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A Qualitative Fluidization Segregation Test for Pneumatic Transport

Segregation is a constant problem in industrial processes concerning bulk solids. It is generally either of a mechanical nature or a product of fluidization or pneumatic transport. The mechanical effect is called granular convection or more commonly the brazil nut effect, in which mechanical agitation of a granular medium segregates the particles, such that the largest particles end up on top. The opposite effect is observed in fluidized systems such as pneumatic conveyance systems, where the larger particles are unable to be carried into the airstream, so that segregation leaves them on the bottom of the system.

In this work we will exemplify uses of these opposing effects to quickly evaluate the propensity of a fluidized system to segregate. 

Segregation is a known issue in the pneumatic transport of milk permeate. Since the subsequent processing step—dissolving the permeate—is highly sensitive to particle size, it would be helpful to have a method for determining the propensity.

Experimental 

Samples 

The samples consist of milk permeate with a propensity for segregation (highly polydisperse) as well as a control sample consisting of 70 µm glass beads (MS 400). The glass beads have a very low polydispersity and do not segregate.

Rheometer Set Up

The measurements were carried out with an Anton Paar MCR 302 equipped with a powder cell. The measurement geometry used was a 2-blade stirrer. The powder cell is shown in Fig. 1 installed in a rheometer with the measuring glass (borosilicate glass coated with indium tin oxide).

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