Well-mixed region

Figure 10-7 shows the eoneentrations of R and S and the produet distribution Xg as a funetion of time for the feed loeation just above the impeller. The values are normalized with respeet to the final values. R and S inerease steadily with time. Xg inereases at first, reaehing a loeal maximum just before the speeies are mixed by the impeller. The improved quality of the mixture favors die first reaetion and Xg deereases until it reaehes a loeal minimum. At diis point diere is enough R present to allow the seeond reaetion to oeeur even in relatively well mixed regions, and Xg inereases again until it asymptotieally reaehes a final value. Figures 10-8a tlirough 10-8h show the loeal eoneentrations of speeies A, R, and S as a funetion of time for the 600-1 tank at 100 rpm. 

A stream leaving a well-mixed region, such as a well-stirred tank, has the identical properties as in the system, since for perfect mixing the contents of the tank will have spatially uniform properties, which must then be identical to the properties of the fluid leaving at the outlet. Thus, the concentrations of component i both within the tank and in the tank effluent are the same and equal to Cj], as shown in Fig. 1.11. 

The fractional flow rate, (1 - f) Lu,n> is then also the volumetric flow passing through the well-mixed region of settler phase volume, Vmix. The flows leaving the plug-flow and well-mixed regions, Xsp and Xsmn. respectively, then combine to give the actual exit concentration from the settler, X . 

The model equations for the heavy phase settler region then become for the well-mixed region... 

The liquid volumes in the still, reflux drum and on the column plates are well-mixed regions of uniform composition. 

Fig. E11.4 A shaded axial slice of the screw extruder of volume v, which is assumed to move axially in a plug-like mode. The barrel drags melt from the well-mixed annular region over the flight hack to the annular well-mixed region.

Isotope ratios of Ca, Ti and Si on 37 presolar silicon carbide grains from supernova were examined using the NanoSlMS (Cameca). In aU grains of type X, a large enrichment in Si (up to five times Solar) was detected. This mass spectrometric finding implies that most X grains were formed from well mixed regions in supernova ejects. 

What happens with increasing ED current can be presented mathematically with the aid of a simplified model called the Nernst idealization. This model, which is illustrated in Figure 8.17, is based on the simplifying assumptions of stagnant boundary layers of constant thickness and a well-mixed region in the center of the solution compartment. These idealized boundary-layer conditions are obviously unrealistic, especially in the presence of the spacer screens used in an ED stack, but they allow a simplified approach to an otherwise complex problem. 

As shown, the well-mixed region has a fraction, /i, of the feed entering directly, while a fraction, f, enters it only after traversing the plug-flow region. Derive an expression for F t), i.e. (Ci/Cq), of this unit. 

Most batch processes are drained from the bottom of the vessel, but for continuous processes, removal can be from any well-mixed region. It is good practice to keep feed and exit locations as far apart as possible to prevent short-circuiting. ... 

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