Mixing and Mass Transfer in Industrial Bioreactors

Design of a real reactor for a real process in industrial scale requires much more than the design of the "ideal" reactors. This insight is formulated in empirical relations between key process parameters, such as mass and heat transfer coefficients, and the power input to the process. Mixing becomes an important issue, and from mixing time as a function of the geometry of the reactor and the power input, one derives expressions for the transfer parameters. This chapter collects the most important empirical knowledge about design of mixers to achieve a particular goal. The resulting design formulas are not in any way quantitatively correct, but based on dimensional analysis one is able to extrapolate from small-to large-scale operation. It is shown that linear scale-up may not give the smallest power input for a given mixing objective. The introduction presented is the basis for the visionary scale-up/scale-down design principles.