Mixers for powders fall into two categories

Mixers for powders fall into two categories:

1.Diffusive (passive) mixers: in this type of mixer, homogeneity is achieved as a result of the random motion of the particles when the particle is in flow under the effect of gravity or vibration, without mechanical agitation. The mechanism is assimilated to ‘diffusion’ (Hwang and Hogg, 1980), in reference to the random movement of molecules. There is almost no shear. Consequently, these mixers are particularly suitable for particulates that require gentle mixing, such as fragile agglomerates, but they do not perform well with cohesive powders.

2.Convective (active) mixers: in this type of mixer, mixing is achieved by mechanical agitation. Parts of the bulk material are ‘conveyed’ with respect to each other by the action of impellers or turbulent gas flow. Shearing occurs and may be considerable.

In practice, most powder mixers function by a combination of both mechanisms (Harnby, 1985). In addition to mixing, powder mixers may perform other functions in powder processing technology. Some of these additional functions are:

1.Particle coating

2.Agglomeration

3.Admixture of liquids (such as fat into a dry soup mixture)

4.Drying

5.Size reduction, change of particle shape.