Segregation index

Figure 10.15 Segregation index at various rotary speed of propellers or paddles in SCISR and STR. —0.6xl0-3 m3 STR 3.6x10 m3 SCISR.

The definitions of the degree of mixing presented above aim at a local characterization of the mixture homogeneity in the physical space. There also exist more indirect mixing indices. The segregation index J of Danckwerts (12) is one of the most famous ones. It applies to continuous reactors and relies upon the variance of age J = Var oip/Var a>where a is the age of a molecule,... 

Figure 2. Distribution of segregation index Xs in Y = 400 mm plane. CUo is 5 moles/m3 and Xs is expressed in %.

Figure 3. Distribution of segregation index XB in fi = 30° plane. CVo is 5 moles/ nF and Xa is expressed in %.

Figure 4. Segregation index Xa vs. stirring speed N for different stirrers (Cvo, 5 moles/m 3). Key X, 180 mm Y, 410 mm ff, 30° , turbine and X. propeller.

The three reaction equations for determining the segregation index are given together with their abbreviated forms in Table 1.3. 

Xi + X2 Gweo + tlAo and the segregation index could be defined as follows ... 

Barbosa-Canovas et al. (1985) studied segregation tendencies in some food mixtures during vertical and horizontal vibrations and showed that segregation occurs not only in free-flowing powder mixtures, but also in some cohesive powder mixtures. Segregation intensity depends not only on the mixture composition, particle size, and mechanical vibration history, but also on whether the mixture is ordered. Barbosa-Canovas et al. (1985) used the segregation index Sindex after the mixture was subjected to vibration or tapping. 

Fig. 6.5 Segregation index, as defined in Ref. [28], for mixing of aqueous solutions in caterpillar mixers with 800,1200, or 2400 pm channel width and depth [27], The smaller the segregation index, the better is the mixing and the shorter is the mixing time.

Figure 6.3 Effects of stirrer speed and feed location on segregation index in a...

The mixing quality can be expressed in terms of a segregation index (X ) defined in Equation 4.45, which lies between 0 and 1. Xj = 1 corresponds to complete segregation and the segregation X5 =0 is obtained for ideal molecular mixing. 

Thus, the segregation index is = 0.012 for a flow rate of V = 4ml min . The segregation indices for all flow rates are calculated accordingly ... 

The general trend in Example 4.4 shows that with increasing flow rate, the segregation index decreases because of enhanced interaction between liquid elements achieving better mixing (see [27]) (Figure 4.29). 

Figure 4.29 Segregation index as function of flow rate in a microchannei.

If the operating conditions are properly defined to prevent these difficulties, the measured 13 concentrations can be used to quantify in an explicit way the mixing quality. The results are first used to calculate the segregation index Xs, which is related to the concentration of iodine formed. The value of this index Xs lies between... 

As mentioned above, the segregation index is a measure of the influence of hydrodynamics on chemical selectivity. It depends on two phenomena ... 

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