Macro-, Meso-, and Micromixing

In reaction engineering, mixing can be rate controlling in the case of very fast reactions. In general the reaction progress or the rate of a chemical reaction (here for the component A) is described by the eqitation 

The first term describes the reduction of concentration fluctuations which are mostly reduced after approximately 10 up to 20 stirrer revolutions in the case of a fully turbulent flow with 10. The second term depends on the limiting step in the microscale eddies and the degree of segregation. Many experimental results have shown that the minimrtm macromixing time (first term) can be 

According to Schafer (Schafer 2001) the macromixing time can be described by the last equation with C acro for a special marine-type impeller, Cmacro = 6.5 for au inclined blade impeller, and = 8.5 for a six-blade 

Dealing with meso- and micromixing things are more complicated because there are several steps of turbulence which can be limiting for the progress of a chemical reaction characterized by the timescale 1 /k.  

If any timescale of mixing is longer than l/k the reaction time mixing is rate controlling. As will be shown later the root v/s is the decisive parameter for meso-and microtnixing with v as the fluid viscosity and s as the local specific power input. Therefore, the point and the kind of the addition of the reactant B play a big role. As a mle the reactant is fed at the point of the maximum specific power input immediate discharge region of the - preferable - blade impeller. 

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For a reactive process, the reactants must be brought into contact by mixing before a reaction can occur. In a motionless mixer in turbulent flow, the pressure drop defines the turbulent energy dissipation rate, which then determines the macro-, meso-, and micromixing rates. 

The importance of mixing in precipitation is generally appreciated but not well understood due to its complexity. The concepts of macro-, meso-, and micromixing are presented, with a particular attention devoted to micromixing. 

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