The particle contacts in different particle-fluid flow regimes, such as fixed, expanded and fluidized beds, in gas fluidization are investigated for group A and B powders by means of a combined approach of computation...
The particle contacts in different particle-fluid flow regimes, such as fixed, expanded and fluidized beds, in gas fluidization are investigated for group A and B powders by means of a combined approach of computational fluid dynamics anddiscrete element method. To establish the connection between macroscopic and microscopic descriptions of complex particle-fluid flows, focus is given to the correlation between coordination number (CN) and porosity (ε). It is found that the CN-ε relationship for group A powders has a transitional point between the expanded and fluidized bed flow regimes at a bulk scale, unlike group B powders. A new phase diagram is established in terms of CN-ε relationship that has two branches representing expanded and fluidized (bed) states.
This paper presents a structural analysis on the packing of monosized spheres in terms of Voronoi clusters. The packings considered were generated by the discrete element method, with packing densities ranging from 0....
This paper presents a structural analysis on the packing of monosized spheres in terms of Voronoi clusters. The packings considered were generated by the discrete element method, with packing densities ranging from 0.2 to 0.74. The Voronoi clusters are composed of center particles and their neighbouring particles, which can be used to characterize the local packing structures in terms of the topological connections between particles, to be beyond the metric and topological properties of individual polyhedra as done previously. The types and distribution of clusters, together with coordination number and common geometrical neighbours determined by Voronoi polyhedra are quantified as a function of packing density. Random close packing is shown to correspond to a turning point of these evolutions.
Heat transfer in gas fluidization is investigated at a particle scale by means of a combined discrete element method and computational fluid dynamicsapproach. To develop understanding of heat transfer at various condi...
Heat transfer in gas fluidization is investigated at a particle scale by means of a combined discrete element method and computational fluid dynamicsapproach. To develop understanding of heat transfer at various conditions, the effects of a few important material properties such as particle size, the Hamaker constant and particle thermal conductivity are examined through controlled numerical experiments. It is found that the convective heat transfer is dominant, and radiative heat transfer becomes important when the temperature is high. Conductive heat transfer also plays a role depending on the flow regimes and material properties. The heat transfer between a fluidized bed and an immersed surface is enhanced by the increase of particle thermal conductivity while it is little affected by Young’s modulus. The findings should be useful for better understanding and predicting the heat transfer in gas fluidization.
We present a brief overview of a method which can identify different 3D local structures in ordered and disordered systems. Its effectiveness is demonstrated in the analysis of the structures of sphere packings, the s...
We present a brief overview of a method which can identify different 3D local structures in ordered and disordered systems. Its effectiveness is demonstrated in the analysis of the structures of sphere packings, the structural evolution of a rapid cooling process of silver liquid, and the inner structure of a metal nanocluster. Quantifying local structures by means of a topological criterion, this method is parameter-free and scale-independent, and can generally be used for structural analysis of amorphous systems involving atoms or particles at different length scales.
Granular flow in rotating drums exhibits complex phenomena which are further complicated by the presence of liquids. This paper reviews our recent work on flow of wet particles in rotating drums based on the discrete ...
Granular flow in rotating drums exhibits complex phenomena which are further complicated by the presence of liquids. This paper reviews our recent work on flow of wet particles in rotating drums based on the discrete element method (DEM) simulations. The DEM model was validated by comparing the simulation results with experimental measurements. Particle flow at quasi-static and dynamic states was investigated. In the quasi-static state with the drum rotating at low speeds, wet particle bed failed through avalanche and slow structural change was identified prior to the avalanches. In the dynamic state, flow transited from continuous to avalanche flow with increasing liquid surface tension and a plug flow was developed on the bed surface. Particle mixing in both transverse and axial directions was studied. While cohesion in general reduced transverse mixing, enhanced mixing of wet particles was also observed, which was explained by a theory based on particle circulation period. On the other hand, the axial mixing was well described by Fick’s law of diffusion and particle diffusivity decreased with increasing cohesion. A correlation was observed between particle diffusivity and granular temperature.
This paper presents a numerical study on the piling processes of mono-sized wet particles by the discrete element method (DEM). The capillary force between particles due to liquid bridge is implemented in an existing ...
This paper presents a numerical study on the piling processes of mono-sized wet particles by the discrete element method (DEM). The capillary force between particles due to liquid bridge is implemented in an existing DEM model. The effects of moisture content on the repose angle and structure of a pile are studied by a series of controlled numerical experiments. It is confirmed that the structure of a pile is similar to that of a packing for cohesive particles. Moreover, the averaged local porosity and repose angle have similar changes with the moisture content and can be linearly correlated. Therefore, the relationship between the repose angle and the cohesive force can be established based on the previous correlation between the porosity and the force ratio of the cohesive force to gravity developed in the packing of cohesive particles.
A three-dimensional CFX-based mathematical model is developed to describe the flow-heat transfer-chemical reactions behaviours of gas-solid-liquid phases in an ironmaking blast furnace (BF), where the raceway cavity i...
A three-dimensional CFX-based mathematical model is developed to describe the flow-heat transfer-chemical reactions behaviours of gas-solid-liquid phases in an ironmaking blast furnace (BF), where the raceway cavity is considered explicitly. The typical in-furnace phenomena of an operating blast furnace, in particular, the liquid flow in the lower part of a blast furnace is simulated in aspects of velocity and volume fraction. This model offers a cost-effective tool to understand and optimize blast furnace operation.
In order to understand the complex phenomena of pulverized coal injection (PCI) process in blast furnace (BF), mathematical models have been developed at different scales: pilot-scale model of coal combustion and indu...
In order to understand the complex phenomena of pulverized coal injection (PCI) process in blast furnace (BF), mathematical models have been developed at different scales: pilot-scale model of coal combustion and industry-scale model (in-furnace model) of coal/coke combustion in a real BF respectively. This paper compares these PCI models in aspects of model developments and model capability. The model development is discussed in terms of model formulation, their new features and geometry/regions considered. The model capability is then discussed in terms of main findings followed by the model evaluation on their advantages and limitations. It is indicated that these PCI models are all able to describe PCI operation qualitatively. The in-furnace model is more reliable for simulating in-furnace phenomena of PCI operation qualitatively and quantitatively. These models are useful for understanding the flow-thermo-chemical behaviors and then optimizing the PCI operation in practice.
The pulverized charcoal (PCH) combustion in ironmaking blast furnaces is abstracting remarkable attention due to various benefits such as lowering CO2 emission. In this study, a three-dimensional CFD model is used to ...
The pulverized charcoal (PCH) combustion in ironmaking blast furnaces is abstracting remarkable attention due to various benefits such as lowering CO2 emission. In this study, a three-dimensional CFD model is used to simulate the flow and thermo-chemical behaviours in this process. The model is validated against the experimental results from a pilot-scale combustion test rig for a range of conditions. The typical flow and thermo-chemical phenomena is simulated. The effect of charcoal type, i.e. VM content is examined, showing that the burnout increases with VM content in a linear relationship. This model provides an effective way for designing and optimizing PCH operation in blast furnace practice.
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