Repeated segregation and energy dissipation in an axially segregated granular bed

Abstract

-Discrete element simulations were used to study the segregation behaviour in a bed of bidisperse granules in a rotating drum. In the final state the large particles ended up in the upper part of the bed near the vertical walls. In order to arrive at this state, the system went through two cycles of structural changes, on top of which fast oscillations were observed between an axially segregated and a somewhat more mixed state. These oscillations were sustained by different angles of repose near the vertical walls and in the middle of the bed. Concomitantly with the structural changes, the system's energy dissipation went through two cycles after which it settled in the state requiring the least work of all traversed states, suggesting that the granular bed strives for minimal dissipation.

Alignment of particles in sheared viscoelastic fluids

“…Since the rate of energy dissipation by the sheared fluid is given by P = S xyγ L z , the decreasing shear stress may be re-interpreted as an evolution of the colloidal suspension towards a steady state requiring minimum power dissipation. Interestingly, we observed similar relaxations to steady states of minimum dissipation in several system that we studied recently, including shear-banding of a viscoelastic fluid in the RaPiD simulations 27,40 and segregation of granules in a rotating drum, 47 which tentatively suggests that a reduction of the dissipation rate may act as a driving mechanism inducing ordering in driven systems. For an extensive discussion on possible generic physical laws governing non-equilibrium J. Chem.…”

Segregation of granular particles by mass, radius, and density in a horizontal rotating drum

“…In long drums, the initial radial segregation is followed by a slow axial segregation, giving rise to stripes perpendicular to the drum's axis that gradually diffuse and merge over time . The role of the drum's end‐walls in initiating this transition, especially in narrow drums, has recently attracted attention . Interestingly, the power consumption of a drum rotating at constant angular velocity was recently observed to correlate with the order of the granular bed in that drum .…”

“…The role of the drum's end‐walls in initiating this transition, especially in narrow drums, has recently attracted attention . Interestingly, the power consumption of a drum rotating at constant angular velocity was recently observed to correlate with the order of the granular bed in that drum . Despite the extensive research and industrial relevance of segregation in tumbling blenders, to quote a recent paper: “its mechanisms are not clearly understood and all known theories or explanations have exceptions.” In this context, it is interesting to note that certain systems appear not to converge to a steady state, but to alternate randomly between two metastable states …”

Simulations of flow induced ordering in viscoelastic fluids

“…The evolutions of the shear stresses S xy in the pure fluid and the suspension are plotted states of minimum dissipation in several system that we studied recently, including shearbanding of a viscoelastic fluid in RaPiD simulations [115,116] and segregation of granules in a rotating drum [5], which tentatively suggests that a reduction of the dissipation rate may act as a driving mechanism inducing ordering in driven systems. For an extensive discussion on possible generic physical laws governing non-equilibrium steady states, and the evolution toward these states, we refer the reader to the review of Martyushev and Seleznev [77] and the book byÖttinger [85].…”

“…the density of a solvent-free polymer melt, and therefore φ i ≤ 1. Using the procedure described in Appendix 2.5, we can approximate the total free energy of the system, for a given configuration r, as a sum of particle contributions 5) where the free energy per chain, as a function of the local chain density, reads as…”