Existence of Micro- and Macrofluids

The existence of segregation in a real reactor system can be investigated by means of three time constants, fr the relaxation time of a chemical process, fo the time of micromixing, and i, the mean residence time. The relaxation time (6) is a characteristic parameter for reaction kinetics and it is the time required to reduce the relative concentration c /co from 1 to the value e For instance, for a first-order reaction (r, = —kq) in a BR, the 

FIGURE 4.29 yj (tanks in series), yur (maximum-mixed tanks in series), and ysT (segregated tanks in series) at M = 1.00, M = vaCob/(vbCoa) R = kAtcoA h/ AyR = DamkOhler number. 

The micromixing time (fp). that is, the time required for complete backmixing on a molecular level, can be estimated from turbulence theories. Molecular diffusion plays a decisive role in mixing if the molecular aggregates are of the same size as microturbulent eddies, whose sizes are given by the turbulence theory of Kolmogoroflf  

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