1. Size, shape, size distribution

Particle size is undoubtedly the most sought-after parameter of a powder, both for predicting its behavior and for calculating the operations that involve it: storage, flow, separation, fluidization, heat exchange, chemical reactions, dispersion, dissolution, etc. And yet what does particle size mean? And yet, what does the size of a powder mean? For a spherical particle, one and only one quantity, namely its diameter, can represent its size. All other geometric characteristics (surface area, volume, specific surface area, etc.) can be rigorously determined from this. However, the definition of a characteristic particle size becomes more complicated as (figure ):