Sieve diameter

Species separated by molecular sieving effects when kinetic diameters fall iato different zeoHte aperture size categories (standard molecular sieve diameters = 300, 400, 500, 800, 1000,1300 pm. 

The particle mass retained by each sieve is determined by weighing after drying when necessary, and each fraction is designated by the sieve size it passed and the size on which it was retained. The sieve diameter of a particle is therefore defined as the size of the sieve aperture through which the particle in question just passes through. Mass fractions of the particles are then presented in tabular or graphical form. 

Dsi is the sieving diameter, equal to the width of the minimum aperture through which the particle will pass. 

However, in the typical case of an irregular-shaped particle, it is not easy to calculate its volume and thus dsph is taken equal to the mean nominal diameter measured by sieve analysis dp. In the present book, dp is considered to be equal to the average sieve diameter. 

A sieve diameter is defined as the width of the minimum square aperture through which the particle will pass. A common sizing device associated with this definition is a series of sieves with square woven meshes. Two sieve standards, i.e., Tyler Standard and American... 

Figure 1.2. Schematic illustration of multidimensions of a particle and its equivalent volume diameter, surface diameter, and sieve diameter.

Example 5.4 Determine the terminal settling velocity of a worn sand particle having a measured sieve diameter of 0.6 mm and specific gravity of 2.65. Assume the settling is type 1 and the temperature of the water is 22°C. 

The equations treated above all refer to the diameter of spherical particles yet in practice, not all particles are spherical. To use the above equations for these situations, the sieve diameter must be converted to its equivalent spherical diameter. In Chapter 5, the relationship was given as rf = 6ln) dp, where is the shape factor and dp is the sieve diameter. 

Note, again, that 4 is for a spherical particle. Eor nonspherical particles, the sieve diameter dp must be converted into its equivalent spherical particle by the equation mentioned in a previous paragraph. 

Exponent in head loss equation for deposited materials Concentration of solids introduced into bed Diameter of spherical particle Sieve diameter... 

The sieve diameter, for square mesh sieves, is the length of the minimum square aperture through which the particles can pass, though this definition needs modification for sieves which do not have square apertures. 

In many industries, particle size measurements have been carried out historically by sieve analysis and light scattering instruments are increasingly replacing this. In order to correlate with historic data banks some manufacturers have software to manipulate the data so as to present the size distribution in terms of sieve diameter. 

Molecule Molecular weight Mean free path (nm) Kinetic sieving diameter (nm)... 

Another useful equivalent diameter is the equivalent sieve diameter, it is the diameter of the largest sphere which can pass through a given sieve aperture. It should be noted that the equivalent diameter of a particle always has dimension of length. 

Since the reported diameter is an equivalent volume diameter, proper consideration must be taken when comparing the results with other particle size analysis methods. For instance, the equivalent volume diameter reported for any non-spherical shaped particle will generally be higher than the particle size reported by sieve analysis, as the equivalent volume diameter is based on the volume of a perfect sphere. This theory becomes apparent if one compares the equivalent volume diameter with the sieve diameter of a square that has dimensions of 2(X)pm by 200 pm by 200 pm and that passes through a U.S. ASTM sieve 70 (212 pm) and is retained on a U.S, ASTM sieve 80 (180 pm). In this case, the sieve diameter reported will be 212 pm but the... 

Sieve Diameter The width of the minimum square aperture through which the panicle will pa.ss... 

Equivalent sieve diameter The diameter of spherical particles that just pass through the apertures of a particular sieve. Also termed near-mesh diameter... 

Other techniques of deducing shape (or size) include using sieve analysis or sedimentation. The equivalent diameter for a sieve analysis is the mesh size of the upper sieve through which particles pass. (A more precise definition of the sieve diameter is the mean between the mesh size through which the particles pass and on which the particles are retained.) The characteristic diameter of a sedimentation technique would be the diameter of a sphere that has the same settling velocity. 

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