Flow follower, circulation time distribution

Cell models. In order to predict chemical conversion in stirred tanks, Patterson and coworkers ( 3, 39 > 40) divided the tank volume into 30 mixing segments connected by specified flowrates Q-jj Nd2. The turbulence level in each segment is characterized by Ls ( dT) and e( d2) (HDM model). Mann and coworkers (148,149) also studied a model where cells (or segments) are connected according to the average flow pattern. Commutation according to a specified probability at each cell s outlet allows a stochastic path to be simulated, for instance for a flow follower. They thus obtained circulation time distributions very similar to experimental ones (135, 140, 141). 

Internal circulation patterns and turbulence. Sasakura et al. (138) and Rachez et al. (139) investigated internal age distributions by means of tracers and proposed representative models of the circulation pattern. Bryant and coworkers (135, 140, 141) and Reuss studied more specifically circulation times in large stirred tanks by using radio flow-followers (aiming at applications for fermenters > 0.5 m ). They showed that circulation times tQ were log-normally distributed ... 

White [23,24] observed the circulatory flow behavior using markers with flow visualization technique in the R-R handed screw and double-flighted rotors mixer (Figure 8). This makes possible measurement of the circulation time as a criteria of mixing. Since the flow visualization experiments have limitations in observing the overall flow motion in the mixer, the following experiment was carried out to determine the distribution of elastomers. 

Oosterhuis et al. (1985) reported a mean circulation time of approximately 12 s in an unaerated 19 m fermenter using a radio pill flow follower. The experimental cumulative CTD associated with this mean is shown in Figure 18-7. This is the distribution of the residence time of the liqnid outside the impeller region. If it is... 

---