Sinking velocity of particles

Various parameters of speed determine whether a mixture may separate or continue to flow. In fact, the designer of a thickener or a mixer is often more interested in the sinking velocity of particles. On the other hand, the designer of a pipeline has to pay attention to the critical velocity of flow, setding speed, and whether the flow is vertical or horizontal, particularly in the case of heterogeneous flows. 

Fig. 5.4 shows the effect of the dynamic viscosity /z upon Although the state of flow in the tank is turbulent, the viscosity of the medium is important, because it affects the sinking velocity of the particle swarm iVss. The particle Reynolds number Rep formulated with Wss and dp ties in the laminar to transition ranges. 

On the basis of the analogy between no.9 and dp (Fig. 5.5), on the one hand, and the sinking velocity of the particle swarm Wss and dp, on the other, the sinking velocity of the swarm u>gs was later incorporated into the relevance list. This consciously took account of the fact, that this property of the particle swarm is calculated from the sinking velocity Wg of a single particle in a liquid at rest and thus strictly speaking only applies to a liquid at rest. 

Since at the fluidization point the superficial velocity v and the sinking velocity of the particle in the swarm iVjs are equal to one another, v can be replaced by Wjs in the above equations. 

From what has been said above, it should be borne in mind that the sinking velocity of a single particle w, which has been mostly calculated for monodisperse... 

The study carried out by Geisler et al. [152], which considered the dimensioning of the specific stirrer power per unit mass of the suspension e = FlpV, indicated the paramount importance of the D/dp parameter. In industrially-sized tanks (D/dp > 500) this quantity consists of two sum terms from an Ejs, which is required for maintaining that vertical flow rate n>t, which is equal to the terminal sinking velocity of the particle swarm Wss, and from the term edre, which covers the frictional losses of the flow upon reversal of the flow direction ... 

REEs must depend on their partitioning between dissolved and particulate phases and a mean sinking velocity of the particles. Available data on the REEs associated with suspended particles are summarized in Table 2. 

This law is valid for solid spherical particles up to Re 1. The curve rigid spheres can be used to calculate the final rising or sinking velocity of solid spheres for Re I. 

TABLE 1-8 Sinking Velocity of Soil Particles (after Sulzer Pumps, 1998, with... 

Particle sinking rates are of considerable interest because the fester a particle can make the trip to the seafloor, the shorter the time it is subject to decomposition or dissolution and, hence, the greater its chances for burial in the sediments. The length of the trip is dictated by the depth to the seafloor, the horizontal current velocity, and the particle sinking rates. As shown in Figure 13.5, sedimentation rates decrease with increasing water depth. This relationship reflects the preservation issue and the feet that coastal waters tend to have larger sources of particles to the surfece zone. 

Figure 23.2 Removal of suspended particles (described by the solid-to-water phase ratio rsw) with uniform sinking velocity vs. (a) No mixing constant particle flux Fs = rsw vs until upper horizon reaches the bottom after time t = h /vs (b) homogeneously mixed system exponential decrease of rsw (c) change of mean particle flux across level z0 for the case of heterogeneous distribution of particles and a spatially variable vertical velocity component.

In conclusion, the first-order particle removal model, Eq. 23-16, is a reasonable approximation to describe the influence of suspended particles on sorbed chemical species. However, the sinking velocity is not necessarily identical with the Stokes law velocity, but rather is an empirical parameter which may strongly depend on lake currents and biological processes and may vary over short time periods. 

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