Of segregation

Figure 7 IN718 sample with segregation, SQUID-Signal versus rotation angle, scan radius is constant and equal to radial coordinate of segregation. Measurements are performed after demagnetization.

Segregation. The problem of segregation occurs when a bulk soHd composed of different particle sizes or densities separates. The result can be quite serious if uniform density or mixed material is required for a process. 

Another technique is to change the particle size distribution. There are, however, disadvantages. If segregation is occurring by the sifting mechanism, the particles must be almost identical in size before sifting is prevented. Alternatively, the mean particle size can be reduced below 100 p.m, but this size reduction (qv) increases the probabiUty of segregation by the too fine powder mechanisms. 

An alternative to traditional mass flow bin design is to use a patented BINSERT, which consists of a hopper-within-a-hopper below which is a single-hopper section (Fig. 15). The velocity pattern in such a unit is controded by the position of the bottom hopper. A completely uniform velocity profile can be achieved which results in an absolute minimum level of segregation. Alternatively, by changing the geometry at the bottom of the hopper, a velocity profile can be developed in which the center section moves faster than the outside, thus providing in-bin blending of the materials (7). 

Loss of material as dust must be considered as a possible means of segregation and shortld not be aggravated by too strong suction in the dust-collection apparatus. 

FIG. 23-12 Comp arison of RTD models, all with the same variance and skewness. Values of C/Cq of segregated conversion of a first-order reaction with kt = 3 original, 0.1408 gamma, 0.1158 Gauss, 0.1148 GC, 0.1418. 

Welded joints are usually in a state of high residual stress, and this can tear a steel plate apart if it happens to contain layers of segregated impurity. 

Danekwerts [1] gave a set of eriteria to provide a measure of the level of mixing. The seale of segregation measures the size of the... 

Intensity of segregation A measure of the difference in concentration between neighboring clumps of fluid, = C /C (l - C ), where C is the time-averaged concentration and C a is the fluctuating component of concentration A. 

Scale of segregation A measure of the average distance between clumps of the same component in a mixture. 

Segregrated flow Occurs when all molecules that enter together also leave together. A state of segregation is associated with every RTD. Each aggregate of molecules reacts independently of every other aggregate, as in an individual batch reactor. 

Using mass-integration strategies of segregation, recycle, interception and sink/ source manipulation, fresh-water usage can in principle be completely eliminated. Hence, for the same reaction conditions and water losses, tl target for wastewater discharge can be calculated from the overall water balance as follows (Fig. 4.4) ... 

As a result of segreg ion, interception and recycle, we have eliminated the use of fresh water in the scrubber leading to a reduchon of fresh water consumption (and influent to biotreatment) by 6.0kg/s. Therefore, the target for segregation, interception and recycle has been realized. Next, we focus our attention on sink/generator manipulation to remove fresh-water consumption in the steam-jet... 

Figure 7.12 Structural representation of segregation, mixing and direct recycle options.

Figure 7.13 is structural representation of segregation, mixing, and direct recycle candidate strategies for the problem. Each source is split into several frac-tions that can be fed to a sink. The flowrate of the streams passed from source w to sink u is referred to as The terms F, Z", and represent the inlet flowrate, inlet composition, and outlet flowrate of the streams associated with unit u. Since mixing is embedded, there is no need to include the mixing tank (m = 4) or the source that it generates u> = 5) in the analysis. Unless recycle of biotreatment effluent is considered, there is no need to represent the biotreatment sink in Fig. 7.13. However, streams allocated to biotreatment should be represented and their flowrates are referred to as (m = 5 is the biotreatment sink). Finally, fresh water may be used in any unit at a flowrate of Fresh,.

An important parameter characterizing the laminar regime is the intersegment spacing over which the species must diffuse to be able to react. For kinetic control, as opposed to diffusion control of the reaction, this spacing must not exceed a certain scale of segregation given by [53J ... 

Azeotropic refrigerants exhibit some segregation of components at conditions of temperature and pressure other than those at which they were formulated. The extent of segregation depends on the particular azeotrope and hardware system configuration. 

A caliper survey prior to pulling a worn string of tubing will provide a quick means of segregating badly worn lengths for removal. 

---