Studying the Avalanching Behaviour of a Powder in a Rotating Disc

Abstract

The use of a rotating disc to study the avalanching behaviour of a powder is discussed. It is shown that the strange attractor plotted in discreet time maps summarizes useful information on the rheological behaviour of powders and powder mixtures. In particular it is shown that the avalanching behaviour is related to the particle size distribution of the powder and that one can study the changes in rheological behaviour as another powder is mixed with it. The strange attractor patterns generated are dependent upon the environmental conditions under which the experiments are carried out. For this reason the measurements are referred to as an assessment of the holistic powder rheoiogy. The potential use of the disc to study the holistic rheology of powder systems is outlined.

The Sevilla Powder Tester: A Tool for Characterizing the Physical Properties of Fine Cohesive Powders at Very Small Consolidations

“…For low-cohesive well-behaved granular materials, avalanches occur quite regularly with nearly uniform size and time spacing, whereas in the case of poorly flowing cohesive powders, the time spacing and size of avalanches shows a noisy behavior [24]. A rotating drum-based unit, developed by Kaye and coworkers [25], is now commercially available. In this device, avalanches are automatically detected by a change in the light intensity captured by a grid of photocells placed behind the drum.…”

Signal Processing and Analysis Applied to Powder Behavior in a Rotating Drum

“…The Aero-Flow has been utilized to demonstrate correlation between powder¯ow and tableting performance for like materials [14]. The instrument uses a photocell detector for its avalanche detection mechanism [8]. A light shines through the Plexiglas drum and is obscured from the detector to varying degrees by powder contained in the drum.…”

“…The introduction of a second size particle into the simulation destroyed the periodic behavior. Experimentally determined time series of avalanches have been shown to exhibit complex periodicity using the concepts of chaos theory [8,9]. Rotating drum studies were used in applications for powder and process characterization [10,11] and to determine powder mixing effects in the drum [12,13].…”

Behavior of cohesive powder in rotating drums

“…Granular materials and powders are important raw materials for various commercial applications, e.g., in the agricultural, geotechnical, pharmaceutical, chemical and food processing industries [1,2,3]. An important challenge is the accurate characterization of the deformation and flow behavior of cohesive powders under static and dynamic conditions, as related to storage, handling and processing.…”

“…When they are subjected to quasi-static deformations (in the macroscopic sense), one can measure the relationships between stress and strain at moderate and high compression stress levels [4]. For low stresses, close to the surface of the bulk material, since decades, laboratory tests in rotating drums have been used to understand the dynamic and shear behavior of particulate materials [2,5,6,7]. Various rotation regimes can be realized involving very slow, avalanching and very fast, centrifuging regimes.…”