Testing Velocity Scaling Criteria

Experimental work has not validated the scaling procedure above with respect to scale-up of blending processes. Since this approach also relies on empirical work, this model should not be favored over other approaches currently in use, though it may provide additional insights. 

All the vessels are constructed from clear plexiglas, enabling visual identification of segregation patterns. 

For these experiments, a binary mixture of sieved fractions of 150-250 pm (nominally 200 pm) and 710-840 pm (nominally 775 pm) glass beads was used. A symmetrical initial condition (top-to-bottom loading) is implemented. The blender is run at constant rotation rate a segregation pattern was assumed to be stable when it did not discernibly change for 100 revolutions. In many pharmaceutical operations, the mixing time is on the order of 100 500 revolutions, and experiments are run with regard to this timeframe. 

Blender size Transition rotation rate Fr, Sl R/g (xlO ) Tangential velocity, Q.R (cm/sec) (cm/sec) 

---

The Czechoslovak Standard CSN 640214 recommends that the test core method should be employed for determining the flowability of aminoplasts. The test core is stepped in shape. The flowability criterion is the time required to fill up the mould. The five-point scale for assessing the flowability is used. The average pressure on the material amounts to 54 1 MPa, the free-stroke velocity of the crosspiece of the press is 20 5 mm/s. 

Emulsion life expectancy for a formulation may be conservatively scaled up from 2-in. pipe-loop tests at the same velocity by demonstrating that the emulsion will survive transport for the desired actual distance in the pilot plant. Pilot-plant transport is a more severe test of emulsion life than transport in larger lines. The conservative nature of this scale-up criterion tends to dictate specification of some excess surfactant for a large-scale application beyond the minimum quantity required. 

---