58-12 |
Predicting oxygen transfer in bioreactors. |
K. M. DHANASEKHARAN, Fluent Inc., 10 Cavendish Court, Lebanon, NH 03766 With recent expansion of interest for developing biological processes on an industrial scale, there is a need for generalized methods for design and scale-up for bioreactors. One of the key issues in aerobic bioreactor design is oxygen transfer. The correlations in the literature to study oxygen transfer are extensive but there are no generally agreed upon correlations for different types of bioreactors. Particularly when it comes to custom designs and modifications, there are no general design methods available in the literature. The objective of the current work is develop a generalized approach that is applicable to bioreactors with different geometry, size and process conditions. A predictive generalized approach based on computational fluid dynamics (CFD) is presented here. The fermentation medium and air system is modeled as a two-phase multiphase flow system with a multi-fluid Eulerian model. The secondary bubbly phase is assumed to be composed of different bubble sizes and a population balance type equation is solved for each bubble class with birth and death terms due to breakup and coalescence. Bubble breakup is analyzed in terms of bubble interactions with turbulent eddies. Bubble coalescence is modeled by considering bubble collisions due to turbulence, buoyancy and laminar shear. A fully 3D model was created based on the bioreactor geometry and experimental conditions from Kawase and Hashimoto (1996) to validate the model. Oxygen transfer was predicted using the measures of gas (oxygen) hold-up and volumetric mass transfer co-efficient for varying superficial gas velocities. The predictions were compared with experimental work from Kawase and Hashimoto (1996). The comparison showed good agreement between CFD and experiment on gas hold-up and volumetric mass transfer co-efficient. More and more food ingredients are made by bioprocessing. Bioprocessing will become integral to the development of existing high-value products and the replacement of existing processing methods.
Session 58, Food Engineering: Transport processes and kinetics
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