air.

6.5 A baffled fermenter tank, 5.0 ft (1.525 m) in diameter, which will contain 1600 gal (6.056 m³) of
a beet-sugar solution, will be used to produce citric acid by action of the microorganism Aspergillus
niger at 25°C. The vessel will be agitated with two 28-in-diameter (0.71-m) flat-blade disk turbines,
one located 2 ft (0.61 m) above the bottom of the tank, the other 6 ft (1.83 m) from the bottom, on
the same shaft, turning at 92 r/min. Sterilized air will be introduced below the lower impeller at 2.1
ft/min (0.01067 m/s) superficial velocity based on the tank cross-sectional area. The solution
sp gr = 1.038, the viscosity 1.4 cP (1.4 × 10^-3 kg/m ·s).
(a) Estimate the agitator power required.
Ans.: 5.4 kW.
(b) If the air is introduced through five (1)/(2)-in, schedule 40, open pipes (ID = 0.622 in =
15.8 mm), estimate the power imparted to the tank contents by the air.

Added by Heidi W.

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