Segregation granular mixing

Shinbrot, T. Muzzio, F.J. Non-equilibrium patterns in granular mixing and segregation. Physics Today, March, 2000 25-30. 

Wightman, C. Muzzio, F.J. Mixing of granular material in a drum mixer undergoing rotational and rocking motions I. Segregating particles. Powder Tech. 1998, 98, 125-134. 

Ottino J, Khakhar D. Mixing and segregation of granular materials. Annu Rev Fluid Mech... 

Although the molecules of a single-phase liquid system may differ, and may diffuse at different rates, they will ultimately achieve a random distribution within the confines of the system. Particulate and granular components do not usually have the constant properties of molecular species and can differ widely in physical characteristics. Thus a mixing motion which depends on identical particulate properties is unlikely to achieve its objective. More commonly such a mixer would produce a grading or segregation of... 

The feed hopper feeds the granular material to the extruder. In most cases, the material will flow by gravity, unaided, from the feed hopper into the extruder. Unfortunately, this is not possible with all materials. Some bulk materials have very poor flow characteristics and additional devices may be required to ensure steady flow into the extruder. Sometimes this can be a vibrating pad attached to the hopper to dislodge any bridges as soon as they form. In some cases, stirrers are used in the feed hopper to mix the material (and prevent segregation) and/or to wipe material from the hopper wall, if the bulk material tends to stick to the wall. 

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