Ali Hassanpour

A Study of Commercial Nanoparticulate γ‐Al2O3 Catalyst Supports

This study investigates a range of commercially available γ‐Al2O3 powders by using a combination of integrated experimental techniques. These included general measurements of powder properties by using helium density, BET surface area, and scanning electron microscopy (SEM) analyses. In addition, dynamic light scattering and zeta potential measurements were used to investigate nanoparticle dispersions. Bulk crystal structures were analysed by using comparative X‐ray and neutron powder diffraction (XRD and NPD) analyses. Conventional transmission electron microscopy (TEM) was used to determine particle morphology, particle size, composition, and structure. Aberration‐corrected TEM was used to investigate the crystallinity of nanoparticles including the existence of any surface reconstruction on commonly observed facetted, cubeoctahedral γ‐Al2O3 nanoparticles. From the observation of peak splittings in diffraction data, we favour a description of the γ‐Al2O3 structure based on a distortion of the conventionally accepted face‐centred cubic (Fd

Analysis of Tribo-Electric Charging of Spherical Beads Using Distinct Element Method

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Modeling of agglomerate behavior under shear deformation: effect of velocity field of a high shear mixer granulator on the structure of agglomerates

m) structure into a tetragonal I41/amd structure. Distinct differences between TEM, XRD, and NPD data indicate the presence of some cation disorder within a rigid close‐packed oxygen framework. The Rietveld refinement of the NPD data suggests a high level of microstrain of 1.2 %. An improvement to the model is achieved by reducing the aluminium content in the unit cell, which is commensurate with the migration of aluminium ions to the surface and some degree of nonstoichiometry in the particle core. Aberration‐corrected TEM imaging and exit wave reconstruction confirm previous evidence for the presence of enhanced surface contrast at {1 1 1} surface facets, which we associate with the presence of excess cation termination. In addition, these {1 1 1} facets are observed to be heavily stepped. These results may have important implications for the thermal stability of metal catalyst nanoparticles on these high‐surface area supports; the migration of aluminium ions to the surface provides clear evidence of why these materials perform so well as catalyst supports.

Influence of contact stiffnesses on the micromechanical characteristics of dense particulate systems subjected to shearing

Tribo‐electrification is an important phenomenon in powder handling, as it could cause hazards and nuisance, such as dust explosion, adhesion to walls and blockage of pipelines leading to powder losses and difficulties in flow control. At present, there are only a few methods available to predict the dynamic charging of bulk powders, and they are not suitable for testing a small quantity of powders or handling highly active powders, for which full isolation would be needed. In this paper, the operation of a simple test device is analysed. Tribo‐electrification of a single spherical bead inside a sealed capsule is induced through a horizontal motion using a shaking device at various frequencies. The single particle contact charge obtained from experiments is incorporated in numerical simulations based on Distinct Element Method (DEM) and is used to predict the transient charge accumulation of an assemblage of beads. In the model, the tribo‐charging of a single bead is related to the contact area of the bea...

Shear deformation of binary mixtures of dry particulate solids

Abstract -High shear mixer granulators are typically found in pharmaceutical and detergent industries, and are capable of reducing processing time and producing agglomerates with high strength and density. Generally, several granulation scaling-up stages are involved before reaching the production level. This is conducted to exert better understanding, control and optimization at the smaller scales before proceeding to the larger scales in terms of geometric, kinematic and/or dynamic similarities. During granulation scaling-up stages, the mechanics of particle interactions and the prevailing level of compressive stresses and strains within the granulator are affected by the variation in hydrodynamics of the granulator as a result of different scales. This in turn affects the final structure of the agglomerates. In this paper we analyze the effect of velocity field of two different scales of high shear mixer granulator (1 and 5 l) on the structure of the evolved agglomerates. The study is based on computer simulation using the discrete element method (DEM). A single agglomerate is generated using DEM computer code and is placed in a bed of primary particles. A velocity field is then superimposed on the surrounding particles. This velocity field corresponds to that obtained experimentally from a separate study using Positron Emission Particle Tracking analysis on 1- and 5-l granulators which were scaled up based on the condition of constant shear stress. The results show that when the velocity profile of the 1-l granulator is used the agglomerate becomes more elongated and it has a smaller packing fraction. Therefore the agglomerate would be weaker.

Distinct element analysis of the effect of temperature on the bulk crushing of α-lactose monohydrate

When characterizing fine particles experimentally, it is a common practice to only measure the normal stiffness between particles and to assume that it is equal to the tangential stiffness. The impact of variations in the stiffness measurements upon the bulk characteristics of particulate systems remains unclear. Using computer simulations, the authors show that the variations in the contact stiffness ratio affect the micromechanical characteristics of nonspherical particulate systems more dominantly than the spherical particulate systems. Hence, attention must be paid to measure both the normal and tangential contact stiffnesses when characterizing nonspherical fine particulates to estimate their assembly characteristics.

Instantaneous Monitoring of Drill Bit Wear and Specific Energy as a Criteria for the Appropriate Time for Pulling Out Worn Bits

Abstract The shear deformation behavior of dry granular materials is of interest in the analysis of flowability, mixing, segregation and degradation. Quite often the particulate systems are mixtures of materials with a wide size distribution. In spite of a large amount of work reported in the literature, the shear behavior of poly-disperse systems has not been widely addressed. In this paper experimental work using an annular shear cell and numerical simulations by the distinct element method (DEM) have been carried out to quantify the normal and shear stress behavior of assemblies made of binary mixtures. The experimental results on mixtures of different sizes of glass beads show a linear relationship between the normal and shear stresses with a slope which depends on the shear rate and particle size ratio. This is an indication of flow in the intermediate regime between the quasi-static and rapid shear flows. The results also indicate a highly non-linear particle displacement distribution across the shear layer. Numerical simulations using the DEM agree qualitatively well with the experimental results for the normal-shear stress behavior.

Particle-Interaction Effects in Turbulent Channel Flow

Abstract Cryogenic milling could reduce the ductility in the milling operations of semi-brittle and relatively ductile pharmaceutical particles. However, to achieve a better application of this technology, it is necessary to establish the relationship between the influence of temperature on the mechanical properties and breakage characteristics of the single particle and the bulk crushing behavior of these types of material. The focus of this paper is on the analysis of bulk crushing behavior of α-lactose monohydrate particles in response to temperature variations, based on single particle mechanical properties and side crushing strength at different temperatures and the use of distinct element analysis. The effect of temperature on the side crushing strength of the particles has been quantified by quasistatic side crushing tests. The experimental results show a significant increase in the strength of the single particles by decreasing the temperature. These results are used in the distinct element analysis to simulate the bulk crushing behavior of pharmaceutical particles as affected by the temperature. The predictions are compared with the experimental results, for which a reasonable agreement is found for the ambient temperature case. There are some differences for the case of −20°C, due to lack of reliable data for Youngs modulus.

Pore Volume Analysis of Gas Shale Samples Using 3-D X-ray Micro Tomography

Current techniques for deciding when to pull out worn bits are based on speculation rather than reliable engineered methods. Two concepts have been previously reported in the literature to incorporate the effects of drilling parameters on forecasting the life of drill bits. Bit tooth flatness and specific energy approaches were used for assessing the bit tooth wear and predicting the rock formation and its properties being drilled. However, drilling shale formations as well as encountering abnormal geologic formations especially unconformities, reduces the reliability of these methods. In this paper, a modified technique based on combined bit dullness and specific energy have been used as trending tools for determining the status of the drill bit even in cases where drill torque data is unavailable. As case studies, currently producing oil wells from southern Iraq are analysed for bit wear. Estimated results of bit wear for each bit run were correlated with the qualitative field bit tooth flatness revealing a successful key index for the suitable time to pull out worn bits. Furthermore, literature values of unconfined compressive strength (UCS) of the drilled formations were compared with the computed mechanical specific energy (MSE) to validate the obtained results. Good agreement was observed making the study encouraging. The analysis is promising for evaluating drill bit selection and predicting the type of formation being drilled.

Reynolds number effects on particle agglomeration in turbulent channel flow

Large eddy simulation and a discrete element method are applied to study the flow, particle dispersion and agglomeration in a horizontal channel. The particle-particle interaction model is based on the Hertz-Mindlin approach with Johnson-Kendall-Roberts cohesion to allow the simulation of Van der Waals forces in a dry air flow. The influence of different particle surface energies on agglomeration, and the impact of fluid turbulence, are investigated. The agglomeration rate is found to be strongly influenced by the particle surface energy, with most of the particle-particle interactions taking place at locations close to the channel walls, aided by the higher concentration of particles in these regions.