Abstract
Granular materials in rotating drums are of wide interest not only because of their extensive use in the industrial contexts, but also as model systems in the study of natural disasters, such as avalanches or landslides. Most of available experimental methods are restricted to surface layer flows and dilute systems whilst the remainder can only resolve the granular dynamics to a fine scale with relatively poor temporal resolution or vice versa. In contrast, speckle visibility spectroscopy (SVS) is able to resolve the average of the three components of motion of grains in dense systems in small volume of granular media several layer deep with spatio-temporal resolutions that allow the probing of the granular micro-dynamics. We have used this technique to study granular dynamics of surface avalanche flow in the slumping regime using both spherical glass and irregular sand particles. Although results are very similar, we determined that visually observed compaction at the beginning of avalanche process for irregular sand particles influence time evolution of the particle fluctuation velocity during avalanches.
Highlights
Granular flows in rotating drums are of wide interest as model systems in the study of the physics of granular media, and because of their extensive use in the chemical, minerals, pharmaceutical and food industry where they are employed to effect process as diverse as mixing and granulation
There are a range of experimental methods available for the study of the granular dynamics in rotating drums, including particle image velocimetry (PIV) [4,6,7,8], particle tracking velocimetry (PTV) [9,10], PEPT [11,12], magnetic resonance imaging [13,14], and x-ray microtomography [15]
Some of these are restricted to two components of motion (PIV and PTV) whilst the remainder can only resolve the granular dynamics to a fine scale with relatively poor temporal resolution or vice versa
Summary
Granular flows in rotating drums are of wide interest as model systems in the study of the physics of granular media, and because of their extensive use in the chemical, minerals, pharmaceutical and food industry where they are employed to effect process as diverse as mixing and granulation. There are a range of experimental methods available for the study of the granular dynamics in rotating drums, including particle image velocimetry (PIV) [4,6,7,8], particle tracking velocimetry (PTV) [9,10], PEPT [11,12], magnetic resonance imaging [13,14], and x-ray microtomography [15] Some of these are restricted to two components of motion (PIV and PTV) whilst the remainder can only resolve the granular dynamics to a fine scale with relatively poor temporal resolution or vice versa. Diffusing-wave spectroscopy [16], a dynamic light scattering technique, is able to resolve the average of the three components of motion of grains in dense systems with very fine spatiotemporal resolutions [17,18] that allow the probing of the dynamics of avalanches It is based on temporal correlation functions calculated as a time average, so it is not appropriate for systems with transient dynamics. The related method of speckle visibility spectroscopy (SVS) [5,19,20,21] can be used
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