University of Natural Resources and Life Sciences, Vienna (BOKU) - Research portal
Gewählte Doctoral Thesis:
John Mathews
(2013):
Investigation of granular flow using silo centrifuge models.
Doctoral Thesis - Institut für Geotechnik (IGT),
BOKU-Universität für Bodenkultur,
pp 234.
UB BOKU
obvsg
FullText
- Abstract:
- Silos have multiple applications in practice. Silo discharge and silo wall pressures have been investigated for over a century, but many features of silo design and operation are only partially understood. The velocity field within the silo during discharge cannot be reliably predicted yet, and the mechanisms controlling discharge remain unclear. This thesis presents an investigation into gravity discharge from silos in increased gravity conditions. Flow conditions and lateral wall pressures are quantified. A review of silo centrifuge modelling and silo discharge under the action of gravity is also presented. It is shown that the mass flow rate is proportional to the square root of the gravity and that the width of the flow channel at any given height above the outlet is independent of gravity. The local velocity of discharging material is also proportional to the square root of the gravity. These observations show that the angle at which a stagnant zone intercepts a silo wall is independent of gravity and that the criteria for funnel or mass flow conditions are independent of gravity. Analysis of the time required to discharge the silo leads to the observation of a scaling law for silo centrifuge models, which is useful for centrifuge models involving granular flows. In a silo model discharging cohesionless material, time scales with gravity according to the following law: t_m=t_p N^{-1/2} Force Sensing Resistors (FSRs) are used to measure normal pressure across the silo walls. The performance of the FSR arrays is assessed by investigating normal pressures before and during discharge. The FSR instrumentation does not distinguish between normal and shear forces and this influences the readings, however qualitative and in some cases quantitative agreement with Janssen's wall pressure theory based on continuum assumptions was found.
- Betreuer: Wu Wei