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The research of physicist Arshad Kudrolli and his students on the properties of granular matter can provide clues about how substances as diverse as sand and face powder behave. |
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Granular Matter
Size segregation of granular matter in silo discharges
Azadeh Samadani, Apurba Pradhan and Arshad Kudrolli
We study the flow properties of granular material through an orifice in a
two-dimensional glass container using high-resolution imaging. Figure 1 illustrates how
the granular matter (glass beads) empties from a orifice at the bottom on the container
(silo). Two phases are observed: a static solid-like region, and a rapidly flowing
fluid-like region.
We utilize digital imaging to obtain the interfaces of the static and moving regions as
well as the surface profile as the material is emptied. Click to view a movie of surface instability observed at high
flow rates. The width of the viewing region is 3 inches and the orifice is 1 inch wide.
The surface is observed to deviate strongly from the approximately linear profile observed
at low flow rates.
Figure 2 illustrates how particles segregate according to size with larger particles
being found at the center in the region of fastest flow. We have quantitatively
investigated the development of segregation as a function of time and as a function of
size ratio of the particles and the flow rate [1,2].
Publications
1.`"
Size Segregation of Granular Matter in Silo Discharges," A.
Samadani, A. Pradhan, and A. Kudrolli Physical Review E 60, 7203 (1999).
2."Visualization of segregation in granular flows inside silos," A.
Samadani, A. Pradhan, and A. Kudrolli, The Proceedings of The ITUAM Symposium on Segregation in
Granular Flows, (Kluwer Academic Publishers, 2000) p. 53.
Segregation transitions in wet
granular matter
Azadeh Samadani and Arshad Kudrolli
Segregation in granular matter can be benefit or a nuisance. Remarkable sensitivity to
small differences in the size, shape and density of the constituent grains has been
observed. However, most of this work relates to noncohesive granular matter. We
investigate the progress of segregation in the presence of interstitial fluid by imaging
the pile that results after bidisperse color-coded particles are poured into a silo. A
sharp reduction of segregation is observed when a small volume fraction of fluid V_f is
added which introduces capillary bridges between particles. Preferential
clumping of small particles is observed to cause layering at small V_f. We obtain the
segregation phase diagram as a function of size ratio r of the bidisperse particles and
V_f. We show the importance of the viscous force in addition to the capillary force on
both the progress of segregation and the angle of repose theta by changing the viscosity
of the fluid. We find that the sharp change in the extent of segregation and theta occurs
over similar V_f. A second transition to segregation depending on viscosity is observed
when the particles are completely immersed in the fluid.
Publications
1. "Segregation transitions in wet granular matter," A. Samadani and A.
Kudrolli, Physical Review Letters, 85, 5102 (2000). (Preprint on
cond-mat/0008293) .
Research funded by the National Science Foundation and
the donors of the Petroleum Research Fund.
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Additional Resources
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Figure 1: The granular matter (glass beads) empties from an orifice at the bottom.
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Figure 2: Particles size segregate. Larger particles were found at the center.
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Figure 3: The effect of adding a small volume fraction of fluid to bidisperse glass beads. (a) corresponds to the dry case and (d) where 1% by volume of water has been mixed into the granular mixture before pouring. |
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