Floe simulation

I Goodarznia, DN Sutherland. Floe simulation Effects of particle size and shape. Chem Eng Sci 30 407-412, 1975. 

Obviously the volume of solid carbon within an aggregate is the product of the number of particles Nj, times the volume of an elementary particle (assumed to be spherical). It follows that the measured projected area (a two dimensional quantity) of an aggregate can be related to the project area of its calculated equivalent sphere (a three dimensional quantity) through a scaling law. Medalia et al. performed a so-called "floe simulation" to establish the following equality i ... 

Using his floe simulation approach, Medalia has established the following practical relationship between the so-called "void ratio," i.e., the ratio of the equivalent sphere Ves to the solid volume V, and the DBF absorption number, i.e. 

A4.2 Medalia s Floe Simulation for Carbon Black Aggregate... 

Torres, F. E., Russel, W. B., and Schowalter, W. R., Floe structure and growth kinetics for rapid shear coagulation of polystyrene colloids. J. Colloid Interface Sci. 142, 554-574 (1991a). Torres, F. E., Russel, W. B., and Schowalter, W. R., Simulations of coagulation in viscous flows. J. Colloid Interface Sci. 145, 51-73 (1991b). 

The term D is called the fractal index and represents the packing change with distance from the centre of the floe. Computer simulation and experiments allow the value of D to be related to the mechanism of aggregation. Typical values are for ... 

Laboratory Flocculant Testing. The objective of laboratory testing of flocculants is lo determine which chemical composition and molecular weight will give the best cost performance. The usual method is lo simulate on a laboratory scale the formation of floes and then subject them to the same or similar types of forces as would be encountered in a full-scale dewatering device. 

The raw material that reaches the factory is a far cry from Avicel or Solka Floe that are used by many experimenters to simulate cellulosic products (Table I). In addition to the fact that the cellulose is tied up in a lignin-hemicellulose-cellulose (LHC) complex, it should be recognized that the terms lignin and hemicellulose are catchall terms covering a range of compositions and molecular weights. 

Similar methods were employed by Schonberg et al. (1986) to investigate the multiparticle motions of a finite collection of neutrally buoyant spheres suspended in a Poiseuille flow. They were also used by Ansell and Dickinson (1986) to simulate the fragmentation of a large colloidal floe in a simple shear flow. 

Testing for applications in belt presses is most commonly done by flocculation in beakers and visual observation of the size and strength of the formed floes. The conditioned sluny can be poured into a filter for a gravity drainage test. These tests can be useful for an e3q>erienced person to evaluate if a sluny can be used in belt presses and to optimize an existing belt press. However, the simulation of the final cake dryness is not... 

Hsu, j. R Tsao, H. K. 1992 Dynamic simulation of floe breakage with a random breakage distribution. Colloids and Surfaces 62, 23-30. 

Circles in the figure simulate the sludge floes, the diameters of which are takoi as 700 and 200 microns for the ordinary and bulking sludges,... 

Figure 4.15 Transmission electron micrographs of hematite in the presence of schizophyllan under conditions of rapid kinetics. Schizophyllan/hematite ratio 3.79, pH 4.5, /= 1 mmol dm". The three-dimensional floe obtained by computer simulation (optimum conditions) explains the presence of a local linear order observed in the hematite Hoc due to the presence of rigid...

Both experiments and computer simulations demonstrated the fractal character of the mixed floes. The optimal schizophyllan biopolymer/hematite concentration ratio obtained by simulation was smaller than that observed in laboratory experiments. The shift in the optimal dose was mainly attributed to a higher than predicted affinity of hematite for the schizophyllan aggregates present in the initial solution in addition to the presence of a large proportion of chains that did not participate in the flocculation process [12]. 

Physical properties, such as floe densities, settling velocities or the diffusion of compounds inside aggregates and floes, depend on their fractal dimensions, which have to be calculated. The floe fractal dimensions can be determined directly from simulation, since each monomer and particle position is repeatedly computed during a simulation, allowing the mathematical definition of a fractal to be applied directly. 

For aggregates or floes which may arise on Brownian coagulation of solid ufp, a number of simulation techniques have been proposed [2.71-78]. These techniques... 

With biological floes, reaction rates should be plotted as illustrated in Fig. 5.70 (Atkinson, 1974). With increasing film thickness, and with larger particles, the curve moves to higher S values. Again, dotted lines represent the computer simulation, while solid lines correspond to experimental situations. 

Sutherland D (1966) Comment on Void s simulation of floe formation. J Colloid Interface Sci 22 300... 

Medalia, A.I. (1967) Morphology of aggregates I. Calculation of shape and buMness factors application to computer-simulated floes, J. Colloid Interface Sci., 24, 393. 

Structures of some flocculated colloidal systems are observed to have a fractal character similar to that generated in computer simulation models. " The number of particles within a floe of radius rf is given by... 

Dickinson, E. and S.R. Euston. 1992. Short-range structure of simulated floes of particles with bridging polymer. Colloids and Surfaces 62 (3) 231-242. 

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