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Mixing and Scale-up of Stirred Tank Reactors Using Cfd Simulations

John R. Hannon, Chemical & Biological Engineering, Dartmouth College, 8000 Cummings Hall, Hanover, NH 03755, Charles E. Wyman, Chemical and Enviornmental Engineering, University of California at Riverside, College of Engineering Center for Environmental Research and Technology, 1084 Columbia Avenue, Riverside, CA 92507, and Lee R. Lynd, Thayer School of Engineering, Dartmouth College, 8000 Cummings Hall, Hanover, NH 03755.

Scaling up biochemical processes from laboratory scale (1-10 L) to pilot scale (100-1000 L) to industrial scale (10,000 1,000,000+ L) presents a significant engineering challenge because nearly every mixing factor changes. Typical scale-up techniques include maintaining one parameter constant such as 1) impeller tip speed, 2) Reynolds number, 3) mixing time, or 4) the ratio of power number to volume. However, all other factors change, raising questions about changes in performance with scale. Because impeller tip speed is often kept constant to avoid potential shear sensitivity effects on fermentative organisms, a computational fluid dynamic (CFD) model was applied to estimate the effect of this strategy on mixing performance, flow path, and power number differences during scale up. Laboratory, pilot, and industrial scale vessel configurations equipped with four, 90 degree baffles and one 45 degree pitched blade turbine (PBT) impeller were analyzed and compared to flow path data using laser doppler anemometry (LDA) and particle image velocimetry (PIV) at various Reynolds numbers where available in the literature. A CFD simulation will also be presented of an actual industrial scale fermentor described in the literature.