Patterns dispersed flow

The washing of filter cake is carried out to remove liquid impurities from valuable solid product or to increase recovery of valuable filtrates from the cake. Wakeman (1990) has shown that the axial dispersion flow model, as developed in Sec. 4.3.6, provides a fundamental description of cake washing. It takes into account such situations as non-uniformities in the liquid flow pattern, non-uniform porosity distributions, the initial spread of washing liquid onto the topmost surface of the filter cake and the desorption of solute from the solid surfaces. 

As 100% vaporization is approached, there is not sufficient liquid flowing in the system to continuously wet the entire tube wall, and thus dry spots appear. Transition Zone III is characterized by the initial appearance of these dry spots, and Region IV is characterized by a completely dry tube wall and a dispersed flow pattern. Due to the effects of gravity, dry spots... 

Three main flow patterns exist at various points within the tube bubble, annular, and dispersed flow. In Section I, the importance of knowing the flow pattern and the difficulties involved in predicting the proper flow pattern for a given system were described for isothermal processes. Nonisother-mal systems may have the added complication that the same flow pattern does not exist over the entire tube length. The point of transition from one flow pattern to another must be known if the pressure drop, the holdups, and the interfacial area are to be predicted. In nonisothermal systems, the heat-transfer mechanism is dependent on the flow pattern. Further research on predicting flow patterns in isothermal systems needs to be undertaken... 

Kosterin (K3) investigated the effect of tube inclination on flow patterns for air-water systems. As tube inclination increases, the flow patterns become more dispersed tube slope is an important variable at the lower liquid or gas rates. At high gas rates, when annular or dispersed flow normally occurs in horizontal tubes, tube inclination has little effect on flow-pattern. 

In flow of mixtures of the two phases in pipelines, the liquid tends to wet the wall and the gas to concentrate in the center of the channel, but various degrees of dispersion of each phase in the other may exist, depending on operating conditions, particularly the individual flow rates. The main patterns of flow that have been recognized are indicated on Figures 6.7(a) and (b). The ranges of conditions over which individual patterns exist are represented on maps like those of Figures 6.7(c) and (d). Since the concept of a... 

In recent years a great deal of applied research has centered on the study of problems related to the environment and environmental processes. In some of these studies, radiotracers have been used as primary tools to measure the dynamics of many physical and biological processes. In the best studies, the use of radiotracers to measure flow patterns, dispersion, and similar features is closely coupled to tests of theoretical models of the processes involved. This modeling is important because in environmental studies the experimental conditions are difficult to control and, in general, only a few of the many possible conditions in a given experiment will be sampled. Therefore, it is important to have some way (i.e., a model) to correlate experimental results measured under special conditions to general statements regarding an environmental process. 

The pattern of flow through a packed adsorbent bed can generally be described by the axial dispersed plug flow model. To predict the dynamic response of the column therefore requires the simultaneous solution, subject to the appropriate initial and boundary conditions, of the differential mass balance equations for an element of the column,... 

A flow-pattern map comprises dispersed flow, annular flow, slug-dispersed flow and slug-annular flow [278]. The highest specific interface measured amounts to 16 000 m2/m3. A porous surface structure (100 cm2) in the reaction channel can be generated by a sulfurhexafluoride plasma etch process with silicon nitride masking [278],... 

Axial dispersion, D When a band migrates along a column packed with non-porous particles, it spreads axially because of the combination effects of axial diffusion and the inhomogeneity of the pattern of flow velocity in a packed bed. This combination of effects is accounted for by a single term, proportional to the axial dispersion coefficient. It is independent of the mass transfer resistance and of the other contributions of kinetic origin to band broadening. 

Fig. 4.2 Photographs of ionic liquid-water two-phase flow patterns in microchannels, a Plug flow, b Disturbed plug, c Plug and drain, d Intermittent flow, e Dispersed flow. f. Quasi annular flow, g Throat annular flow, h Rivulet annular flow, i Drop flow, j Irregular flow...

Visualization of flow illustrates the pattern of flow in a designed microchaimel geometry which helps in understanding device operation and predicting the particle (and ultimately cell) motion. To visualize flow, fluorescent tracer particles of diameter < 1 pm are used. Tracer particles with such a small diameter have very limited inertial effect on them thus, these particles are evenly dispersed in the flow forming particle cloud. By using an inverted epi-fluorescence microscope, the flow pattern can be observed. Using the vortex-based crmtinuous cell extraction device as example [9], the process... 

In Chapter 2, the design of the so-called ideal reactors was discussed. The reactor ideahty was based on defined hydrodynamic behavior. We had assumedtwo flow patterns plug flow (piston type) where axial dispersion is excluded and completely mixed flow achieved in ideal stirred tank reactors. These flow patterns are often used for reactor design because the mass and heat balances are relatively simple to treat. But real equipment often deviates from that of the ideal flow pattern. In tubular reactors radial velocity and concentration profiles may develop in laminar flow. In turbulent flow, velocity fluctuations can lead to an axial dispersion. In catalytic packed bed reactors, irregular flow with the formation of channels may occur while stagnant fluid zones (dead zones) may develop in other parts of the reactor. Incompletely mixed zones and thus inhomogeneity can also be observed in CSTR, especially in the cases of viscous media. 

Another important parameter that can be measured from the XRD pattern is crystallite size, which can have a significant effect on color strength, opacity, ease of dispersion, flow and rheological behavior of the pigment. 

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