Dual PE-CVD Circulating Fluidized Bed Reactor

The endodermal location of 'germinal plasm'-bearing cells (GPBCs) and the ultrastructure of the 'germinal plasm' were studied in Xenopus laevis embryos at gastrula, neurula, tailbud and younger tadpole stages. Primordial germ cells (PGCs) of feeding tadpoles were also observed ultrastructurally. GPBCs were found in the inner endoderm and in the yolk plug region at the late gastrula stage, in the middle and in the dorsal part of the endoderm cell mass at the late neurula and late tailbud stages, respectively. At the younger tadpole stage they were observed in the uppermost dorsal part of the endoderm. Germinal granules were always present in GPBCs at all stages examined but were not found in PGCs of feeding tadpoles. Irregularly shaped-stringlike bodies (ISBs) which seemed to have changed from germinal granules were first noticed in GPBCs at the late neurula stage, and were still present in PGCs of tadpoles, while 'granular materials' were not seen in GPBCs until the feeding tadpole stages. These facts and ultrastructural similarities shared by these organelles lead us to conclude that the change of the germinal granule through ISB, to the 'granular material' takes place during the differentiation of GPBCs into PGCs.

Chemical looping combustion of Victorian brown coal using Fe-based oxygen carriers

Growth of polycrystalline silicon from fluidized bed reactors (FBR) produces two general types of silicon products: granular material (diameters on the order of mm) and homogeneously nucleated material often called nanopowder (diameters in the range 10–100 nm). Nanopowder particles tend to be amorphous and have a spherical morphology with an average particle diameter of ~80 nm. Granular material is generally spherical, highly twinned, polycrystalline with crystallite sizes that can reach 200 nm, and includes regions of porosity. The porosity is ~1–4 volume percent, and only the smallest pores exhibit evidence of amorphous regions along the pore surface. The amount of nanopowder that agglomerates on the granular material has been identified using transmission electron microscopy, but agglomeration plays only a minor role in the overall growth process. Therefore, it is proposed that the primary mechanism for granular formation in commercial FBR is chemical vapor deposition, and the pores are associated with nanopowder agglomeration and incomplete sintering.

On energy transfer and dissipation of intruder impacting granular materials based on discrete element simulations

Granular materials are extensively used throughout many industries. In countries like Australia and South Africa, national economies are critically dependent on the agricultural and mining industries, and it is important to understand bulk material behaviour in order to handle these materials properly. There are many diverse approaches to modelling granular materials. In this thesis, the Coulomb-Mohr continuum mechanical theory of granular materials is utilised, and some exact analytical solutions are presented for both stress and velocity fields. These solutions are formally valid provided sin φ = 1, where φ is the angle of internal friction, and they provide limiting solutions for so called highly frictional granular materials, for which sin φ ≈ 1. The solutions so obtained are exploited for three real industrial granular problems, namely gravity flow from converging hoppers, the stress distribution in stockpiles and finally, the stress distribution within rat-holes. The flow of granular materials, in the presence of gravity, through a converging hopper is an important problem that occurs in many industrial processes. Here, for highly frictional granular materials for both wedge and conical hopper flows, exact analytical solutions are obtained to determine the stress and velocity fields within the neighborhood of the hopper outlet. For the same problem, these exact solutions are exploited as the leading order terms in a regular perturbation series, where the correction terms are of order 1− sin φ. In this way, approximate analytical solutions are obtained that can be used to describe the behaviour of more realistic granular materials. The practice of storing granular materials in stockpiles occurs throughout the ii world in many industrial situations. In this thesis, exact solutions for highly frictional granular materials are used for the determination of the stress distributions within two-dimensional and axially symmetric stockpiles. Stockpile profiles considered here include the standard wedge and cone, as well as two-dimensional parabolic and axially symmetric cubic curved shaped stockpiles. We emphasise that curved stockpiles have not previously been considered in the literature. Our model assumes that the stockpile is composed of two regions, namely an inner rigid region and an outer yield region. The exact solution applies in the outer yield region, which is then extended continuously into the inner rigid region. A rat-hole is the general term used to describe those stable cavities, which frequently occur in storage hoppers and stockpiles, whose formation prevents further material falling through the outlet. In this thesis, we present exact solutions for both two-dimensional and axially symmetric rat-holes, where it is assumed that the highly frictional granular material has flowed through a central outlet, until the point is reached when there is no further flow of material. The remaining material is assumed to be in limiting equilibrium, that is static but on the point of yield. In both two dimensions and axial symmetry, two types of rat-holes are studied. The first type has a sloping upper surface of infinite extent, where the material is resting on a sloping rigid base containing an infinitesimal central outlet. The second type has a curved upper surface, where the material is resting between vertical walls and a horizontal rigid plane containing an infinitesimal central outlet. Again, we emphasise that neither of these rat-hole problems have previously been investigated in the literature.

Electrothermal purification is an effective method for achieving over 99.9 pct purity for graphite particles with minimal environmental impact. However, the lack of a suitable heat and electric resistivity model has hindered the scaling up of electrically heated fluidized bed (EHFB) reactors for graphite purification. In this study, three commercial natural graphite flake populations were tested in a bench-scale fluidized bed reactor at temperatures of up to 1000 °C. The experiments varied key parameters, including the graphite particle size, particle bed temperature, fluidization index, and electrode depth within the particle bed. Controlling the fluidized bed reactor at high temperatures requires an understanding of bed resistivity and how current flows throughout the EHFB system. The results show that fluidized bed resistivity decreases with temperature, with a diminished effect at higher temperatures. Smaller particles exhibit a higher resistance, likely due to a larger number of contact points required to pass current between the electrodes. In this study, a Finite Difference Method (FDM) model was developed using Visual Basic for Applications (VBA) in Excel®. Additionally, a Finite Element Method (FEM) model was created using COMSOL Multiphysics®. The FDM model assumes the current flows only radially, whereas the FEM model accounts for both radial and vertical current flow. The FDM model was validated against experimental data. Additionally, the FDM model was verified through a comparison with the FEM model. The FDM model showed good agreement with experimental resistance data and moderate agreement with power consumption, while the FEM model provided more accurate predictions by accounting for a detailed geometry and heat loss mechanisms. Achieving a uniform temperature distribution within the fluidized bed is influenced by the electrode’s contact area. Deeper immersion of the electrode enhances thermal uniformity and provides results that more closely match experimental observations.

In-situ nitrogen doping in carbon nanotubes using a fluidized bed reactor and hydrogen storage behavior of the doped nanotubes

Multiscale modeling and characterization of coupled damage-healing-plasticity for granular materials in concurrent computational homogenization approach

Skins with asymmetric kirigami scales and soft spikes are integrated to the surface of a base self‐burrowing robot, which consists of a soft one‐segment extending actuator. Friction anisotropy is observed at the interfaces between the burrowing robots and different granular materials. Its effects on the pulling resistance and burrowing characteristics are studied. The results demonstrate that the development of friction and friction anisotropy is affected by the characteristics of the granular material, the asymmetric skins, and the relative size of the asymmetric features to the granular particles. Robots with scales or spikes aligned along the upward direction burrow faster than those aligned against the upward direction, especially in relatively coarser granular materials. Particle image velocimetry analysis on the particle displacement fields around the actuator reveals the complexity of dry granular material interactions with soft robots, implying that aligned scales or spikes can impact the distribution of friction preferentially, opening up many possibilities for thoughtful material and geometry‐based manipulation of friction in the design and optimization of future soft burrowing robots for more versatile locomotion capabilities.

Granular material under the action of gravity flows down an incline tube or plane. This paper presents a phenomenon in which a granular material climbs along a vertically vibrating tube that is partially inserted in a granular silo. In this scenario the final climbing height increases with increasing vibration strength and tube insertion depth. However, the climbing velocity of the granular material does not monotonically increase with the climbing height. A transition height, at which the granular material has the highest climbing velocity, also exists. When the tube vibrates, the force between the tube and the particles varies periodically, thus inducing the directional climbing of particles. By analyzing the forces on the particles, we present a model that is qualitatively consistent with the experimental results.

Modeling of autothermal reforming of methane in a fluidized bed reactor with perovskite membranes

99/00352 Modeling of gasification behavior in freeboard of fluidized bed gasifier

Advancements of the Fluidized Bed Fenton (FBF) Technology for wastewater treatment: Mechanism, mass and heat transfer

This paper deals with the mechanical behaviour, especially the permanent deformation and resilient deformation of an unbound granular material (UGM) from Bréfauchet quarry which is used as base layer material in low traffic pavements for full-scale tests at IFSTTAR in France. Medium-scale repeated load triaxial tests (RLTT) are carried out at different water contents and the results show that both permanent and resilient deformations increase with water content. Besides, two techniques of fixing the sensors in materials with large particles for RLTTs are proposed and compared with each other. The results suggest that the tube method is more suitable for the UGM for an accurate measurement and a good adaptability is obtained during the RLTT. Based on the test results of UGM Bréfauchet, the modelling work is performed with improved models used previously for a sandy material. It appears that both the permanent and resilient behaviours of different unbound granular materials can be well captured by the proposed equations considering the effects of water content and anisotropy. This study is helpful to understand the evolution of permanent and resilient deformation in different granular layers, especially for the base layer, in low traffic pavements. The verified models can be used for other similar granular materials and this will lead to reducing the number of tests required to predict the deformation behaviour of granular materials.

Local velocity gradients on a solid spherical surface have been studied in a bubble column and in two‐ and three‐phase fluidized beds, in order to clarify the influence of gas flow. The electrochemical method, measuring apparent local mass transfer coefficients, was verified and used to obtain the local velocity gradients, shear stresses and total frictional forces. The observed mass transfer rate was independent of liquid velocity, owing to a non‐changing flow structure around the particles and not to averaging opposing effects. The identity in flow structure also held for three‐phase fluidized beds up to a superficial gas velocity of 5 cm s−1. The dramatic increase in velocity gradient on gas introduction was not a result of decreased homogenous density, but was caused by a change in the turbulent structure around a particle, leaving a larger portion of the total drag as frictional drag, thus improving the mass transfer characteristics of the bed. Use of velocity gradient measurements, including span of fluctuations and exposure time, to predict biomass growth and mechanical degradation in a reactor is also discussed.