Identifying Mixing Problems

AIChE Webinar
Originally delivered Jun 9, 2010

In the first webinar in this series, Art Etchells gave an overview of industrial mixing problems and the key variables of interest for design and scaling. In this webinar, we quickly review those variables, and expand on the process objectives identified by Dr Etchells. Participants are encouraged to select a problem of their own to consider as we go through the steps in the presentation.

In the first step, the global process objectives are identified: blending, solids suspension, liquid dispersion, gas dispersion, and/or reaction. These processes may happen over a range of scales, from the scale of the equipment to the scale of reacting molecules. It is the wide range of scales we consider that makes mixing distinct. In the second step, the critical step in each process is pinned down to a dominant scale. In the third step, we consider whether it is a degree of homogeneity, a limiting length scale, or a limiting time scale that will dominate the design discussion.

The webinar also covers the simplest, to the most complex, blending problems. In the simplest blending problems, there is one process objective, and one critical process specification. Blending is a good example of this type of problem, as is solids suspension. In more complex processes, several steps occur simultaneously and several design criteria must be met. Liquid-liquid dispersion with the addition of stabilizer, and homogeneous reactor design for a mixing sensitive reaction are a good examples of this type of process. In the most difficult mixing problems, there is a strong interaction between multiple mixing objectives and process time scales. Examples of these types of processes include reactive crystallization without seeding, aerobic bioreactors, and heterogeneous mixing sensitive reactions.

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