TITLE: Turbulent two-phase flow in bubble columns and stirred fermenters.

AUTHOR: K. E. Morud.

INST.  AUTHOR: Norges Tekniske Hoegskole, Trondheim.


PUB.  TYPE: Thesis


SOURCE: Department of Energy [DEE],  Feb 94,  101p.  ISBN: 82-7119-617-0



Turbulent two-phase flow and growth of Saccharomyces cerevisiae in bubble columns and stirred vessels have been investigated experimentally and numerically. Mean and turbulent gas velocities are measured using laser/phase Doppler anemometer (LDA/PDA). Total gas fractions are measured by observing the level of the liquid surface. A two dimensional two-fluid model, with a standard k-(epsilon) turbulence model, is used to predict the gas-liquid flow. Impellers and baffles are modeled by introducing source and sink terms in the appropriate momentum equations. Mass balances for biomass, sugar and ethanol are calculated using a Monod type of model for the biomass growth rate. Gas-liquid flow in small, medium and large scale bubble columns at different superficial gas velocities are simulated. The computed gas fractions and mean and turbulent velocities of the small and medium scale columns are compared against literature experiments. A fermentation process in a large scale bubble column is simulated, and concentrations of biomass, sugar and ethanol are compared against experimental data from the literature. Radial, axial and tangential bubble velocities in a 15 liter baffled stirred vessel are measured using LDA anemometer, and the effects of increasing gas flow rates and impeller rotational speeds on mean and turbulent velocities at three levels of the vessel are investigated. Furthermore, the total gas holdups with changing operating conditions are determined. The gas-liquid flow of the 15 liter stirred vessel is simulated with the two-fluid model.  Numerical results are verified against own experimental data. Good agreements between experimental and simulated results are found. Moreover, the flow in a medium scale vessel, equipped with two narrowly spaced impellers, and the flow in a large scale vessel, equipped with four impellers, are also predicted. 57 refs., 51 figs., 7 tabs. (ERA citation 19:025411)