Relative swept volume

Scale-Up and Operation Scale-up of pharmaceutical mixer granulators is difficult because geometric similarity is often not preserved. Kristensen recommends constant relative swept volume ratio... 

A third equipment parameter is the relative swept volume (RSV). 

Relative swept volume, that is, the volume swept by the impeller (and chopper) per unit time, divided by the mixer volume, has been suggested as a scale-up factor. This parameter is related to work done on the material and was studied extensively at various blade angles. Higher swept volume leads to higher temperature and denser granules. However, it was shown by Horsthuis et that the same relative... 

The area under the torque-time curve is related to the energy of mixing and can be used as an end-point parameter. Area under power consumption curve divided by the load gives the specific energy consumed by the granulation process. This quantity is well correlated with the relative swept volume. ... 

The consumed energy is completely converted into heat of the wet mass, so that the temperature rise during mixing shows some correlation with relative swept volume and Froude number that relates the inertial stress to the gravitational force per unit area acting on the material. 

In a seminal and elegant work published in 1993, Horsthuis et al. from Organon in The Netherlands have studied granulation process in Oral mixers of 10, 75, and 300 L size. Comparing relative swept volume, blade tip speed and Froude numbers with respect to end-point determination (as expressed by the time after which there is no detectable change in particle size), they have concluded that only constant Froude numbers result in a comparable end-point. 

For many commercial mixers, since geometric similarity is often not preserved—even within a given manufacturer—Kristensen recommends constant relative swept volume ratio Vas a scale-up parameter as a starting point, defined as... 

Historically, mixer granulators have been more commonly scaled up using constant tip speed or constant relative swept volume (25,27). Maintaining constant... 

The constant swept volume approach to scale-up was introduced partly to account for variations in geometry on scale-up. The relative swept volume is defined as... 

---