Suspending fluid

A PVDF membrane filter has been shown to remove >10 particles of vims for vimses >50 nm independent of fluid type (8). Vimses smaller than 50 nm are not removed as efficientiy but are removed in a predictable manner which correlates to the vims particle size. The chemistry of the suspending fluid affects titer reduction for vimses <50 nm owing to other removal mechanisms, such as adsorption, coming into play. The effects of these other mechanisms can be minimized by using filtration conditions that minimize adsorption. 

Mobility is affected by the dielectric constant and viscosity of the suspending fluid, as indicated in Eq. (22-28). The ionic strength of the fluid has a strong effect on the thickness of the double layer and hence on As a rule, mobility varies inversely as the square root of ionic strength [Overbeek, Adv. Colloid Sci., 3, 97 (1950)b... 

Sednientation of particles in a suspending fluid 10 3 to 10 6 Spices in salad dressing... 

As the gas flow is increased beyond the behavior of the bed depends on the density difference between the particles and the suspending fluid. If the... 

Cell response to hydrodynamic stress has frequently been evaluated in terms of the release of intracellular components into the suspending fluid. An increase in... 

Potential chemical preservatives may be evaluated in the first place by the methods outlined above, especially by determining MIC values (section 3.6) or by viable counts (section 3.2). TheRW, CM andKS tests (sections 3.1.1 and 3.1.2) have no relevance in preservative evaluation. It will be recalled (section 2.5) that formula ingredients may reduce the efficiency of a preservative which has shown up well in conventional tests using culture media as the suspending fluid. 

Fig. 15. Affine stretching of a filament in the journal bearing flow. Experiments (top) agree well with computations (bottom) carried out assuming that the filament deforms as the suspending fluid (i.e., affine deformation) (Tjahjadi and Ottino, 1991).

Independent bacterial motion is a true movement of translation and must be distinguished from the quivering or back-and-forth motion exhibited by very small particles suspended in a liquid. This latter type of motion is called Brownian movement and is caused by the bombardment of the bacteria by the molecules of the suspending fluid. 

The velocity gradients in the suspending fluid flowing upward between the particles are increased, resulting in greater shear forces. 

There are essentially three different approaches to describing hindered settling. One approach is to define a correction factor to the Stokes free settling velocity in an infinite Newtonian fluid (which we will designate F0), as a function of the solids loading. A second approach is to consider the suspending fluid properties (e.g. viscosity and density) to be modified by the... 

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... 

Barnea and Mizrahi (1973) considered the effects of the modified density and viscosity of the suspending fluid, as represented by Eq. (14-21), as well as a crowding or hindrance effect that decreases the effective space around the particles and increases the drag. This additional crowding factor is 1 + k2(pl/3, which, when included in Eq. (14-21), gives... 

This result can also be applied directly to coarse particle swarms. For fine particle systems, the suspending fluid properties are assumed to be modified by the fines in suspension, which necessitates modifying the fluid properties in the definitions of the Reynolds and Archimedes numbers accordingly. Furthermore, because the particle drag is a direct function of the local relative velocity between the fluid and the solid (the interstitial relative velocity, Fr), it is this velocity that must be used in the drag equations (e.g., the modified Dallavalle equation). Since Vr = Vs/(1 — Reynolds number and drag coefficient for the suspension (e.g., the particle swarm ) are (after Barnea and Mizrahi, 1973) ... 

The poor response of the synthetic polymers in the cytotoxicity tests with insulinoma cells (Table 4) provides further support for the utilization of polyanions as the inner cell suspending fluids. Given the rigid nature of the moderate molecular weight anionic polysaccharides, it seems reasonable that low molecular weight polycations can be effective in membrane formation, due to their high diffusivity. This will be elaborated upon in the discussion. 

Slurry reactors are similar to fluidized-bed reactors in that a gas is passed through a reactor containing solid catalyst particles suspended in a fluid. In slurries, the catalyst is suspended in a liquid, whereas in fluidized beds, the suspending fluid is the reacting gas itself. 

Moreover, the influence of the motions of the particles on each other (i.e., when the motion of a particle affects those of the others because of communication of stress through the suspending fluid) can also influence the measured diffusion coefficients. Such effects are called hydrodynamic interactions and must be accounted for in dispersions deviating from the dilute limit. Corrections need to be applied to the above expressions for D and Dm when particles interact hydrodynamically. These are beyond the scope of this book, but are discussed in Pecora (1985), Schmitz (1990), and Brown (1993). 

S. J. Johnson, P. L. Frattini and G. G. Fuller, Simultaneous dichroism and birefringence measurements of dilute colloidal suspensions in transient shear flow, J. Colloid Interface Sci., 104,440 (1985) S. J. Johnson and G. G. Fuller, Flowing colloidal suspensions in non-Newtonian suspending fluids decoupling the composite birefringence, Rheol. Acta, 25, 405 (1986). 

Microfiltration (MF) and ultrafiltration (UF) involve contacting the upstream face ofa porous membrane with a feed stream containing particles or macromolecules (B) suspended in a low molecular weight fluid (A). The pores are simply larger in MF membranes than for UF membranes. In either case, a transmembrane pressure difference motivates the suspending fluid (usually water) to pass through physically observable permanent pores in the membrane. The fluid flow drags suspended particles and macrosolutes to the surface of the membrane where they are rejected due to their excessive size relative to the membrane pores. This simple process... 

Conversion of fiberboard furnish to board begins with the felting operation. Fibers suspended in a liquid or gaseous fluid are deposited on a moving wire and concentrated into an interfelted mat by the removal of the suspending fluid. Application of pressure between rolls or platens in the cold-press operation further reduces interfiber void space and expresses the forming fluid. 

When the particle is moving relative to the suspending fluid, transport of heat or matter is enhanced by convective diffusional processes. Under conditions where the particle exists in a rarified medium (Kn 0), the heat and mass tranfer relations are modified to account for surface accommodation or sticking of colliding molecules and the slippage of gas around the particle. 

Gravimetric Properties—The important equations pertaining to suspensions have been developed in Chapter 4 in conjunction with the determination of particle-size. The density of the suspension is readily apparent in the characteristic suspension equation developed there, but will be repeated for the sake of completeness. Let W be the total weight of the particles and p their density if the volume of the suspension is designated as V, and if the suspending fluid is water, then the specific gravity [Pg.344]

Van der Waals interactions between identical solid particles are always attractive [7]. However, if the Hamaker constant of the suspending fluid is intermediate between the Hamaker constants of two different particles, the van der Waals interactions will be repulsive [9]. Moreover, in view of the finite speed of propagation of electromagnetic radiation, the response of a molecule to perturbations in the electric field deriving from another nearby molecule is not instantaneous. Retardation effects are observable at separation distances as small as 1 or 2 nm, and they become prominent at larger distances (>10 nm) [50]. Gregory [50] has proposed a simple expression for describing retarded van der Waals interactions between flat plates ... 

The methods of measuring the velocity of electrokinetic motion are fully described in some of the reviews mentioned above. They include (for cataphoresis) various forms of U-tube in which the motion of the boundary of the suspension is observed, transference methods similar to Hittorf s transport number measurements in electrochemistry, and microscopic cells in which the motion of individual particles is watched, due allowance being made for the motion of the suspending fluid in the opposite direction to the particles. Sumner and Henry s device1 of fixing a sphere on a fibre and observing its deflexion in a horizontal electric field is very ingenious, and not so frequently mentioned as other methods. 

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