Principle of particle size testing by sedimentation method—Stokes’ law（1）

The sedimentation method is a method that reflects the particle size distribution of powder by measuring the sedimentation velocity of particles in a liquid. We know that large particles settle quickly in liquids, while small particles settle slowly. The quantitative relationship between sedimentation velocity and particle size can be obtained from the mathematical expression of Stokes' law below:

                                                                                           V=(ρ_{s -}ρ_f)g D² /18ȵ

It can be seen from the above formula that the sedimentation speed of particles is proportional to the square of the particle diameter. It can be seen that the larger the particles are, the faster the sedimentation speed is in gravity sedimentation. For example, under the same conditions, the ratio of the two particle diameters is 10:1, then this The ratio of the sedimentation of the two particles is 100:1. In this way, by measuring the sedimentation velocity of the particle, its particle size can be obtained.

In order to increase the settling speed of fine particles, shorten the test time and improve the test accuracy, many sedimentation instruments introduce centrifugal sedimentation means to speed up the settling speed of fine particles. The relationship between particle size and sedimentation velocity under centrifugation is as follows;

                                                                                         V_e =(ρ_{s -}ρ_f)ω²rD² /18ȵ