Settling velocity figure

Gravity sedimentation and vacuum filtration tests were conducted on the unconditioned effluent from Run 7. The effluent exhibited rapid settling velocities (Figure 4) and the filtration characteristics were excellent (Table X). 

Figure 3.1a shows a flash drum used to separate by gravity a vapor-liquid mixture. The velocity of the vapor through the flash drum must be less than the settling velocity of the liquid drops. Figure 3.11) shows a simple gravity settler for removing a... 

Small solid particles, present in dust and grit emissions, have very low settling velocities (Table 4.4) The collection efficiencies of simple cyclones are tlierefore, as shown in Figure 17.3, relatively low. Fabric filters, electrostatic precipitators or wet scrubbers may be required to remove particles <5 pm in size with an acceptable efficiency. Therefore the cost of pollution control inevitably increases when dealing with particle size distributions skewed towards the lower end. 

Determine the settling velocity of spherical quartz particles in water (d = 0.9 mm) using the dimensionless plot of the Lyachshenko and Reynolds numbers versus the Archimedes number in the figure above. The Lyashenko number is the same as the dimensionless settling number. The specific weight of the quartz is 2650 kg/m and the temperature of the water is 20° C. 

Note that the absolute value of Pp - p has been assumed. The negative value of this difference indicates that the droplet displacement is centripetal. The value of the Reynolds number corresponding to Ar = 3650 from Figure 10 is 45. Hence we can determine the radial settling velocity from the definition of the Reynolds number ... 

Figure 4-9 is convenient for quick checks of terminal settling velocities of solid particles in air and in water [23]. 

Figure 4-8. Terminal settling velocity of particles in water. By permission, Lapple, C. E., Fluid and Particle Mechanics, 1st Ed., University of Delaware, Newark, 1954.

V = Settling velocity for hindered uniform spherical particle, ft/s or m/s Wi= Width of rectangular cone inlet duct, ft Z], = Heavy phase outlet dimensions of decanter measured from horizontal bottom, shotvn on Figure 4-12... 

A cyclone separator is an economical device for removing particulate solids from a fluid system. The induced centrifugal force (see Figure 7-6) is tangentially imparted on the wall of the cyclone cylinder. This force, with the density difference between the fluid and solid, increases the relative settling velocity. 

Airborne particulate matter may comprise liquid (aerosols, mists or fogs) or solids (dust, fumes). Refer to Figure 5.2. Some causes of dust and aerosol formation are listed in Table 4.3. In either case dispersion, by spraying or fragmentation, will result in a considerable increase in the surface area of the chemical. This increases the reactivity, e.g. to render some chemicals pyrophoric, explosive or prone to spontaneous combustion it also increases the ease of entry into the body. The behaviour of an airborne particle depends upon its size (e.g. equivalent diameter), shape and density. The effect of particle diameter on terminal settling velocity is shown in Table 4.4. As a result ... 

Equation 10.7 is used to calculate the settling velocity with an assumed droplet size of 150 pm, which is well below the droplet sizes normally found in decanter feeds. If the calculated settling velocity is greater than 4 x 10-3 m/s, then a figure of 4 x 10 3 m/s is used. 

Figure 11. Effect of biofilm growth on terminal settling velocity.

The elutriation method is really a reverse sedimentation process in which the particles are dispersed in an upward flowing stream of fluid. All particles with terminal falling velocities less than the upward velocity of the fluid will be carried away. A complete size analysis can be obtained by using successively higher fluid velocities. Figure 1.4 shows the standard elutriator (BS 893)(6i for particles with settling velocities between 7 and 70 mm/s. 

Thus, for the bulk of particles, the flow will be within region (a) in Figure 3.4 and the settling velocity is given by Stokes equation ... 

For treatment of terminal settling velocities, it is more convenient to work in terms of defined in Eq. (5-15). Figure 9.5 shows the terminal Reynolds number and (Xy - 1) as functions of For > 10, Xy is approximated closely by with Xp given by Eq. (9-17). 

FIGURE 9.15 Cunningham correction factors to be applied in calculating terminal settling velocities of particles (adapted from Hinds, 1982). 

FIGURE 9.16 Settling velocities in still air at 0°C and 760 Torr pressure for particles having a density of 1 g cm 3 as a function of particle diameter. For spherical particles of unit density suspended in air near sea level, the Stokes law applies over a considerable range of particle sizes, where the line is straight, but a correction is required at the particle size extremes (adapted from LBL, f979). 

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