Dynamics of segregation of dry and liquid granular systems in quasi-two-dimensional (2D) and long (2D+1) tumblers.

Abstract

The focus of this thesis is the interplay of mixing and size segregation of bi-disperse granular materials in dry granular systems (DGS), where particles are surrounded by air, and liquid granular system (LGS), where air is replaced with a liquid. The systems are periodically forced quasi-2D tumblers and long tumblers, referred as 2D+1. The 2D cases focus on radial segregation and lobe formation; the 2D+1 cases focus on axial segregation and band coarsening. The 2D periodically forced tumbler is studied experimentally and numerically using a continuum model. Experiments in DGS and LGS produce similar segregation patterns, display qualitatively similar dynamic behaviors, and are in good agreement with Poincare mappings from numerical simulations. Axial segregation of DGS in 2D+1 systems is examined in tumblers of circular and square cross sections. Depending on the cross section and rotational speed, a variety of different bands dynamics exist including band formation, merging, and splitting. However, the area of surface bands after an initialization period is nearly constant in all systems studied leading to quasi-one-dimensional behavior. Also, when band coarsening does occur, the number of bands decays logarithmically. LGS---in the parameter range studied---exhibit 'typical' band dynamics: bands form during an initialization period and then coarsening may or may not occur. Parameters can alter the time for bands to form, the number of bands that form, and how fast bands merge, but the overall qualitative dynamics do not change. In LGS bands form slightly faster in tumblers with circular cross section than square cross section, but the number of bands and the rate of merging are virtually identical. At faster rotation rates and higher interstitial fluid viscosities bands form quicker in LGS, but bands of smaller particles become more contaminated with larger particles. LGS experiments scale linearly with the tumbler length but the intrinsic dynamics of the bands do not change. Results from tumbler rocking experiments indicate that the maximum number of bands decreases with higher rocking amplitude, but the rate of merging and the area of bands is largely unaffected. Source: Dissertation Abstracts International, Volume: 67-03, Section: B, page: 1560. Adviser: Julio M. Ottino. Thesis (Ph.D.)--Northwestern University, 2006.