Flow follower, circulation time

Solid-Liquid Mass Transfer There is potentially a major effect of both shear rate and circulation time in these processes. The sohds can either be fragile or rugged. We are looking at the slip velocity of the particle and also whether we can break up agglomerates of particles which may enhance the mass transfer. When the particles become small enough, they tend to follow the flow pattern, so the slip velocity necessary to affect the mass transfer becomes less and less available. 

Although this expression may not accurately predict circulation time, and in any case particles do not follow a simple predetermined circuit around the bed, it serves to illustrate the significance of the excess gas velocity in determining particle mixing rates. The excess gas flow rate, proportional to the excess gas velocity, is essentially the bubble flow rate. A greater bubble flow generates more bubbles and therefore... 

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 ... 

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). 

Frequently distinct peaks, corresponding to circulations of the whole fluid, appear, their amplitude being damped within some three to five circulations . Using a disc turbine having six flat blades, located half the liquid depth, and three sizes of baified tanks with up to four turbine sizes for each tank, the following correlation for the circulation time, t, was established in the turbulent flow regime ... 

We can identify short circuits, i.e. the existence of fluid flows quickly circulating in the reactor. In that case, following an instantaneous injection of tracer, the residence time... 

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... 

Extractions can be carried out in dynamic, static, or combination modes. In the dynamic mode, the supercritical fluid continuously flows through the sample in the extraction vessel and out the restrictor to the trapping vessel. In the static mode, the supercritical fluid circulates in a loop containing the extraction vessel for some period of time before being released through the restrictor to the trapping vessel. In the combination mode, a static extraction is performed for some period of time, followed by a dynamic extraction. 

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