Viscosity coarse relative

Here, is termed the fine relative viscosity and represents the contribution of the colloidal size particles. It is defined by the ratio of the apparent viscosity of the mixture of suspending liquid plus fine particles, to the viscosity of the suspending liquid, ju,. The quantity, is termed the coarse relative viscosity and is the contribution of the coarse particles to the net relative viscosity. It is defined by the ratio of the apparent viscosity of the coarse suspension, 17, to the apparent viscosity of the fine fraction, 17. ... 

Figure 9.4.1 Relative viscosity of a bidisperse coal slurry made up of a colloidal fine fraction of mean diameter 2.3 /j,m and a noncolloidal coarse fraction of 200—300 m particles of mean diameter about 250 fim as a function of shear rate. The volume fraction of the colloidal particles = 0.30 and of the coarse particles , = 0.52. The solid line is a mean curve through the measured viscosities of the colloidal fraction. The triangles are the experimental points for the measured viscosity for the fine plus coarse mixture. The dashed line is the fine relative viscosity experimental curve redrawn through the data points to illustrate the parallelism. The upward shift of this curve corresponds to a coarse relative viscosity log 77, = 2.13. [After Sengun, M.Z. Probstein, R.F. 1989. Bimodal model of slurry viscosity with application to coal-slurries. Part 2. High shear limit behavior. Rheol. Acta 28, 394-401. Steinkopff Darmstadt. With permission.]...

Recovery of DNAPL is a very slow process that is alfected by those factors encountered with LNAPL (i.e., relative permeability, viscosity, residual hydrocarbon pool distribution, site-specific factors, etc ). Dissolution of a DNAPL pool is dependent upon the vertical dispersivity, groundwater velocity, solubility, and pool dimension. Dispersivities for chamolid solvent are estimated for a medium to coarse sand under laboratory conditions on the order of 1(L3 to 1(H m. Thus, limited dispersion at typical groundwater velocities is anticipated to be slow and may take up to decades... 

Because most shear-thinning fluids, particularly polymer solutions and flocculated suspensions, have high apparent viscosities, even relatively coarse particles may have velocities in the creeping-flow of Stokes law regime. Chhabra(35,36) has proposed that both theoretical and experimental results for the drag force F on an isolated spherical particle of diameter d moving at a velocity u may be expressed as a modified form of Stokes law ... 

Mathesoner al. (M7), show that relatively small amounts of fines added to coarse particles sharply decrease the bed viscosity. Based on this evidence, Zenz (Z4) has calculated an optimum size distribution of fluidized particles (as mentioned in Section II,A, 1). The importance of the apparent viscosity in relation to flow characteristics of the bed has been stressed by Matheson et al. (M7), Rice and Wilhelm (R5), Finnerty et al. (F3), Grace (G13), and others. Matheson et al. (M7) have found that the slugging tendencies of a bed can be expressed in terms of the apparent viscosity. Their results for FCC particles containing 20 wt.% of 46-/nm-diameter fine particles gave fit, equal to 6 x 10" g/cm sec this small bed viscosity agreed with the visible high fluidity of the bed. 

Calcium carbonate fillers are either of ground limestone type or precipitated chalk type. They are inexpensive and have low oil-absorption, which allows considerable freedom in filler levels while keeping the viscosity under control. Relatively coarse particle size fillers ranging from 30 to 100 mesh are used to incorporate high loadings. 

Our probe, a float nearly 10 cm in diameter, is coarse with it, we probe the relatively weak forces that exist between the subunits and the solvent (Figure 1A) or between subunit and subunit (Figure IB), or both. Since a systematic study is not available, we do not know which intermolecular structures are probed by the different methods surface viscosity values differ among the methods (6 Ref. 24, p. 104). 

The bimodal model has also been applied to polydisperse suspensions (Probstein et al. 1994), which in practice generally have particle sizes ranging from the submicrometer to hundreds of micrometers. In order to apply the bimodal model to a suspension with a continuous size distribution, a rational procedure is required for the separation of the distribution into fine and coarse fractions. Such a procedure has not been developed so that an inverse method had to be used wherein the separating size was selected which resulted in the best agreement with the measured viscosity. Again, however, the relatively small fraction of colloidal size particles was identified as the principal agent that acts independently of the rest of the system and characterizes the shear thinning nature of the suspension viscosity. 

It is seen that a considerable viscosity reduction is attained by mixing a hue emulsion with a coarse one, over a wide range of composition (54). However, the effect depends on the relative polydispersity of each emulsion, and it is most spectacular with a narrowly dispersed coarse emulsion and a polydispersed fine emulsion with no overlapping. This technique has been proposed for reducing viscosity in crude oil emulsified transpon (55), or coal slurry Row (56). but it may also be readily applied for producing less viscous cosmetic milks or lotions and pharmaceutical emulsions with high imemal phase ratio. 

We stated above that for most applications the slurry behaves as a fluid of modified density, and that viscosity effects can usually be neglected. However, there is a limit to the permissible solids concentration. Relatively coarse solids can simply not be carried in suspension above a certain solids concentration for the particular slurry, say 40 per cent by mass. In the case of very fine solids, a thixotropic mixture is reached at higher solids concentration, in which the solid particles stay in suspension but the slurry viscosity is markedly increased. In fact the viscosity no longer exhibits a Newtonian relationship of direct proportionality between shear stress and velocity gradient. This is an area to keep away from in normal plant design, but for special applications like mine backfill plants, when high solids concentration is critical, it may be desirable to commission a special design based on materials... 

The type and amount of filler have an effect on shrinkage and sink marks more filler reduces both, but at the same time increases the mixture viscosity, which is critical when working with moulding compounds. A combination of coarse and fine particles produces the optimum results. Fillers, such as clay, calcium carbonate and wollastonite, judiciously selected and in relatively high concentrations, can also impart flame retardancy and serve as a stress transfer medium, as well as reduce the total material cost. It should be pointed out that fillers strongly influence the flow characteristics of moulding compounds. 

In summary, ultrasonication facilitates the dispersion of colloidal suspensions at relatively high stress intensities. It relies on the presence of cavitation and on a deep penetration of the sound field into the suspension. The latter is guaranteed by low suspension viscosities (e.g. as for aqueous media with low solid content). A particular problem is the abrasion of the sonotrode tip, which depends on the solid phase, the particle size and shape, the sound intensity, as well as on the abrasion history of the tip. Abrasion particles from sonotrodes are coarse particles in the micrometre range and may spoil the quality of colloidal suspensions. 

Fig. 5.7 Relative changes during the ultrasonication of fumed silica (125 myg, 10 wt%) left average particle size from DLS and LD, turbidity at 400 nm wavelength and dynamic viscosity at shear rate of 1/s right corresponding evolution of the coarse particle concentration as measured by OPC cf. Nogowski et al. (2010)...

As early as 1949, Matheson et al. reported that the addition of relatively small amounts of fines to a coarse bed will decrease the viscosity of the bed substantially. It remained for Trawinski (1953) to find an analytical explanation for this phenomenon. He assumed that the viscosity in a fluidized bed is primarily due to the rubbing of coarse particles among one another. The addition of fines will reduce the friction between coarse particles by coating a thin layer of fines on each coarse particle and thus decrease the viscosity of a fluidized... 

Clarke [81] observed that mixed suspensions of mainly coarse particles and relatively few fine particles showed a marked decrease in the viscosity compared to an all coarse suspension. Contrarily, suspensions with mainly fine particles and few coarse particles showed very littie change fi om an all fine suspension. It could thus be concluded that... 

They all confirmed for dilute suspensions a linear relationship like eq. (1). Eirich also confirmed the inuependence of the si e of the spherical particles, but for the sulphur sols (Oden) the viscosity increased with decreasing size of the particles. The factor of proportionality turned out to be 2.9 in Bancelin s experiments about 4 for Oden s more dilute sulphur sols and very near 2.5 in the experiments of Eirich. It is essential to consider only dilute suspensions as already at a concentration of 2 or 3% by volume the deviation from linearity is appreciable. (See 3 a, p. 350). Eirich and Goldschmidt lx ) showed that with their relatively coarse suspensions the rate of shear must remain very low if inertia effects are not to spoil the results. 

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