PARTICLE TECHNOLOGY

Solid/solid mixing - Chapter 12

Segregation during solid mixing

This video (opens in new window) illustrates segregation (due to particle size) during a mixing process. In the video the dark coloured finer particles visibly segregate from the white coloured larger particles. This is an excellent example of the counter-intuitive nature of mixing, it could have been assumed that mixing for longer will guarantee the best mixture quality. Clearly, the video demontstrates that this is not the case and, in fact, mixing for longer causes a higher degree of particle segregation.

Segregation is a major concern during particle mixing and it is driven by any physical property of the solids that may differ between the solids to be mixed; e.g. size, density, rotational inertia, shape...

Answers to problems at the end of Chapter 12:

Problem 2
Download the Excel spreadsheet here.
The standard deviation of the randomly mixed powder is in a red coloured cell.
The spreadsheet allows you to vary the proportions, sizes, etc. to see the effect on mixing. Try changing component C to 5000 microns and see the graph change.
See Figure 12.5 for more information on mixing time and how to use sigma_R to estimate this.

Problem 3
Convert these distributions to n₃(x), then calculate the weight weighted mean particle mass, see equation (2.32), use these values and the data in the question in the above spreadsheet to determine the random between sample standard deviation. See Figure 12.3 for information on how to interpret the use of standard deviation and mixing efficiency.

FAQ

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