Compressed fluid sedimentation

Fig. Schematic layout for equipment used in compressed fluid sedimentation polymer process (top) and cross-linked polymer beads produced by this process (bottom, scale bar = 10 mm).

The final consolidation of the sediment is the slowest part of the process because the displaced fluid has to flow through the small spaces between the particles. As consolidation occurs, the rate falls off because the resistance to the flow of liquid progressively increases. The porosity of the sediment is smallest at the bottom because the compressive force due to the weight of particles is greatest and because the lower portion was formed at an earlier stage in the sedimentation process. The rate of sedimentation during this period is... 

A practical explanation for the velocity-porosity variations is provided by a simple elastic theory (Wood, 1941) where seawater-saturated, unconsolidated marine sediments are considered to be nonrigid systems, consisting of discrete, noninteracting mineral grains suspended in seawater (Hamilton, 1971,1972). Sound velocity would only depend on the relative proportion of solid and fluid, and their respective compressibilities and densities, expressed through Hookean elastic equations (except for attenuation which must be treated viscoelastically) (Hamilton, 1972,1980). 

Expression. Both sedimentation and filtration are suitable separation techniques when the mixture of liquid and solids is sufficiently mobile to allow pumping, or similar method of motion, of the fluid to a barrier which retains the solid but not the liquid. If such movement is not possible then separation can be accomplished by compressing the mixture under conditions which permit the liquid to escape while retaining the solid between the compressing surfaces. This technique is called expression. Design of expression equipment is varied. Batch systems usually operate by the application of hydraulic pressure in units such as the box press, pot press, curb press and cage press. Continuous expression utilises equipment such as screw presses, roller mills, and belt presses [23]. 

Streefer, V. F., ed. 1961. Handbook of Fluid Dynamics. New York McGraw-Hill. A classic handbook on fluid dynamics wifh confributions from distinguished experts. Written for engineers and scientists in the field. Deals wifh bofh fundamenfal concepts and applications. Covers fluid flow (one-dimensional, ideal, laminar, compressible, two phase, open channel, stratified), turbulence, boundary layers, sedimentation, turbomachinery, fluid transients, and magnetohydrodynamics. Includes many formulas, equations, tables, graphs, and illustrations. Each chapter has a bibliography and the volume has subject and author indexes. 

A third system that is claimed to behave as a model hard sphere fluid is a dispersion of colloidal silica spheres sterically stabilized by stearyl chains g ted onto the surface and dispersed in cyclohexane ". Experimental studies of both the equilibrium thermodynamic and structural properties (osmotic compressibility and structure factor) as well as the dynamic properties (sedimentation, diffusion and viscosity) established that this system can indeed be described in very good approximation as a hard sphere colloidal dispersion (for a review of these experiments and their interpretation in terms of a hard sphere model see Ref. 4). De Kruif et al. 5 observed that in these lyophilic silica dispersions at volume fractions above 0.5 a transition to an ordered structure occurs. The transition from an initially glass like sediment to the iridescent (ordered) state appears only after weeks or months. 

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