## Particle size |

Granulometry | |
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Basic concepts | |

Particle size · · | |

Methods and techniques | |

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Related concepts | |

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**Particle size** is a notion introduced for comparing *flecks*), *droplets*), or *bubbles*). The notion of particle size applies to

- measuring particle size
- international conventions
- see also
- references

There are several methods for measuring particle size and

In all methods the size is an indirect measure, obtained by a model that transforms, in abstract way, the real particle shape into a simple and standardized shape, like a sphere (the most usual) or a *size* parameter (ex. diameter of sphere) makes sense. Exception is the

Definition of the particle size for an ensemble (collection) of particles presents another problem. Real systems are practically always

The particle size of a *particle size* cannot be applied to non-spherical particles. There are several ways of extending the above quantitative definition to apply to non-spherical particles. Existing definitions are based on replacing a given particle with an imaginary

- Volume-based particle size
- Volume-based particle size equals the diameter of the sphere that has the same volume as a given particle. Typically used in
sieve analysis , as shape hypothesis (sieve's mesh size as the sphere diameter).

- where
- : diameter of representative sphere
- : volume of particle

- Area-based particle size
- Area-based particle size equals the diameter of the sphere that has the same
surface area as a given particle. Typically used inoptical granulometry techniques.

- where
- : diameter of representative sphere
- : surface area of particle

In some measures the size (a

- Weight-based (spheroidal) particle size
- Weight-based particle size equals the diameter of the sphere that has the same weight as a given particle. Useful as hypothesis in
centrifugation anddecantation , or when the number of particles can be estimated (to obtain average particle's weight as sample weight divided by the number of particles in the sample). This formula is only valid when all particles have the same density.

- where
- : diameter of representative sphere
- : weight of particle
- : density of particle
- : gravitational constant

- Aerodynamic particle size
Hydrodynamic oraerodynamic particle size equals the diameter of the sphere that has the samedrag coefficient as a given particle.- Another complexity in defining
*particle size*in a fluid medium appears for particles with sizes below amicrometre . When a particle becomes that small, the thickness of theinterface layer becomes comparable with the particle size. As a result, the position of the particle surface becomes uncertain. There is a convention for placing this imaginary surface at a certain position suggested by Gibbs and presented in many books oninterface and colloid science .^{[1]}^{[2]}^{[3]}^{[4]}^{[5]}^{[6]}