Mixing time correlation

The net flow though the reactor will be small compared with the circulating flow caused by the agitator. The existence of the throughput has little influence on the mixing time so that mixing time correlations for batch vessels can be used for CSTRs as well. 

A real continuous-flow stirred tank will approximate a perfectly mixed CSTR provided that tmix h/i and tmix i. Mixing time correlations are developed using batch vessels, but they can be applied to flow vessels provided the ratio of throughput to circulatory flow is small. This idea is explored in Section 4.5.3 where a recycle loop reactor is used as a model of an internally agitated vessel. 

Prochazka and Landau [19] developed a mixing time correlation for a single Rushton turbine impeller in a baffled tank in the standard configuration for NRe > 104 ... 

Figure 8.43 Rapid Quench Device. Biocatalyst E and substrate S are combined in a mixing zone (hatched area) and the mixture ejected along a common outlet tube in order to be combined with quencher Q in another mixing zone. Different mixing times correlate with different reaction times t pre-quenching. Spectroscopic monitoring as a function of t gives first order relaxation curves for analysis.

The form of mixing time correlation developed in equation (9.4) may be compared with empirically based correlations in the following section. 

The mixing time correlations in section 9.3.4 should only be used if the depth, H, of the liquid in the tank is reasonably constant. If the level varies by less than 20% of the usual operating level, then base the size of the jet on the distance from the nozzle to the point on the far wall just below the normal operating level. However, use the maximum operating liquid height to size the jet recycle rate from the mixing time equations. 

For a propellor agitator in a baffled tank, a mixing-time correlation is given by Biggs (B5) and that for an unbaffled tank by Fox and Gex (FI). 

Another mixing time correlation is given in Figure 4-8 for the case of Dj — Z. All curves except the one marked Turbine baffled are for unbaffled tanks. Note that the product of N with the mixing time becomes a constant for large Reynolds numbers. 

Po Re in the laminar regime constant for jet mixing time correlation (= 3.00) power law exponent or flow behavior index number of blades, helical ribbon impeller impeller rotational speed (rps)... 

---