Equivalent settling area

Equation (17.60) combines the formula for Stokes settling velocity, Vg, and that for the equivalent clarification area, r, also known as the comparison coefficient Q = (vs)CET). The vs term is... 

Airborne partieulate matter may eomprise liquid (aerosols, mists or fogs) or solids (dust, fumes). Refer to Figure 5.2. Some eauses of dust and aerosol formation are listed in Table 4.3. In either ease dispersion, by spraying or fragmentation, will result in a eonsiderable inerease in the surfaee area of the ehemieal. This inereases the reaetivity, e.g. to render some ehemieals pyrophorie, explosive or prone to spontaneous eombustion it also inereases the ease of entry into the body. The behaviour of an airborne partiele depends upon its size (e.g. equivalent diameter), shape and density. The effeet of partiele diameter on terminal settling veloeity is shown in Table 4.4. As a result ... 

Hall. R. S. "Current Costs of Profess Equipment". Chemical Eneineerinc. Anril 5.1982. Area equivalent is the area required by a settling tank to produce the same separation efficiency as the centrifuge. ... 

An irregular particle can be described by a number of sizes. There are three groups of definitions the equivalent sphere diameters, the equivalent circle diameters and the statistical diameters. In the first group are the diameters of a sphere which would have the same property as the particle itself (e.g. the same volume, the same settling velocity, etc.) in the second group are the diameters of a circle that would have the same property as the projected outline of the particles (e.g. projected area or perimeter). The third group of sizes are obtained when a linear dimension is measured (usually by microscopy) parallel to a fixed direction. 

The average particle-size distributions for a number of fireclays are shown in Table 14. Particles larger than 2(jl equivalent spherical radius are determined by a method based on settling under gravity, but for smaller particles a centrifugal method has to be employed. It is unfortunate that more information on the distribution below 2(jLis not available, since it is this fraction that contributes most to the specific surface area and related properties. Nevertheless, the data available does correlate to some extent with other physical properties. 

Logan and Wilkinson [116] improved the approach of Li and Ganczarczyk [117] by incorporating into the model a relationship between the aggregate projected area A, /, and the 2d aggregate fractal dimension d2f to account for surface area differences between fractals and equivalent-sized spheres. Since the settling velocity U... 

Equation (8.5) has the dimensions of area, and is equivalent to the required plan area of a settling tank operating under ideal conditions needed to perform the same clarification duty as the centrifuge (see Equation 7.4). 

There are a number of factors that will enter into situations similar to Acme s. The conditions just described are common. Instead of focusing entirely on the cost reduction benefit, an equivalent amount of time should be spent on strategic contributions. This avoids the trap described at the beginning of this chapter — having all cost reduction projects settle into the lower left-hand corner as shown in Figure 26.1. Such an analysis might also point to additional areas for financial benefits. 

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