Particle migration

For 100 ixm diameter spheres in water and a 10 mm rheometer gap, the particle density must be within 2% of that of water to prevent settling during typical measurements (1000 s). As pointed out in Chapter 5, gravitational settling will affect torque readings in a concentric cylinder rtieometer much less than in a cone and plate or parallel plate rheometer because in the concentric cylinders gravity normally acts parallel rather than perpendicular to the narrow gap of the rheometer. Thus, typically for concentric cylinders, h 50 mm, versus h = rsinfi 3 mm for cone and plate. 

However, inertia can still create difficulties. Lin et al. (1970) show that when the particle Reynolds number becomes large, inertia can alter the velocity field around the sphere, causing deviations in viscosity measurements  

Concentration distribution across the shear gap for various K values (eq. 10.2.13) in (a) Couette flow and (b) planar Poiseuille (slit) flow. Prom Ho and Leal (1974). 

Even if Re, is small, the stress field around a sphere can interact with the wall, causing it to migrate inward. Ho and Leal (1974) have analyzed this problem extensively for both drag (Couette) and pressure-driven (plane Poiseuille) flow. They show that if the spheres are small enough and the flow rate is low. Brownian motion can keep the particles uniformly distributed. Their criteria for neglecting migration are 

Some experimental viscosity results on dilute suspensions of rigid spheres x, glass 5 fim in zinc iodide glycerin (Manley and Mason, 1954) O. polystyrene aqueous latices, 0.42, 0.87 /xm (Saunders, 1961) v. low shear rate, and A, high shear rate limits for nonaqueous polystyrene latices, 0.16-0.43 urn (Krieger, 1972). 

Elephantiasis, oedema of the lower leg consequent to obstruction of the lymphatic drainage, is endemic in bare-footed subjects in the Cameroons and other regions of Africa. The identification of aluminosilicate clay 

Direct entry of alumina adjuvants through the skin may occur by the use of therapeutic vaccines, with a resultant transient uptake of aluminium in the brain (Redhead et al., 1992). The injection of talc (magnesium silicate)-containing drugs intended for oral consumption has been shown to induce progressive pulmonary fibrosis in drug abusers (Pare etal., 1989). 

Exposure of women to cosmetic talcum powder, has been related to the observed presence of the characteristic phyUosilicate talc particles in normal and in malignant ovary tissue (Henderson etal., 1979). The experimental demonstration in rats of migration of talc particles from the vagina to the ovary, illustrates the potential route of entry into the body (Henderson etal., 1986). 

Although commonly formed from endogenous material, the occurrence of synovial crystals formed following environmental exposure to exogenous agents is indicated by the identification of both aluminium phosphate and aluminium silicate particulates (Netter etal., 1983, 1991). It is noteworthy in this context that arthritic symptoms have been reported following the 

The presence of particles in the brains of experimental rats and humans exposed to asbestos has been reported (Pontefiart and Cunningham, 1973 Auerbach et al., 1980). In experimental studies, particles of Teflon, a reflux paste, enter the brain via intravascular transport when injected into the bladder (Aaronson et al., 1993). Encephalitic reactions to accumulated calcium oxalate crystals in the brain as a result of infusions of glucose surrogate polyol solutions have been described (PciflPcr etal., 1984). Such studies indicate the capacity of particulates to enter the brain and thus pose a potential pathological threat to the functioning of the central nervous system (CNS). 

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Particle diam., i Number of elementary electrical charges, Nq Particle migration velocity, u, ft/sec... 

Type of precipitator Type of dust Gas volume, cu ft/ min Average gas veloc- ity, ft/sec Collecting electrode area, sq ft Over-all collection efficiency, % Average particle migration velocity, ft/sec... 

Process Concept The application of a direct elecdric field of appropriate polarity when filtering should cause a net charged-particle migration relative to the filter medium (electrophoresis). The same direct electric field can also be used to cause a net fluid flow relative to the pores in a fixed filter cake or filter medium (electroosmosis). The exploitation of one or both of these phenomena form the basis of conventional electrofiltration. 

The second method of exploitation occurs when the electric field is of a polarity such that the charged-particle migration occurs away from the filter medium. The contribution to the net-particle velocity of the elec trqphoreticaUy induced flow away from the filter medium is generally orders of magnitude less than the contribution to the net-... 

Particle migration velocity The velocity at which a charged particle moves in a given direction in an electric field. 

All enveloped human vimses acquire their phospholipid coating by budding through cellular membranes. The maturation and release of enveloped influenza particles is illustrated in Fig. 3.8. The capsid protein subunits are transported flom the ribosomes to the nucleus, where they combine with new viral RNA molecules and are assembled into the helical capsids. The haemagglutinin and neuraminidase proteins that project fiom the envelope of the normal particles migrate to the cytoplasmic membrane where they displace the normal cell membrane proteins. The assembled nucleocapsids finally pass out from the nucleus, and as they impinge on the altered cytoplasmic membrane they cause it to bulge and bud off completed enveloped particles flxm the cell. Vims particles are released in this way over a period of hours before the cell eventually dies. 

These findings support the view that during the reaction ions are extracted from the surface of the glass particles, migrate to the aqueous phase where they form the matrix, and leave a silica gel relict. This explains why the glass particles appear to be unattacked when examined under the microscope. The presence of both A1 and P in the cementing matrix and the... 

A. W. Chow, S. W. Sinton, J. H. Iwa-miya, T. S. Stephens 1994, (Shear-induced particle migration in Couette and parallel-plate viscometers NMR imaging and stress measurements. Phys. Fluids 6, 2561. 

S. A. Altobelli, E. Fukushima, L. A. Mondy, T. S. Stephens 1991, (Experimental observations of particle migration in concentrated suspensions — Couette flow),/. Rheol. 35, 773. 

Electrophoresis involves the movement of a charged particle through a liquid under the influence of an applied potential difference. A sample is placed in an electrophoresis cell, usually a horizontal tube of circular cross section, fitted with two electrodes. When a known potential is applied across the electrodes, the particles migrate to the oppositely charged electrode. The direct current voltage applied needs to be adjusted to obtain a particle velocity that is neither too fast nor too slow to allow for errors in measurement and Brownian motion, respectively. It is also important that the measurement is taken reasonably quickly in order to avoid sedimentation in the cell. Prior to each measurement, the apparatus should be calibrated with particles of known zeta potential, such as rabbit erythrocytes. 

The velocity of particle migration, v, across the field is a function of the surface charge or zeta potential and is observed visually by means of an ultramicroscope equipped with a calibrated eyepiece and a scale. The movement is measured by timing the individual particles over a certain distance, and the results of approximately 10-15 timing measurements are then averaged. From the measured particle velocity, the electrophoretic mobility (defined as v/E, where E is the potential gradient) can be calculated. 

Transport processes carry wastes through the subsurface environment and must be considered in a fate assessment if the interaction of partition and transformation processes does not immobilize or alter the hazardous waste. Waste migration can take place either in solution or in solid form (particle migration). 

Physical Parameters Affecting Particle Migration in Porous-Media Flow... 

Injection of highly acid or alkaline wastes has the potential to dissolve some reservoir rock to create channels that would allow more distant transport of small particles. Table 20.11 summarizes the various physical parameters that affect particle migration in porous-media flow. 

Fine particle migration can occur in the absence of water-swelling clays. Migrating fines can include the migrating clays kaolinite, illite, chlorite, and some mixed layer clays and fine silica particles (162,163). Fine particle migration is promoted when the... 

More recently certain quaternary ammonium salt polymers have been claimed to be effective in substantially reducing fine particle migration even in the absence of water-swelling clays (1). However, there is little information readily available concerning... 

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