Granulometry / Grain Size

 

What is granulometry?

Also know as the mesh number, it is the distribution of the size of a grain, whether sand, gravel, activated carbon, anthracite, zeolite and a wide range of other granular media. The particle size is usually expressed in the U.S. Standard Sieve test with the aid of a sieve or mesh stack.

Screening is a method of separating a mixture of grains or particles into two or more size fractions, large materials are trapped above one screen, while smaller materials can pass through and be retained by other, lower screens.

Meshes or sieves can be used in the piles, to divide the grains into various size fractions and thus determine the particle size distributions. Meshes or sieves are generally used on particle sizes larger than approximately 50 microns (0.050 mm).

Each mesh or sieve is represented by a number that indicated the number of threads crossed per square inch, for example: mesh number 8, has 8 vertical threads and 8 horizontal threads, forming a grid per square inch.

The granulometries of the granular media used in water treatment are expressed in two figures, for example, an 8 x 30 mesh activated carbon or granulometry means a range of particles that pass through mesh number 8, and are retained in mesh number 30; this indicates that the granulometry or particle range is 2.38 mm to 0.595 mm.

Mesh Number Conversion Chart (U.S. Standard Sieve) to Millimeters and Inches.

Mesh Number (U.S. STD. Sieve)	Aperture (mm)	Aperture (in)
4	4.76	0.187
5	4.00	0.157
6	3.35	0.132
8	2.38	0.0937
10	2.00	0.0787
12	1.68	0.0661
14	1.41	0.0555
16	1.19	0.0469
18	1.00	0.0394
20	0.841	0.0331
25	0.707	0.0278
30	0.595	0.0234
35	0.500	0.0197
40	0.420	0.0165
45	0.354	0.0139
50	0.297	0.0117
60	0.250	0.0098
70	0.210	0.0083
80	0.177	0.0070
100	0.149	0.0059
200	0.074	0.0029
325	0.044	0.0017
400	0.037	0.0014

What is effective particle size?

The size of filter media is commonly specified in terms of effective size and coefficient of uniformity, or in terms of particle size range. Effective particle size is defined as the mesh opening through which only 10% (by weight) of a representative sample of the filter media passes.

What is the coefficient of uniformity?

It is the ratio calculated by dividing the mesh opening through which 60% (by weight) of a representative sample of a filter material passes by the mesh opening through which only 10% (by weight) of the sample passes.