Question Statement:
Liquid-phase mass transfer coefficient ( kL) is measured in a stirred tank vessel
using steady-state method by sparging air. Oxygen uptake by the microorganism
is measured. The bulk concentration of O 2 is 10 -4 mol L -1. Solubility of O 2 in
water at 25 ˚C is 10-3 mol L-1.
If the oxygen consumption rate is 9×10 -4 mol L -1 s-1, and interfacial area is
100 m2/m3, the value of kL is __________cm s-1.
.61 Consider a piston-cylinder assembly shown in the figure below. The walls of the
cylinder are insulated. The cylinder contains 1 mole of an ideal gas at 300 K and
the piston is held initially at the position z 1 using a stopper. After the stopper is
removed, the piston suddenly rises against atmospheric pressure (1.013×10 5 Pa)
to the new position z2 where it is held by another stopper.
The heat capacity (Cv) of the gas is 12.5 J mol -1 K-1. The cross-sectional area of
the cylinder is 10-3 m2. Assume the piston is weightless and frictionless.
If zଶ - zଵ = 1 m, the final temperature of the gas (rounded off to nearest integer)
is ___________K.
.62 Consider the growth of S. cerevisiae under aerobic condition in a bioreactor and
the specific growth rate of yeast is 0.5 h-1. The overall reaction of the process is
2C6H12O6 +0.2NH3+10.35O2 CH1.8O0.5N0.2+0.2C2H6O+10.6CO2+10.8H2O
The heat of combustion values for different compounds are tabulated below with
the reference to CO2, H2O, O2, and N2 at standard conditions.
Compound Heat of combustion
(kJ mol-1)
C6H12O6 2802
NH3 383
CH1.8O0.5N0.2 560
C2H6O 1366
The specific rate of heat production (rounded off to nearest integer) is
_____________ kJ mol-1 h-1.
.63 A pilot sterilization was carried out in a vessel containing 100 m 3 medium with
an initial spore concentration of 10 8 spores/ml. The accepted level of
contamination after sterilization is 1 spore in the entire vessel. The specific death
rate constant for the spore is 2 min -1 at 121 ˚C. Assuming no death takes place
during the heating and cooling cycles, the holding time at 121 ˚C (rounded off to
nearest integer) is _____________min.