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IAS & WUN Seminar Series Wednesday, November 28 Granular Flows I Herbert Huppert

IAS & WUN Seminar Series Wednesday, November 28 Granular Flows I Herbert Huppert. Granular Flows. Powders < 0.1mm < grains < 1 cm < rocks ~ 10m. Foods: cereals, fertilizers, sweets, salt, sugar Pharmaceuticals: pills, drugs

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IAS & WUN Seminar Series Wednesday, November 28 Granular Flows I Herbert Huppert

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  1. IAS & WUN Seminar Series Wednesday, November 28 Granular Flows I Herbert Huppert

  2. Granular Flows Powders < 0.1mm < grains < 1 cm < rocks ~ 10m • Foods: cereals, fertilizers, sweets, salt, sugar • Pharmaceuticals: pills, drugs • Earth sciences: rock falls, mud slides, snow avalanches • Civil engineering: cement, concrete, rubble • Chemical engineering: catalytic particles • Mining engineering: ores Examples

  3. Examples

  4. Granular Flows Difficult to understand: (much) more difficult than fluid flows • Theory (no general equations) • Computer simulations • Laboratory experiments • Industrial plants

  5. From Nico Gray

  6. From Nico Gray

  7. Coulomb friction (1736 – 1800) Experiments show friction force approximately: independent of contact area or velocity; but dependent on pairs of materials. stick slip but can be much lower: metal on metal or much higher: plastic wrap on lettuce good approximation; not perfect

  8. Friction angle Block at rest on plane with angle At rest: maximum friction angle or angle of repose

  9. Statics Volume fraction of grains equal sized spheres: • maximum density or at hexagonal packing (Kepler, Gauss, Hales) • random close packing • random loose packing

  10. Two sizes of spheres: small and large Total volume fraction Fraction of large

  11. The red regions mean large local force; the blue regions weak local force. The stress chains show in red. The forces detected by photoelasticity

  12. Simple granular flows

  13. sugar sand couscous rice salt

  14. Vanel et al. Phys Rev E 1999

  15. General Ralph A. Bagnold F. R. S.

  16. Bagnold number : density of particle, of radius a : shear rate ( ) : (dynamic) viscosity of fluid

  17. Contents • Motivation • Simple granular flows • Collapses in the laboratory • Theoretical descriptions • Conclusions With Gert Lube & Steve Sparks

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