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Mass Transfer in Multiphase Systems and its Applications Part 20

Tham khảo tài liệu 'mass transfer in multiphase systems and its applications part 20', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Mass Transfer in Bioreactors 749 Volumetric mass-transfer coefficient kLa . The gas flow rate was measured with a Brooks Mass controller 5851E while O2 and CO2 were monitored at the in and outlet with a paramagnetic O2 analyser Sybron 540A and infrared CO2 analyser Sybron Anatek PSA 402 . The volumetric mass transfer coefficient obtained at maximum pellet concentration kLa h-1 was derived from the O2 mass balance in the bioreactor Sano et al. 1974 . O2 uptake rate. Different concentrations of dissolved O2 in the bioreactor were obtained by changing the compositions of the inlet air while keeping agitation speed and volumetric gas flow rate constant. The rate of O2 uptake was determined by measuring the O2 concentrations at the in and outlet and as such kinetics of O2 were obtained without disturbing the system i.e. power supply and gas hold-up Wang and Fewkes 1977 . Mixing time. The model assumed perfect mixing and two methods were used to verify this. First the bioreactor with agitation speed of 700 rpm a temperature of 29oC and an airflow of 1 vvm was filled with 0.1 M NaOH and phenolphthalein as a tracer. Samples were taken every 10 to 15 s at four different depths in the bioreactor A B C D and analysed for absorbance at 550 nm Figure 1 . Second a culture of G. fujikuroi in its maximum growth phase to which dextran blue was added as a tracer was sampled every 10-15 sec at four different depths in the bioreactor and analysed for absorbance at 617.1 nm. Dextran blue was used as it is not affected by pH or by oxide-reduction processes which take place during fermentation. The distribution ages were determined by fitting the normalized equation Levenspiel 1999 A f Adt f dt Jo 0 Q 20 To the dynamics of the tracer with Q f Adt the area under the curve of absorbance. A is absorbance of the tracer and t is time. The mixing grade was determined by 21 m f-A-A -Ì100 LA - A0 Fig. 1. Diagram of the bioreactor 750 Mass Transfer in Multiphase Systems and its Applications 4.3 .