Materials In Hoppers Research Articles

Discrete element modeling of deformable pinewood chips in cyclic loading test

The design of efficient lignocellulosic biomass feedstock systems is challenging, as current laboratory characterization and design methods were developed primarily for fine powders with relatively low compressibility. The discrete element method (DEM) is gaining prominence as an alternative method for modeling the bulk flow and transport of particulate materials in hoppers and feeders. However, prior DEM simulations investigating the flow of wood chips modeled the particles as simple rigid geometries such as spheres, rods or blocks, and neglected the effects of particle deformability and irregular shapes. As a consequence, those simplified DEM models may not provide enough key diagnosis to help improve the design of biomass feeding and handling equipment. This work presents a bonded-sphere DEM approach for characterizing the mechanical behavior of bulk flexible, deformable pinewood chips in a cyclic stress loading test. Clustered spheres that can bend and twist via elastic bonds are used to model irregular-shape particles in real pinewood chip samples. An axial compression tester, which contains 0.06 million bonded-sphere particles (1.35 million spheres) in a quarter cylinder, is simulated with a domain size similar to the experiments. With careful calibration, the simulations have delivered the bulk densities and the bulk moduli of elasticity that are in good agreement with those measured in the corresponding experiments. However, it is also been found challenging for the present DEM model to accurately predict the overall stress-strain behavior of bulk pinewood chips, especially the large sustained plastic deformation during unloading. Additional numerical tests have shown that the adjustment in certain contact parameters (e.g. bond stiffness) can lead to profound solution improvement, but meanwhile will induce extra challenges such as increased computing time. Future work will include an elasto-plastic particle bond model to enhance the simulation fidelity.

Deformation Zones in Granular Materials in Hoppers During Filling and Emptying Processes

The present paper is concerned with the simplified analysis of deformation and stress states in converging hoppers during filling and discharge of a granular material. The equilibrium conditions and stress-strain relations are satisfied for cylindrical slice elements assuming dependence of displacement and stress on radial coordinate. The elastic or elasto-plastic material model is used with the Coulomb yield condition and non-associated flow rule. The paper presents a detailed analysis of pressure evolution of a granular material on a hopper wall during the emptying process when the initial active state of pressure is transformed into the passive state. The growth of wall pressure associated with this process is demonstrated. The analytical treatment presented in this paper can be compared with the respective finite element solution.

Numerical determination of flow corrective inserts for granular materials in conical hoppers

The flow of granular materials in hoppers is studied. In industrial applications, inserts of various sizes and shapes are often used to improve the flow properties and get rid of undesirable effects such as material sticking to the walls, funnel flow, arching, etc. We study the case of inverted conical inserts in conical hoppers. In spite of the complexity of the phenomenon as observed in practice, existing methods assume in general a radial structure of the stress and velocity fields. A new numerical approach to the problem of designing “optimal” inserts is proposed and tested. It allows for non-purely radial solutions. General comments about the overall approach and its relationship with experiments are offered.

Some aspects of flow in granular materials in hoppers

The main part of the paper is devoted to the description of the localized deformation zones in plane (slow) flow of granular materials from hoppers. Specifically, two types of zones are discussed i...

Numerical simulation of pattern formation in grain flows

We present numerical computations for the flow of granular materials in hoppers. The algorithm is based on a cellular automaton approach and takes into account various microscopic effects, including “orientational effects”. The formation and the dynamics of density waves, recently discovered in physical experiments, is observed and analyzed computationally.

Pneumatic stirring system for loose materials in hoppers

Pneumatic stirring system for loose materials in hoppers

Gravity flow of granular materials in Hoppers and bins in mines—II. Coarse material

Gravity flow of granular materials in Hoppers and bins in mines—II. Coarse material

Gravity flow of granular materials in hoppers and bins

Gravity flow of granular materials in hoppers and bins