Most of available scale-up rules for dry powder mixing/ blending operation are applicable for geometrically similar equipments. Considering, equipments unavailability, sometime a blender with geometrically not similar is proposed for scale up batches. In such situation, how to determine different process parameters associated with blending unit operation?
Dear Srimanta,
The first non-Geometric Scale up is with Geometric Similarity from the bench scale mixing results to the plant scale tank diameter this scale up step will not account for the actual production tank volume, number of impeller or impellers size.one or more mixing characteristics, such as tip speed, can be duplicated by the appropriate selection of a large-scale mixer speed. The two most popular and effective geometric scale-up methods are equal tip speed and equal power per volume. Equal tip speed results when the small-scale mixer speed is multiplied by the inverse geometric ratio of the impeller diameters to get the large-scale mixer speed:
N2 = N1(D1/D2)
Equal power per volume involves a similar calculation, except the geometry ratio is raised to the two-thirds power:
N2 = N1(D1/D2)(2/3)
This expression for power per volume only applies strictly for turbulent conditions, where the power number is constant, but is approximately correct for transition-flow mixing.
Five steps
the recommended approach for doing non-geometric scale-up is as follows:
1. Calculate the laboratory- or pilot-plant-scale values for the mixing variables listed in the sidebar.
2. Do a geometric-similarity scale-up to the large-scale tank diameter. Use a criterion such as tip speed to set the large-scale speed. Calculate the mixing variables for the new, large-scale conditions.
3. As needed, change the impeller diameter at the large scale. Calculate the mixing variables and, if required, modify speed to keep an important variable such as tip speed or torque per volume constant.
4. Switch impeller type, if desired or necessary, and recalculate mixing variables using the appropriate power number for the new impeller. Calculate the mixing variables and make decisions or adjustments as required.
5. Alter the liquid level, if necessary, to match volume specifications at the large scale. Calculate the mixing variables again for the new liquid level. If undesirable changes occur, adjust mixer speed or number of impellers.
Regards,
Prem Baboo
Hello Prem Bamboo, it is an example for non-geometric scale up for liquid, if I have a tumble blender how can I do it?
Regards!
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