Differential settling

It reduces ponding, which minimizes infiltration and reduces subsequent differential settling... 

In settling, particles of different gravitational settling velocities may collide (agglomeration by differential settling). 

Heterodisperse Suspensions. The rate laws given above apply to monodisperse colloids. In polydisperse systems the particle size and the distribution of particle sizes have pronounced effects on the kinetics of agglomeration (O Melia, 1978). For the various transport mechanisms (Brownian diffusion, fluid shear, and differential settling), the rates at which particles come into contact are given in Table 7.2. 

The Central Aerosol Laboratories, Columbia University, have used differential settling techniques to calibrate their more elaborate instrumentation (1W, 4W). 

Physicochemical. FREEZING OF DROPLETS. Taylor and Harmon (2Q) have sprayed drops of water into a bath of hexane cooled by dry ice. The drops are frozen and subsequently settle onto shutters, which are later opened. Differential settling theory is used to give drop sizes. Choudhury and Stevens (IQ) capture and instantaneously freeze an entire spray in a bath of liquid nitrogen, and later determine size distributions by screening techniques. 

For nonuniform suspensions it is sometimes possible to combine scattering theory with differential settling to obtain a size-distribution curve. 

Berger W.H. and Piper D.J.W. (1972) Planktonic foraminifera Differential settling, dissolution, and redeposition. Limnol. Oceanogr. 17, 275-287. 

The third collision mechanism, differential settling, occurs when larger aggregates settle more rapidly than smaller aggregates and particles (see Fig. lc). The terminal velocity of settling particles and aggregates is typically assumed to follow Stoke s law for Reynold s numbers much less than one, where the drag coefficient is approximated by... 

Marine snow determined by size-porosity and settling velocity data collected by others. The assumption was made that differential settling was the primary collision mechanism. 

Differential settling was thought to be significant in this system due to the high density of hematite (5.24 g/cm3), and the long-term nature of the... 

Domination of aggregation kinetics by differential settling implies more significant influences of hydrodynamics. Hydrodynamic corrections on the order of 10-4 were demonstrated by Han and Lawler [3], indicating a significant portion of the collision efficiency may be attributable to hydrodynamic forces. 

These trajectory methods have been used by numerous researchers to further investigate the influence of hydrodynamic forces, in combination with other colloidal forces, on collision rates and efficiencies. Han and Lawler [3] continued the work of Adler [4] by considering the role of hydrodynamics in hindering collisions between unequal-size spheres in Brownian motion and differential settling (with van der Waals attraction but without electrostatic repulsion). The results indicate the potential significance of these interactions on collision efficiencies that can be expected in experimental systems. For example, collision efficiency for Brownian motion will vary between 0.4 and 1.0, depending on particle absolute size and the size ratio of the two interacting particles. For differential... 

Three particle transport processes that bring about interparticle contacts are considered here Brownian diffusion (thermal effects), fluid shear (flow effects), and differential settling (gravity effects). Following Smoluchowski s approach, the appropriate individual transport coefficients for these three processes arc as... 

Stoll, H. M. Ziveri, P. 2002. Separation of monospecific and restricted coccolith assemblages from sediments using differential settling velocity. Marine Micropaleontology, 46, 209-221. 

SORTING CLASSIFIERS. Devices that separate particles of differing densities are known as sorting classifiers. They use one or the other of two principal separation methods—sink-and-float and differential settling. 

DiFTerential settling methods. Differential settling methods utilize the difference in terminal velocities that can exist between substances of different density. The density of the medium is less than that of either substance. The disadvantage of the method is that since the mixture of materials to be separated covers a range of particle sizes, the larger, light particles settle at the same rate as the smaller, heavy ones and a mixed fraction is obtained. 

Differential settling times are not a problem because the saturated solutions are generated and measured almost instantaneously, all within the same system. 

---