Scale of agitation

Figure 7-15 shows plots of Pumping number Nq and Power number Np as functions of Reynolds number Np for a pitched-blade turbine and high-efficiency impeller. Hicks et al. [8] further introduced the scale of agitation, S, as a measure for determining agitation intensity in pitched-blade impellers. The scale of agitation is based on a characteristic velocity, v, defined by... 

The basic principles employed in the preparation of parenteral products do not vary from those widely used in other sterile and non-sterile liquid preparations. However, it is imperative that all calculations are made in an accurate and most precise manner. Therefore, an issue of a parenteral solution scale-up essentially becomes a liquid scale-up task, which requires a high degree of accuracy. A practical yet scientifically sound means of performing this scale-up analysis of liquid parenteral systems is presented below. The approach is based on the scale of agitation method. For singlephase liquid systems, the primary scale-up criterion is equal liquid motion when comparing pilot-size batches to a larger production-size batches. 

The basis of the scale-of-agitation approach is a geometric scale-up with the power law exponent, = 1 (Table 1). This provides for equal fluid velocities in both large- and small-scale equipment. Furthermore, several dimensionless groups are used to relate the fluid properties to the physical properties of the equipment being considered. In particular, bulk-fluid velocity comparisons are made around the largest blade in the system. This method is best suited for turbulent flow agitation in which tanks are assumed to be vertical cylinders. 

Scale of agitation Bulk fluid velocity (cm/sec) Description of mixing... 

To illustrate the actual application of the scale-of-agitation approach to scale-up, the above method was applied to the scale-up of typical injectables solution from 378-L pilot batch to a 3780-L production-size batch. The example product is a Newtonian fluid with density of 1.018 g/cm and a viscosity of 0.0588 g/cm/sec (5.88 cps). The tank used in the manufacturing of the pilot batch had the following parameters ... 

This method can be easily used to show the logic behind the scale-up from original R D batches to production-scale batches. Although scale-of agitation analysis has its limitations, especially in mixing of suspension, non-Newtonian fluids, and gas dispersions, similar analysis could be applied to these systems, provided that pertinent system variables were used. These variables may include superficial gas velocity, dimensionless aeration numbers for gas systems, and terminal settling velocity for suspensions. 

Upon determination of design settling velocity, one must choose the scale of agitation required using Table 5 (9), which serves as the suspension products equivalent of Table 3. 

Chosen scale of agitation is then plugged into the Figure 3 chart to find the value of constant (p. 

The level of agitation is very important to the mechanics of suspension. Chemineer Inc. developed a scale of agitation from 1 to 10, summarized by Gates and al. (1976) as in Table 7-9. Figure 7-40 shows the level of suspension of sohds in correlation with the Chemineer scale. Often, manufactures define mixing as simple, mild, medium, vigorous, or violent (Figure 7-40). 

To correlate between the levels of agitation in a tank, the speed of rotation, and diameter of the impeller. Gates et al. (1976) plotted the scale of agitation versus , a factor defined in U.S. units as ... 

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