Tumbler mixer

For most rapid mixing, in addition to diffusive (fine-scale) mixing, there should be a means by which large groups of particles are intermixed. This can be accomphshed by either the convective or the shear mechanism. A ribbon mixer illustrates the former, whereas a plain tumbler gives the latter. 

Table 19-2 includes impacl velocities for some internal rotating devices in tumblers as well as other mixers. Contamination and wear problems of internal rotating devices are discussed under Performance Characteristics. ... 

Trommel,/, drum barrel, cylinder tumbler (Anat.) tympanum, -darre, /. drum kiln, -fell, n., -haut, /. drumhead (Anat.) tympanic membrane, -filter, n. drum filter or strainer. -malzerei, /. drum malting, -mischer, m. drum mixer, -miihle, /. drum mill, (Ceram.) Aising cylinder. 

Although convection is typically orders of magnitude more rapid than dispersion, as a practical matter the relative contribution of each mechanism to blending is strongly influenced by the initial distribution of species in the mixer. Thus ingredients loaded in horizontal layers (Fig. 7) can be mixed relatively rapidly, while ingredients layered side by side (either intentionally (Fig. 8) or inadvertently (as a result of careless loading of a tumbler) will typically mix enormously more slowly. 

Free-fall tumbler mixer Subsampler A ladle in the lid of the mixer collects a good representative sample Large/small Can be used with fines present Representative sample produced in a short time period ... 

Diffusive mixing predominates in tumbler mixers. The material is tumbled as it is lifted past its angle of repose. Mixing occurs when a particle changes its path of circulation through a collision or by being trapped in voids presented by another layer of particles. 

Apart from the impact and vibration tests dealt with previously, there are several other tests of friability, some of which appear in British Standards dealing with specific materials. Such tests include mixer tests, jet impingement tests, shear tests, tumbler tests and fluidized bed tests. Of these, the shear tests and tumbler tests are only considered worth mentioning here, with more details available from another BMHB publication54. 

Tumbler mixers (a) double ione mixer (6) twin-shell blender. 

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