Dispersing zone

Decanters are used to separate liquids where there is a sufficient difference in density between the liquids for the droplets to settle readily. Decanters are essentially tanks which give sufficient residence time for the droplets of the dispersed phase to rise (or settle) to the interface between the phases and coalesce. In an operating decanter there will be three distinct zones or bands clear heavy liquid separating dispersed liquid (the dispersion zone) and clear light liquid. 

Droplet dispersion zone, in liquid atomization, 23 183-184 Droplet mean axial velocity, 23 189 variation of, 23 189... 

Key indicators of alteration and proximity to ore are increased K2O (particularly in the shale component) near complete loss of Na20 increased FeO (particularly in the siltstone-sandstone component) and increased CO2 in shale. These changes reflect the development of iron carbonate (siderite and ankerite) by carbonate introduction and some alteration of existing calcic carbonate in siltstone-sandstone samples. Destruction of albite, absence of chlorite and increased abundance of muscovite due to potassic alteration, are the other major mineral alteration effects in the altered host rocks. Trace elements enriched in the primary dispersion zone are Zn, Pb, Ag, Sb, As, Rb, and TI. Antimony provides the most consistent and extensive trace element dispersion halo around the deposit and is also preserved in most of... 

Baur and Stockmayer (13) have recently observed a low frequency dielectric dispersion zone in liquid poly(propylene) oxide which is dependent upon molecular weight in the manner of Eqs. (2.8) and (2.9). Due to the method of synthesis of their samples, there are only infrequent reversals of dipolar sense along the chain, and the model discussed above... 

The variation with frequency of the sound absorption coefficient, p, which rises to a maximum in the centre of the dispersion zone, is given by... 

Efficiency of starch dispersion can be further improved when an excess quantity of steam is used97 or when the starch is held under pressure in a retention device (tank or coil) before discharge to the atmosphere. Both processes require a flash chamber (cyclone) to remove excess steam and steam relieved by the pressure drop. Excess steam refers to a multiple of the quantity required to reach target temperature and pressure. The quantity of saturated steam to reach a target temperature can be calculated from its heat content, the slurry temperature, the specific heats of starch and water, and the enthalpy of starch gelatinization. The action of excess steam in the dispersion zone between the jet and back-pressure valve causes a shear effect that enhances disintegration of the starch granules. In many applications, a three-fold excess of steam is used. 

Each processing step is linked to the next. Therefore the different steps cannot be considered independently from each other. For example, coloring processes already take place in the plastification zone, the incorporation of fibers added to the melt takes place not only in the designated dispersing zone but also in the discharge zone and in partially filled screw channels. 

Fig. 5.16. A screw-type extruder used in continuous wet granulation of pharmaceuticals — the Rietz Extructor. (Courtesy Rietz Division, Bepex Corporation.) Zone 1, premixing zone 2, paste formation zone 3, intense mixing and dispersal zone 4, orifice discharge for size and mixing control.

In a horizontal decanter, dispersed phase drops are being carried along the decanter by the flow of the continuous phase. If the velocity of the two separated layers is more than a few centimeters per second, the shape of the dispersion zone will be distorted by drag, and there will be entraiiunent of drops [21], Therefore, the Reynolds number for both phases must be limited. The effect of Reynolds number on liquid-liquid separation is shown in Table 6.14. This hmitation on the Reynolds number will also be used for the dispersed phase to determine the decanter diameter. The minimum diameter is 10.0 cm (0.328 ft) because of wall effects [19]. 

Calculate Ho, the dispersion-zone height, from Equation 6.15.10. 

The differences between the miscible CO2 foam process and a stable tertiary miscible solvent process are shown in Figures 2 and 3. In the miscible CO2 foam process, oil mobilization occurs as CO2 partitions into and swells the trapped oil above Sorw allowing it to be displaced by the mobile brine. The carbonated brine in turn is displaced by CO2 foam. In comparison, miscible N2 and LPG do not transfer to oil through solution in the water phase, as CO2 does. Instead of a brine bank, the solvent and oil are separated by a miscible dispersion zone. The brine saturation is not reduced below Swc ... 

In continuous mechanical emulsification systems based on turbulent flow, the power density Py viz. power dissipated per unit volume of the emulsion) and residence time, L, in the dispersing zone have been found to influence the result of emulsification as measured by the mean droplet size 0(3 2 which is called the Sauter diameter . This dependency is in most cases described by the following expression ... 

FIG. 15-63 Batch settling profile showing four regions a top clarified phase, a sedimentation zone, a dense-packed dispersion zone, and a bottom clarified phase. [Reprinted from Jeelani, Fanoussopoulos, and Hartland, Ind. Eng. Chem. Res., 38(2f pp. 493-501 (1999), with permission. Copyright 1999 American Chemical Society. ] Consult the original article for a detailed description. 

A dispersal zone with water streamlets flowing from the fipinal—Vittel area towards Luxembourg and centre of Paris Basin. 

A simplified mathematical description of this three-zone model proved [332], however, that the quantity of material converted in the dispersion zone could be ignored, if the original concentration ratio of A and B was less than 0.1 and the action of micro- and macro-mixing is described by the Damkohler number Da = fczCBo/s and n = 27twD/ qs) (where w is the flow rate D is the dispersion coefficient q is the liquid throughput and s [s ] is the shrinkage rate of the volume element). The model was evaluated with competitive reactions in series and parallel reactions, and was found to be adequately applicable. 

Figure 2. Schematic of an inwardly releasing hemisphere (ot = inner radius). The hatched lines represent the dispersed zone of drug in polymer, and the black represents laminated regions through which release cannot occur. Key top view, t — 0, (left) and side view cross section, t = 0 (right).

Figure 8.10. The boundary between structural stability (flocculation zone) and instability (dispersion zone) as influenced by chemical factors in soils.

Viscoelastic stress analysis of two component systems shows that a broadening of the dispersion zone is to be expected 166,167), even if the disperse phase (filler) is purely elastic 166) and it is not necessary to ascribe different molecular properties to the continuous phase. The simplest way to visualize this mechanical interaction is by the use of phenomenological mechanically equivalent models. The model of Takayanagi (/68) is illustrated in Fig. 16. The elastic solution for this model is easily derived from elementary considerations. By the correspondence principle of viscoelastic stress analysis 169), the viscoelastic solution is obtained simply by substituting complex moduli in place of purely elastic moduli... 

The concept of temporal variations in concentration at the flow-through detector explains why pronounced skewed peaks are often observed in flow analysis, especially with loop-based sample introduction. Taylor assumed that dispersion is symmetric in relation to an observer located at the dispersing zone [55,56], but in practice the recorded peaks are usually characterised by a rise time much shorter than the fall time (see also Fig. 1.3e). This skew effect is explained by the fact that the front and trailing portions of the flowing sample, which relate to the rise time and the fall time, respectively, have different residence times in the manifold and are therefore subjected to different extents of dispersion. 

The solution with the species of interest, usually the sample, is introduced via loop Li into a first carrier stream and the established zone flows through reactor Ri towards a second injection port. After a time interval tzs, an aliquot of the dispersing zone is taken by the second sampling loop... 

Sampling a small portion of a dispersing zone and introducing it into a second carrier stream in order to be re-dispersed is a very efficient... 

Different aliquots with known mean concentrations can be sampled from the dispersed zone of a standard solution, allowing efficient implementation of the standard addition method [24]. Only one standard solution is needed, as emphasised in Section 7.1. 

Fig. 4. Diagram of an inwardly-releasing hemisphere a, is the inner radius, a0 is the outer radius, and R is the distance to the interface between the dissolved region (white area) and the dispersed zone (diagonal lines). Black represents laminated regions through which release cannot occur [from Hsieh et at. (11), reproduced with permission of the copyright owner, the American Pharmaceutical Association],...

The degree of dispersion or dilution in an FIA system is characterized by the dispersion coefficient, D. Let us consider a simple dispersion experiment. A sample solution, contained within the-valve cavity prior to injection, is homogeneous and has the original concentration C° that, if it could be scanned by a detector, would yield a square signal the height of which would be proportional to the sample concentration (Figure 23.7). When the sample zone is injected, it follows the movement of the carrier stream, forming a dispersed zone whose form depends on the... 

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