Mechanics of Dry Granular Flow through an Opening

Abstract

Granular flow is a historical study which has been widely investigated experimentally, analytically and numerically in last decades. This topic has been discussed in several disciplines, e.g., in Chemical engineering to study granular discharge rate in silos and hoppers or in Geotechnical engineering to study soil erosion. Hourglass as a time-keeping machine can be mentioned as a familiar granular flow application. In most studies grains have been assumed to be uniform sized particles and most analytical and numerical models are about this assumption. In nature, dealing with semi sized grains seems not to be factual, and particle size distribution is believed to play an essential role in granular flow, which has been ignored in most studies. This study aims at investigating the effect of particle size distribution (PSD) on the granular flow by experiments. This research studies the behavior of granular flow for non-uniform particle size conditions and free fall arch (FFA) formation. Some experiments were carried out with different particle size distributions to examine previously presented correlations. An attempt was made to identify and introduce the characteristic particle size based on experimentation on non-uniform particle size distributions for better prediction of granular flow rate with current correlations, although this attempt was not successful. For this study, two-dimensional granular flow was investigated through experimentation with granular flow through long-enough slots. A specific apparatus with variable and adjustable slot width was designed to be able to experimentally model and investigate the 2-D flow in different conditions. Sub-angular sand has been used as the granular material. For this thesis, the particle size, particle size distribution and slot width are the critical parameters in granular flow rate. It was confirmed that under non-uniform sized grain condition the independence of flow rate to granular height over the slot is still valid and in different size grain condition existence of free fall arch (FFA) is justifiable. Also, the granular flow rate is dominated by the finer portion of the PSD rather than the coarser grains. In the investigation of two correlations, one did not show any meaningful results whereas the other one showed an overestimation in comparison with experiments due to some simplifications in this formula, i.e., not considering the shape factor or simplifying the parameter of flowing density with minimum density.