Suspension of fine particles

Early efforts to produce synthetic mbber coupled bulk polymerization with subsequent emulsification (9). Problems controlling the heat generated during bulk polymerization led to the first attempts at emulsion polymerization. In emulsion polymerization hydrophobic monomers are added to water, emulsified by a surfactant into small particles, and polymerized using a water-soluble initiator. The result is a coUoidal suspension of fine particles,... 

Fig. 15. Phenomena that take place as increasing amounts of an immiscible wetting liquid are added to a suspension of fine particles (103).

Liquids of complex structure, such a polymer solutions and melts, and pseudo-homogeneous suspensions of fine particles, will generally exhibit non-Newtonian behaviour, with their apparent viscosities depending on the rate at which they are sheared, and the time for which they have been subjected to shear. They may also exhibit significant elastic... 

The flow problems considered in previous chapters are concerned with homogeneous fluids, either single phases or suspensions of fine particles whose settling velocities are sufficiently low for the solids to be completely suspended in the fluid. Consideration is now given to the far more complex problem of the flow of multiphase systems in which the composition of the mixture may vary over the cross-section of the pipe or channel furthermore, the components may be moving at different velocities to give rise to the phenomenon of slip between the phases. 

BOOTHROYD, R. G. Trans. Inst. Chem. Eng. 44 (1966) T306. Pressure drop in duct flow of gaseous suspensions of fine particles. 

Solids of different densities can be separated by immersing them in a fluid of intermediate density. The heavier solids sink to the bottom and the lighter float to the surface. Water suspensions of fine particles are often used as the dense liquid (heavy-medium). The technique is used extensively for the benefication (concentration) of mineral ores. 

For suspensions of fine particles, or systems containing a significant amount of fines, the suspending fluid can be considered to be homogeneous, with the density and viscosity modified by the presence of the fines. These properties depend primarily on the solids loading of the suspension, which may be described in terms of either the porosity or void fraction (s) or, more commonly, the volume fraction of solids, buoyant force on the particles is due to the difference in density between the solid (ps) and the surrounding suspension (p ), which is... 

Kuhn et alS50> described the electroflotation process which represents an interesting recent development for the treatment of dilute suspensions. Gas bubbles are generated electrolyt-ically within the suspension, and attach themselves to the suspended particles which then rise to the surface. Because the bubbles are very small, they have a high surface to volume ratio and are therefore very effective in suspensions of fine particles. 

It is important to note that suspensions of fine particles tend to behave rather differently from coarse suspensions in that a high degree of flocculation may occur as a result of the very high specific surface of the particles. For this reason, fine and coarse suspensions are considered separately, and the factors giving rise to flocculation are discussed in Section 5.2.2. 

The behaviour of suspensions of fine particles is very considerably influenced by whether the particles flocculate. The overall effect of flocculation is to create large conglomerations of elementary particles with occluded liquid. The floes, which easily become distorted, are effectively enlarged particles of a density intermediate between that of the constituent particles and the liquid. 

Agitation of the fluid. Agitation of the solvent is important because this increases the eddy diffusion and therefore the transfer of material from the surface of the particles to the bulk of the solution, as discussed in the following section. Further, agitation of suspensions of fine particles prevents sedimentation and more effective use is made of the interfacial surface. 

Fibers can be formed from intractable materials such as ceramics and polytetrafluoro-ethylene through extrusion of a suspension of fine particles in a solution of a matrix polymer. The matrix polymer-intractable material is coagulated embedding, aligning the intractable material in the matrix polymer. The filament is then heated decomposing the matrix polymer. During this process, the material is sintered and drawn giving small, often with little flexibility—fibrils. 

The most widely used theory of suspension stability, the DLVO theory, was developed in the 1940s by Derjaguin and landau (1941) in Russia and by Verwey and Overbeek (1948) in Holland. According to this theory, the stability of a suspension of fine particles depends upon the total energy of interaction, Vt, between the particles. Vf has two components, the repulsive, electrostatic potential energy, Vr, and the attractive force, Va, i. e. 

In the case where a liquid suspension of fine particles of radius r (cm) flows along a solid surface at a wall shear rate (s ), the effective diffusivity Dp (cm s ) of particles in the direction perpendicular to the surface can be correlated by the following empirical equation [7] ... 

Dense-media separation coal-cleaning method based on density separation, using a heavy-media suspension of fine particles of magnetite, sand, or clay. Dense medium dense slurry formed by the suspension of heavy particles in... 

Determine the influence of diffusion on a suspension of fine particles in a fluid. Note It may be shown that the force of diffusion (Berg, 1940) amounts to -BT/N)d In Ckt/dh, where B is the gas constant. T the absolute temperature, N... 

You already know that soluble materials completely dissolve in a solvent to form a clear true solution , and the particles of the solute do not separate out from the solution. Also there are, in some situations, materials that form a suspension of fine particles of a solid in a liquid. These are not true solutions and given time the particles slowly separate out, for example, when earth is stirred with water the fine... 

In addition to coal gasification, the formation of coal slurries is another new use of coal. A slurry is a suspension of fine particles in a liquid. Coal must be pulverized and mixed with water to form a slurry. The resulting slurry can be handled, stored, and burned in ways similar to those used for residual oil, a heavy fuel oil from petroleum accounting for 13% of U.S. petroleum imports. One hope is that coal slurries might replace solid coal and residual oil as fuels for electricity-generating power plants. However, the water needed for slurries might place an unacceptable burden on water resources, especially in the western states. 

The advent of the laser has made the generation of diffraction patterns by a suspension of fine particles a relatively easy task. At the same time, the rapid development of computer-processing equipment and specialized photocells has made it possible to process the information in a group diffraction pattern to generate the particle size distribution of the fine particles in suspension. One of the first commercially available... 

If /tpias, = constant, it is a Bingham plastic. This class of materials includes mineral slurries, highly concentrated suspensions of fine particles, meat soup extracts and the activated sludge in waste water purification. If the yield value is first exceeded at a particular shear rate, this is termed Herschel-Buckley viscosity behavior, an example being tomato soup concentrate [36]. 

Photocatalytic oxidation of organic pollutants on TiO2-based materials has been extensively investigated. The catalyst is used in the form of a suspension of fine particles or thin film on robust substrates. Figure 12.2 shows the variation of open-circuit potential with time for TiO2 film electrodes, prepared by anodization of Ti... 

Figure 7.4 Evaporative light scattering detector. At the outlet of the column the mobile phase is nebulized under a stream of nitrogen, by a specially atomizing device. When a compound elutes from the column, the droplets under evaporation give a suspension of fine particles. Illuminated by a laser source they scatter the light from a lamp via the Tyndall effect (what happens is comparable to the diffusion by fog through a car headlight beam). The signal detected by a photo-diode is proportional to the concentration of the compound illuminated. Irrespective of the substance, the response factors are very close. This detector is only useful for sample components that cannot be vaporized in the heated section of this detector.

The principle of crossflow filtration can be applied to concentrate suspensions of fine particles or collodial material or to fractionate solutions of macroraolecules. The term microfiltration is generally used for particles in the size range 0.1 to 5 m. 

Suspensions may contain not just solid particles and water but also emulsified oil and even dispersed gas bubbles. In the large Canadian oil sands mining and processing operations, bitumen is disengaged from the sand matrix in suspensions created in large tumblers. The bitumen is then separated from the suspension by a flotation process in which the flotation medium is a suspension of fine particles that also contains emulsified oil (bitumen) and dispersed air bubbles see Chapter 13). 

Definition of Suspension. The rheology of suspensions deals with how suspensions respond to an applied stress or strain. The term suspension refers, in general, to dispersions of solids in fluids, although the term aerosol is conventionally used to refer to dilute suspensions of fine particles in a gas and the term emulsion is used to identify (concentrated) suspensions of particles in a gas or liquid in the field of fluidization. However, emulsion is conventionally defined as the dispersion of a liquid in another (immiscible) liquid. In a broader sense, emulsions are also considered as suspensions. In this chapter, we deal mainly with suspen-... 

A simple relationship was derived by Einstein [14] to calculate the viscosity of a suspension of fine particles in a fluid, such that... 

---