Particulate large aggregates

Large numbers of simulations have shown that the dominant effects of coagulation are the limitation that aggregations put on algal populations and the enhanced rates of export of particulate matter that result from the formation of the large aggregates (36, 37). 

Particulate and Aggregative Fluidization. When the fluid phase is liquid, the difference in the densities of fluid and solid is not very large, and the particle size is small, the bed is fluidized homogeneously with an apparent uniform bed structure as the fluid velocity exceeds the minimum fluidization velocity. The fluid passes through the interstitial spaces between the fluidizing particles without forming solids-free bubbles or voids. This state of fluidization characterizes particulate fluidization. In particulate fluidization, the bed voidage can be related to the superficial fluid velocity by the Richardson-Zaki equation. The particulate fluidization occurs when the Froude number at the minimum fluidization is less than 0.13 [9],... 

Answers to these questions have been developed slowly in comparison to rapid advances in our knowledge of air particulates based on studies completed in the late 1960 s. This is partly a result of superior sampling devices for size and chemical characterization of air particulates, and partly a result of the more heterogeneous nature of water particulates. The size spectrum of particulates in water extends from colloidal humic substances 1 nm in size, to large aggregates such as fecal pellets or marine snow with sizes up to 10" m. The distribution of shapes, densities, surface chemical properties, and chemical composition may vary widely with size. Some fractions of the size spectrum may be living, and all particulates are subject to diverse physical-chemical and biological processes that can alter size distributions, shape, or chemical composition. 

Large quantities of particles are handled on the industrial scale, and it is frequently necessary to define the system as a whole. Thus, in place of particle size, it is necessary to know the distribution of particle sizes in the mixture and to be able to define a mean size which in some way represents the behaviour of the particulate mass as a whole. Important operations relating to systems of particles include storage in hoppers, flow through orifices and pipes, and metering of flows. It is frequently necessary to reduce the size of particles, or alternatively to form them into aggregates or sinters. Sometimes it may be necessary to mix two or more solids, and there may be a requirement to separate a mixture into its components or according to the sizes of the particles. 

Prior to injection, the prepared sample should be centrifuged for 2 to 3 min in a microcentrifuge to remove any particulate material and to degas the solution. This practice is particularly important if the sample contains protein aggregates or other large particles, and when polymers are used to increase the viscosity of sample and ampholyte solution. 

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