Some general aspects of mixing

In Oiapter 3 the importance of mixing in chemical reactors was indicated with the defmition of two ideal reactor types the plug flow reactor, in which no mixing takes place at all, and the perfectly mixed continuous reactor, with infinite mixing rates. The concept of mixing itself, however, was not analysed. 

Note that the term mixing in everyday usage has more than one connotation  

In this text we shall only use the term mixing in the third connotation. The other processes are denoted as blending, suspension or dispersion, as the case may be. In the following we shall focus on the mixing of liquids, which is technically very important, and occasionally refer to gas mixing. 

If we want to acquire mixing in a reactor, we have to choose some sort of mechanical device for increasing the circulation of the reactor contents. There are in fact quite a number of technical possibilities, which can be summarized as follows  

The first two types of stirrers create an effective overall circulation in the vessel, the third one does not. They all create shear stresses, resulting in velocity gradients and deformation of the liquid. 

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