From Quasi-static to Intermediate Regimes in Shear Cell Devices: Theory and Characterisation

Abstract

The design of new technology for processing and manufacturing particulate products requires understanding granular rheology over a broad range of conditions. Powders display a complex behaviour due to their ability to rearrange under stress, and as a result, granular flow is generally classified into three flow regimes, namely a quasi-static regime dominated by frictional contacts, an inertial regime dominated by collisional and kinematic stresses and an intermediate regime where the three sources of stress are important to establish a stress-strain rate relationship. Characterisation of the flowability is generally restricted to the flow initiation in quasi-static regime, even if, transition into inertial conditions is very common in practical applications involving the control of dense flows, such as powder handling, particle formation processes or additive manufacturing. This work presents a critical review of available techniques to characterise the departure from the quasi-static regime into an intermediate flow. We revise the application of shear cells and present different strategies to modify classic devices with external actuation, such as aeration, to operate at higher inertial numbers. We pay particular attention to innovative designs using aerated Couette flow configurations, highlight the complexity in the standardisation and the challenges in advancing towards a universal model.

Impact of Powder Properties on the Rheological Behavior of Excipients

“…The lack of overlap in powder ranking by these measurements is explained by differences in the flow fields of these measurements. Hausner ratio and shear cell consider a quasi-static flow field [ 33 ], while the cohesive index at 60 rpm measures powder flow in a dynamic flow field. Observed differences are in line with Lumay et al [ 23 ], who showed that different flow regimes were influenced by different material properties.…”

Powder flow behavior governed by the surface properties of glass beads

“…In the literature, a vast body of researches conducted to study the powder flow behavior by different shear cell tests [48][49][50][51][52][53]. In our previous study we studied flowability of raw and hydrophobic glass beads with shear cell [31].…”

The Effect of Process Conditions on Powder Flow Properties for Slow Flow Regimes

“…First, different flow regimes ranging from slow to intermediate and rapid exhibit very different phenomena and, therefore, are described by peculiar models that relate solid stress and velocity fields depending on the relevant strain rates. Boundaries between different regimes were proposed in terms of dimensionless inertial number as the ratio between the time scale associated with the consolidation stress and the time scale of the strain, as summarised in recent comprehensive surveys (Francia et al, 2021;Mort et al, 2015). Therefore, all these regimes will not be covered in this review work.…”