A constant value of H = −460 kJ/molO2 was used as oxygenic
enthalpy.The power dissipated in the culture can be
estimated from the difference between the total heat removed from
the culture and the metabolically produced heat.
Since we are able to simultaneously measure the electric power
consumption of the ABB servo drive on the impeller shaft, an additional
estimate of the agitation power input can be provided. Both
allow constructing a calibration function considering the power
losses within the drive and the mechanical seal as a function of the
impeller shaft speed. The latter is easier to determine than the heat
transfer and were thus used to measure the power draw during the
kLa experiments.
The entire measurement procedure (kLa as well as power transfer
by the agitation system) was implemented in our process
automation system (Siemens Simatic PCS7) as a recipe (executed
in Simatic Batch) and can automatically be run with various reactor
configurations.