Power curves, study size

Yet another example of semiempirical scale-up effort was based on the fact that normalized power profiles are very similar and allow for direct comparison of different size granulators, at least for the equipment and materials used in the study. Normalized power curve rose at a relatively constant rate in the region where the ratio of water to dry mass is 0.1-0.2 ( slope plateau ). Despite a rapid increase in the slope of the power curve, the desired end-point was still detectable at a moment when the slope of the power consumption signal exceeded the plateau level by a factor of 5 (empirical observation). Using this approach, an acceptable end-point (target particle size of 135 pm) was first established on a 10-L Fielder and then scaled to 65-L Fielder and 250-L Diosna. 

Plots for power number against Reynolds number on log-log coordinates, the so-called power curves, are available in the literature for particular mixer configurations. Power curves are independent of vessel size and are particularly useful in the scale-up of liquid mixers from pilot plant studies. It must be considered, however, that a given curve is only applicable to the geometric configuration for which it was developed. 

In recent years, high-resolution x-ray diffraction has become a powerful method for studying layered strnctnres, films, interfaces, and surfaces. X-ray reflectivity involves the measurement of the angnlar dependence of the intensity of the x-ray beam reflected by planar interfaces. If there are multiple interfaces, interference between the reflected x-rays at the interfaces prodnces a series of minima and maxima, which allow determination of the thickness of the film. More detailed information about the film can be obtained by fitting the reflectivity curve to a model of the electron density profile. Usually, x-ray reflectivity scans are performed with a synchrotron light source. As with ellipsometry, x-ray reflectivity provides good vertical resolution [14,20] but poor lateral resolution, which is limited by the size of the probing beam, usually several tens of micrometers. 

Several attempts were made to evaluate the use of FBRM particle size analyzer as a potential tool for granulation end-point determination. Dilworth et al.f have compared power consumption, FBRM, and acoustic signals in a study of a wet granulation process in Fielder PMA 200 mixer. It was found that these techniques were complimentary, with FBRM probe capable to follow median granule size growth even when the power consumption curve showed a plateau. 

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