Particle Technology

Particle size and distributions

Problems 2.9

Question 2
The following size distribution was obtained for glass spheres by microscope examination.

Size range (um): <5 5-7 7-10 10-15 15-20 20-30 30-40 40-50 >50
Number in range: 0 50 150 200 55 45 20 5 0
Relative number: 0 0.0952 0.2857 0.3810 0.1048 0.0857 0.0381 0.0095 0
Relative mass: 0 0.0039 0.0329 0.1393 0.1051 0.2507 0.3058 0.1625 0

In the size grade 5 to 7 microns, 9.52% of the distribution is present by number (of particles present), but only 0.39% by mass (compared to the total mass). This is logical, as 1 small particle is equal to 1 large particle - for the purpose of a comparison by number of particles, but 1 large particle will have a lot more mass than 1 small particle. In fact, a mass distribution is 'weighted' by the diameter cubed. Click on the label rows to see the graphs illustrating the two different distributions.

 

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