Mixers blend time

Scale-Up of Batch Mixers The prime basis of scale-up of batch mixers has been equal power per unit volume, although the most desirable practical criterion is equal blending per unit time. As size is increased, mechanical-design reqmrements may hmit the larger mixer to lower agitator speeds if so, blend times will be longer in the larger... 

Mixer performance is often related in terms of the fluid velocity during agitation, total pumping capacity (flow of the fluid in the system) generated by one impeller, and the total flow in the tank (or sometimes as blending time or a solids-suspension criterion) [25]. 

Levey, V. and Swientek, R.J., Fluidized bed mixer cuts blending time 70%, Food Processing USA, 47 (1986) 166-167. 

First ask yourself if there is any role for fluid shear stresses in determining and obtaining the desired process result. About half of the time the answer will likely be no. That is the percentage of mixing processes where fluid shear stresses either have no effect or seem to have no effect on the process result. In these cases, mixer design can be based on pumping capacity, blend time, velocities and other matters of that nature. Impeller type location and other geometric variables are major factors in these types of processes. 

Mixers. See also Agitation blend time, 290 dimensionless groups, 290 gas dispersion, 296-301 in line type, 300,301 liquids, power and speed need, 293,295 powders and pastes, 301,303,304 power number, 290-292 quality characterization, 290-292 suspension of solids, 295-299 tank desien. 287.288 Moisture c tent, critical, 237 Molecular distillation, 425-427 equipment sketches, 427 Hickman still, 427 operating conditions, rate of evaporation. 

Recommendations for Handling Blending Requirements for Fast Reactions. For handling fast reactions, if the power requirements are unreasonable to maintain equal blend time on scale-up, then one should consider two alternates (1) inject the semi-batch feed into a recycle loop in the inlet of a static mixer and (2) do the reaction in-line while pumping out the vessel through an in-line mixer. 

Because almost all materials used in the pharmaceutical industry have NIR spectra, the use of NIR for assuring blend homogeneity may prove to be a valuable application. Ciurczak [24,25] reported some of the first work on this subject. His work involved the use of a fiber probe to collect spectra from various locations in the mixer. Spectral matching and principal component analysis (PCA) were used to measure how similar the powder mix in a particular portion of the blender was to a predetermined good, or complete, mix. The match index or PCA scores were plotted versus time to assess the optimal blending time. 

In many applications the blend time is closely related to the actual number of revolutions made by the mixing device. Thus if mixing were successfully accomplished in 5 min at 60 rpm in a small mixer, the same uniformity could be achieved in fO min at 30 rpm in a larger mixer. Other factors, such as the rate of heating, could limit scale-up and mixing times. 

If blend time is excessive on a large scale without requiring impractical power input, use a circulation loop containing static mixers. 

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