Lean Phase Flow - Twin-Screw Feeder
When considering powder flow in different pharmaceutical processes, it must be recognised that a number of different powder flow regimes can arise from the interaction of the powder with the internal process mechanisms. Therefore, it is prudent that the EPF is integrated into different processes and flow regimes, with the interests in the potential development of the technology as a universal process-analytical tool.
In a screw feeder, powder becomes entrained to the rotation of the screws (Fig. 1), which results in a pulsatile delivery under a lean phase flow regime. In this system (Fig. 2), the EPF sensor is used to measure the electrostatic flow ‘noise’ of powder deposited by a volumetric twin-screw feeder, and an electronic balance is used to measure the mass flow.
The periodicity in the powder flow lends itself to the application of other data processing techniques such as Fourier Analysis, which can provide the flow pattern of the powder entrained to the twin-screw feeder mechanisms.
Fig.2. Schematic of lean phase powder flow measurement system
(twin-screw feeder, EPF and balance)