Water tools

Effective size and uniformity coefficient from a sieve analysis

Two numbers describe a filter medium: the size 10% of the grains are finer than, and how uniform the rest is. Both come straight off the sieve curve.

Sieve opening in mm and cumulative percent finer, one pair per line

Effective size (d10)

0.53mm

Uniformity coefficient (d60/d10)

1.43

d60

0.75mm

Typical media

Sand

ES 0.4 to 0.8 mm, UC 1.3 to 1.7, density 2.65, porosity 40 to 43%

Anthracite

ES 0.8 to 2.0 mm, UC 1.3 to 1.7, density 1.4 to 1.8, porosity 47 to 52%

Garnet

ES 0.2 to 0.4 mm, UC 1.3 to 1.7, density 3.6 to 4.2

Granular activated carbon

ES 0.8 to 2.0 mm, UC 1.3 to 2.4, density 1.3 to 1.7

How it works

E S = d_{10} U C = \frac{d_{60}}{d_{10}}

(1)

where

$E S$: effective size, mm
$d_{10}$: grain size that 10% of the media by mass is finer than, mm
$d_{60}$: grain size that 60% by mass is finer than, mm
$U C$: uniformity coefficient

The sieve curve is interpolated between the two bracketing sieves on a logarithmic size axis, which suits the near-lognormal distributions of processed media. A low uniformity coefficient limits stratification after backwash; fines at the top raise head loss and coarse grains at the bottom are hard to fluidise. Sieve size under-reads the equivalent sphere diameter by 5 to 10% for sand and anthracite, which the head-loss coefficients absorb.

Effective size and uniformity coefficient from a sieve analysis

How it works

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