Contacting particle-fluid

Size, shape distribution Voidage, bulk density, contacts, etc. Fluid flow, particle flow, caking, etc. 

Broadly speaking, for G/S systems, three modes of particle-fluid contacting may be recognized to take place simultaneously as shown in Fig. 43 bubbles containing sparsely disseminated particles, emulsion of densely suspended particles, and defluidized (transient as well as persistent) particles not fully suspended hydrodynamically by the flowing gas. For all intents and purposes, it is desirable to suppress bubbles and to prevent defluidization. 

Thus, the random spatial distribution of the three modes of particle-fluid contacting is transformed into the ordered, temporal sequence of the three stages of the sedigraph. 

Figure 43. The three modes of particle-fluid contacting in G S fluidization.

The interfacial area in the contactor, which is directly related to the solids hold-up, strongly influences the mass transfer rate. To maximise the overall mass-transfer rate per unit volume of equipment, a high solids hold-up is necessary. On the other hand, the solids hold-up also influences the pressure drop over the contactor. The pressure drop has a hydrostatic and a dynamic component, both of which rise with increased solids hold-up. Since the adsorbent consists of extremely small particles, fluid friction between liquid and solids may lead to a relatively high dynamic pressure drop. The hydrostatic pressure drop is attributable to the density difference between the suspension in the contact zone and in the liquid. 

It is thus evident that for processes in which resistance at the particle-fluid interface is the dominant rate-controlling step—when the value of hdp/ks or hDdp/Ds is small—operation near the single-particle region, that is, dilute-phase G/S contacting, is the preferred choice. 

The efficiency of particle-fluid contacting in fluidization, popularly described in terms of the quality of fluidization, has its origin not only in the physical properties of the fluidizing medium and of the solid material of which the particles are composed, but also in the particle characteristics and in the group behavior of the particles while in motion. Particle characteristics include size, size distribution, shape, and surface roughness or texture, while... 

Thus, the random, spatial distribution of the three modes of particle-fluid contacting is transformed into the ordered, temporal sequence of the three stages of the sedigraph. The bed collapsing method has been used, too, for other objectives in studies on fluidization (Rietema, 1967 Morooka et al., 1973). 

Two Fluid Nozzles, the spray is created by contacting two fluids, namely the feed slurry and compressed air. The compressed air provides the atomization energy. The device has the advantage of being relatively simple, uses a simple feed pump and affords a wide particle size distribution. On the minus side however, the consumption of compressed air is relatively high (0.25 - 1.0 lb air/lb feed) and this nozzle is typically limited to small plants. Figure 3.7 illustrates such a device... 

In addition to mass-specific intensity of particle-fluid interaction, volume-specific intensity / is another important criterion for evaluating particle-fluid contacting in a system. From Section IV.B, Wst is itself a measure of volume-specific intensity of particle-fluid interaction, that is,... 

Figure 15 maps the variation of this volume-specific intensity with gas velocity Ut and solids flow rate Gs. The subfigure at the top shows the shadowed cross-section for Gs = 80 kg/(m2s). Maximal Iv corresponds to the most efficient particle-fluid contacting per unit volume, and IFst should be integrated volumetrically to yield the global effectiveness of particle-fluid contacting in a reactor. 

In considering particle-fluid contacting for any global systems, the local values of I m(h, r) need to be averaged ... 

The efficiency of particle-fluid contacting in fluidization, popularly described in terms of the quality of fluidization, has its origin not only in the physical properties of the fluidizing medium and of the solid material of... 

Here the radii of the two colliding particles are termed af and ay the mean velocity gradient inducing contacts by fluid shear is given as G. Other parameters are as defined in Table 1. 

Although contact-based methods have proved useful for biological studies, there is a strong need for contact-free, flow-based methods for precise confinement and manipulation of biomolecules and cells. To this end, a number of contact-free fluid flow-based trapping and manipulation methods have been developed. These methods rely on microvortices, microeddies, stagnation point flows, or stagnant regions within a fluid stream to confine particles for further analysis. 

In a rotoklon process of interacting of gas, liquid and hard phases in which resrrlt the hard phase (dust), finely divided in gas, passes in a fluid is realized. Process of hydro-dynamic interacting of phases in the apparatus it is possible to disjoint sequentially proceeding stages on the following fluid acquisition by a gas flow on an entry in the contact device fluid subdivision by a fast-track gas flow in the contact channel concretion of dispersion particles by liquid drops branch of drops of a fluid from gas in the labyrinth drip pan. 

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