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Porous floes

Eor vacuum filters, both the rate of filtration and the dryness of the cake may be important. The filter cake can be modeled as a porous soHd, and the best flocculants are the ones that can keep the pores open. The large, low density floes produced by high molecular weight polymers often coUapse and cause blinding of the filter. Low molecular weight synthetic polymers and natural products that give small but rigid floes are often found to be the best. [Pg.35]

For cells that are embedded in macroscopic gel-like structures such as floes, biofilms or other porous media such as soil or sediment aggregates, mass transport to the cells can decrease due to ... [Pg.462]

A reactor constructed of stainless steel 410 was used for pyrolysis since it contained no nickel. The coke layer formed during pyrolysis was usually thin and greyish. Less frequently, a piece of black coke was found on the surface. The metal surface (Surface C) was always grey. Figure 5 shows the two types of coke formed at Surface A in the stainless steel 410 reactor. The black (less frequent) coke appeared to be a floe of fine filaments, about 0.05 / m in diameter, with occasional 0.4- m filaments. The predominant deposit seems to be platelets of coke that include metal crystallite inclusions, the lighter area. The metal particles in the coke deposits, as detected by EDAX, were chromium rich compared with the bulk metal, as reported in Table III. Some sulfur also was present in the deposit the sulfur was present, no doubt, because of the prior treatment of the surface with hydrogen sulfide. Surfaces B and C for the stainless steel 410 reactor are also shown in Figure 6. Surface B indicated porous coke platelets. Surface C was covered mostly with coke platelets, and cavities existed on the surface. Metal crystallites rich in iron apparently were pulled from the metal surface and were now rather firmly bound to Surface B. Surface C was richer in chromium than the bulk metal. [Pg.222]

It has been claimed that particle shape, roughness and the nature of the material has little effect on the analysis [30] but there is considerable evidence that the size measured is the envelope of the particle. Comparison with other techniques gives good agreement for homogeneous spherical particles for non-spherical particles results may differ [31,32]. For porous particles the measured volume may be several times the skeletal volume, and the apparent volume for floes is greater than the volume of the particles that make up the floes [20]. [Pg.455]

Fig. 28 shows the mechanically deliquoring of flocculated, fragile, and high porosity cakes by belt press filter. In the process, large floes settle out rapidly on the porous belt, and the liquid flows through quickly. Sedimentation and filtration are accomplished quickly, but at a cost of producing a very soupy cake. [Pg.2785]

In summar), coagulation increases rejection for the 100 kDa membrane. Flux and rejection now approach that of the 10 kDa membrane. The rejection of the 10 kDa membrane was slightly increased in some cases. At 25 mgL" FeCft flux decUne was lower than in the absence of colloids and FeCb. This demonstrates that FeCb pretreatment can, under certain circumstances, prevent flux decline. This can be attributed to the binding of organic calcium complexes, which otherwise could penetrate into pores and lead to the deposition of a more porous cake, which is determined by the floe structure. [Pg.211]

It should be mentioned that, since the 1990s, Gmachowski (1990, 1995, 1998, 2005) has presented a series of papers which combined functional relationships derived from porous-sphere-models with experimental data. He deduced relations for the fractal prefactor kc and the hydrodynamic diameter R, which are frequently cited in the hterature (e.g. Vanni 2000 Tang et al. 2002 Gmy and Cugniet 2004 Lee and Kramer 2004). However, his experiments mainly concern coarse flocculated polystyrene latices (floe size > 100 pm), which are probably not comparable with the aggregate types discussed here (e.g. in Gmachowski s papers the fractal prefactors increase monotonically with fractal dimension, which is in striking contrast to the behaviour found in Fig. 4.8). [Pg.164]

Calculation of the terminal velocity of a porous sphere is useful and important in applications in water treatment where settling velocities of a floe or an aggregate are estimated. It is also important in estimation of terminal velocities of clusters in fluidized bed applications. The terminal velocity of a porous sphere can be quite different from that of an impermeable sphere. Theoretical studies of settling velocity of porous spheres were conducted by Sutherland and Tan (1970), Ooms et al. (1970), Neale et al. (1973), Epstein and Neale (1974), and Matsumoto and Suganuma (1977). The terminal velocity of porous spheres was also experimentally measured by Masliyah and Polikar (1980). In the limiting case of a very low Reynolds number, Neale et al. (1973) arrived at the following equation for the ratio of the resistance experienced by a porous (or permeable) sphere to an equivalent impermeable sphere. An equivalent impermeable sphere is defined to be a sphere having the same diameter and bulk density of the permeable sphere. [Pg.31]

The Coulter principle has been applied to floes but is severely constrained by the very severe shear stress that occurs within the vortex of fluid passing through a Coulter orifice. Indeed the Coulter Counter has been used as an on-line method for studying the disruption of floes. If a floe were entirely disrupted just before or in the orifice it is reasonable to assume that the additive volume of the fragments would be detected as one coincident group of particles. This would however assume that the fragments were of the same particle volume concentration as the parent, an unsafe assumption for floes. However breakup in an orifice is not normally complete and the observed size may also depend on the amount of distortion the floe experiences in the orifice. From the behaviour of other types of porous particle in die Coulter Counter it is often assumed that the instrument measures the external envelope volume if the floes are not disrupted. Attempts have been made to measure individual well characterised floes under realistic orifice conditions but the experiments are very difficult to do and the results remain ambiguous. ... [Pg.247]

De Gennes has studied the capillary condensation for the two strictly seifsimilar porous fractals iterative pits and iterative floes shown in Fig. 2 A,B. [Pg.151]

It has also been reported that aggregates produced under sweep floe conditions were more compressible than for charge neutralization conditions, resulting in compaction when the membrane filtration system was pressurized (Antelmi et al., 2001 Cabane et al., 2002). Lee et al. (2000) also reported that the specific resistance was lower with charge neutralization than with sweep floe, attributed to the formation of a less compressible and more porous cake. Judd and HUlis (2001) suggested that floes need to reach a certain... [Pg.143]


See other pages where Porous floes is mentioned: [Pg.134]    [Pg.149]    [Pg.1647]    [Pg.34]    [Pg.3]    [Pg.198]    [Pg.286]    [Pg.134]    [Pg.149]    [Pg.1647]    [Pg.34]    [Pg.3]    [Pg.198]    [Pg.286]    [Pg.82]    [Pg.523]    [Pg.323]    [Pg.112]    [Pg.163]    [Pg.455]    [Pg.331]    [Pg.353]    [Pg.594]    [Pg.1647]    [Pg.82]    [Pg.232]    [Pg.1021]    [Pg.3092]    [Pg.5111]    [Pg.375]    [Pg.749]    [Pg.22]    [Pg.261]    [Pg.337]    [Pg.55]   
See also in sourсe #XX -- [ Pg.149 ]




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