A stirred-tank fermenter is used to cultivate aerobic microorganisms in aqueous suspension. The aerobic cells require...
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A stirred-tank fermenter is used to cultivate aerobic microorganisms in aqueous suspension. The aerobic cells require dissolved oxygen for respiration, which is supplied by aerating the liquid medium. An important design parameter for specifying the oxygen mass-transfer rate in the fermenter is the volumetric mass-transfer coefficient, kLa. To promote the gas-liquid mass- transfer process and suspend the microorganisms within the liquid medium, a flat-blade disk turbine impeller of diameter 0.30 m rotates at 240 rev/min within a 1.0-m diameter tank of 2.0-m3 liquid volume. The aeration rate to the fermenter is 1.2 m3 of air per min, and the air bubbles are observed to be coalescing. The aerobic fermentation is carried out at 35°C and 1.0 atm system pressure. You may assume that the liquid medium approximates the properties of water. a. Determine the volumetric mass-transfer coefficient (kLa) for O2 in water. Also, provide the aerated power input (Pg) and non-aerated power input (P) to the fermenter. b. Based on your answer in part (a), determine the maximum oxygen mass-transfer rate (the OTR) to the liquid medium in units of moles O2 per minute. Assume that the cells immediately consume the dissolved O2, so that the dissolved oxygen concentration in the liquid medium is essentially zero. In biochemical engineering, this situation is called oxygen mass-transfer limited growth. You may also assume that the interphase mass-transfer process is liquid-phase controlling. The Henry's law constant for the dissolution of O2 in water can be found in Table 25.1. The mole fraction of O2 in air is 0.21. A stirred-tank fermenter is used to cultivate aerobic microorganisms in aqueous suspension. The aerobic cells require dissolved oxygen for respiration, which is supplied by aerating the liquid medium. An important design parameter for specifying the oxygen mass-transfer rate in the fermenter is the volumetric mass-transfer coefficient, kLa. To promote the gas-liquid mass- transfer process and suspend the microorganisms within the liquid medium, a flat-blade disk turbine impeller of diameter 0.30 m rotates at 240 rev/min within a 1.0-m diameter tank of 2.0-m3 liquid volume. The aeration rate to the fermenter is 1.2 m3 of air per min, and the air bubbles are observed to be coalescing. The aerobic fermentation is carried out at 35°C and 1.0 atm system pressure. You may assume that the liquid medium approximates the properties of water. a. Determine the volumetric mass-transfer coefficient (kLa) for O2 in water. Also, provide the aerated power input (Pg) and non-aerated power input (P) to the fermenter. b. Based on your answer in part (a), determine the maximum oxygen mass-transfer rate (the OTR) to the liquid medium in units of moles O2 per minute. Assume that the cells immediately consume the dissolved O2, so that the dissolved oxygen concentration in the liquid medium is essentially zero. In biochemical engineering, this situation is called oxygen mass-transfer limited growth. You may also assume that the interphase mass-transfer process is liquid-phase controlling. The Henry's law constant for the dissolution of O2 in water can be found in Table 25.1. The mole fraction of O2 in air is 0.21.
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Fundamentals Of Momentum Heat And Mass Transfer
ISBN: 9781118947463
6th Edition
Authors: James Welty, Gregory L. Rorrer, David G. Foster
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