Packing grains by thermal cycling

Abstract

One of the oldest and most intriguing problems in the handling of materials is how a collection of solid grains packs together. 1 While granular packing is normally determined by how grains are poured or shaken, we find that a systematic and controllable increase in packing is induced by simply raising and lowering the temperature, e.g., without the input of mechanical energy. The results demonstrate that thermal processing provides a largely unexplored

Correlation between Particle Motion and Voronoi-Cell-Shape Fluctuations during the Compaction of Granular Matter

“…2 with ρ 0 = 0.619 ± 0.0008, A = 0.028 ± 0.0007, and τ = 4.87 cycles ± 0.31 cycles. The compaction rate is slower than the faster of the two time scales, 2.72 cycles, reported by [11], consistent with a weaker forcing of the particles due to buoyancy forces.…”

“…This is the same materials as used in previous work on thermal cycling [11]. The thermal expansion coefficient for PMP is 1.17 × 10 −4 K −1 , about one order of magnitude larger than that of the beads (9 × 10 index-matching oil (Cargille Labs Type DF [20]) which contains 2.08 µg/mL laser dye (Nile Blue 690 perchlorate).…”

“…By thermal cycling we meanalternately heating and cooling the material and container, with one heating and cooling cycle corresponding to one perturbation. This technique leads to exponential compaction of the material with two characteristic timescales [11] if the granular material and container have different thermal expansion coefficients. While most methods of forcing rearrangements of granular matter, such as tapping of the boundaries or air fluidization agitate individual particles significantly, i.e.…”

Enhancing soil sample preparation by thermal cycling

“…The top surface of the sample was found to be fairly levelled after thermal cycling, which is in part related to the effect of the dead weight, but also suggests that packing densification is a bulk effect rather than a boundary effect; this has also been observed by Chen et al (2006). The densification was assessed in terms of relative density, D r = (e max À e)/(e max À e min ) Â 100.…”

“…This work draws upon previous studies on the dynamics induced by thermal cycling on granular media (Chen et al, 2006;Percier et al, 2013). The rise in temperature results in a thermal expansion of the grains and the container, which causes the granular assembly to settle and densify.…”