The storage of granular materials is a critical process in industry, which has driven research into flow in silos. Varying material properties, such as particle size, can cause segregation of mixtures. This work seeks to elucidate the effects of size differences and determine how using a flow-correcting insert mitigates segregation during silo discharge. A rotating table was used to collect mustard seeds discharged from a three-dimensional (3D)-printed silo. This was loaded with bidisperse mixtures of varying proportions. A 3D-printed biconical insert was suspended near the hopper exit to assess its effect on the flow. Samples were analysed to determine the mass fractions of small particle species. The experiments without the insert resulted in patterns consistent with segregation. Introducing the insert into the silo eliminated the observed segregation during discharge. Discrete element method simulations of silo discharge were performed with and without the insert. These results mirrored the physical experiment and, when complimented with coarse graining analysis, explained the effect of the insert. Most of the segregation occurs at the grain-air free surface and is driven by large velocity gradients. In the silo with an insert, the velocity gradient at the free surface is greatly reduced, hence, so is the degree of segregation.

Storage and Flow of Solids

Granular size segregation in silos with and without inserts

Hopper systems of different shapes and sizes are widely used
in bulk solids industries to store and further process the particulate
material. Poor hopper design causes variety of problems and results in wastage
of resources. This dissertation investigates the applicability of finite
element method (FEM) based continuum modeling in predicting flow
characteristics of particulate materials discharging through hopper system. Throughout
the years, FEM has been implemented to simulate the shear failure of particulate
materials such as sand, glass beads, and pharmaceutical powders. The FEM
framework is based on the underlying constitutive model. Different constitutive
models are available in the literature to govern the behavior of particulate
materials. These models differ in their complexity, ease of implementation, and
have specific strengths and limitations. This work thoroughly investigates the
elasto-plastic constitutive models available in the commercial software Abaqus
in the context of hopper flow of particulate materials.

The thesis consists of three major parts, first part deals
with FEM modeling of cohesionless particulate materials and corresponding
verification of the hopper flow characteristics through comparison to
analytical theories and empirical correlations. The second part presents
quantitative comparison of FEM predicted flow characteristics to experimental
results for Ottawa sand discharging through concentric and eccentric bins. Particle
image velocimetry (PIV) experiments are conducted on a laboratory-scale bin to quantify
different flow characteristics. The last part deals with cohesive particulate
materials and presents a novel FEM approach for predicting the critical hopper
outlet opening to ensure uninterrupted discharge of the stored material.

This thesis concludes that the FEM modeling based on simple elasto-plastic
constitutive model proves useful in predicting different hopper flow
characteristics of particulate materials. The accuracy of FEM modeling depends
on detailed material characterization and corresponding implementation in Abaqus.
Some modifications need to be made in the elasto-plastic constitutive models to
accurately represent the bulk material behavior. The ideas presented in this
thesis can be applied to FEM modeling of other processing equipment such as the
rotating drum, screw-feeder, rotating blender/mixer etc.

Finite Element Method (FEM) Modeling of Hopper Flow

This chapter presents preliminary numerical results of different quasi-static boundary value problems in granular bodies including shear localization. Calculations were carried out with the finite element method on the basis of a micro-polar hypoplastic model. The following problems were considered: plane strain compression test, monotonic and cyclic shearing of an infinite layer, biaxial compression test, strip foundation, earth pressure, direct and simple shear test, wall direct shear test and contractant shear zones. Attention was paid to the thickness and spacing of shear zones. Numerical solutions were compared with corresponding laboratory tests.

Finite Element Calculations: Preliminary Results

Composition of bulk solid discharged from a bin with continuous recirculation

/pdf/diseno-de-un-sistema-de-molienda-de-carbon-mineral-para-ser-u0pi50b4ce.pdf

Storage and Flow of Solids

Citations

Granular size segregation in silos with and without inserts

Finite Element Method (FEM) Modeling of Hopper Flow

Finite Element Calculations: Preliminary Results

Composition of bulk solid discharged from a bin with continuous recirculation

Diseño de un sistema de molienda de carbón mineral para ser usado como combustible industrial

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