PFR and CSTR Combinations in Series

To this point it has been shown, mainly by illustration, that the performance of a reactor depends on three factors  

A fourth aspect also has to do with the nature of mixing of fluid elements of different 

PF can be used to illustrate extremes described by early mixing and late (or no) mixing. In BMF, mixing of fluid elements of all ages takes place early -at the point of entry. In PF, mixing takes place late -in fact, not at all (in the axial direction). We may then use a combination of two vessels in series, one with BMF and one with 

to model the effect of earliness or lateness of mixing, depending on the sequence, on the performance of a single-vessel reactor. The following two examples explore the consequences of such series arrangements-first, for the RTD of an equivalent single vessel, and second, for the fractional conversion. The results are obtained by methods already described, and are not presented in detail. 

Consider the entry of a small amount of fluid as tracer into the PFR at time t = 0. No tracer leaves the PFR until t = VPF/q0 = fPF, the mean residence time in the PFR, and hence no tracer leaves the two-vessel system, at the exit from the CSTR, during the period 0 sk fpF. As a result, 

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