The Mediterranean biocoenosis of infralittoral pebbles has been poorly studied and very little information is available on the physical characteristics of pebble beds, on the diversity of the associated assemblages, on the spatial and temporal variation in assemblage structure, or on interactions between the physical and biotic components. The present study was therefore carried out to characterise pebble-bed assemblages as a first step towards understanding the ecological dynamics of these habitats. Preliminary surveys were made along the low-lying coasts of the Maltese Islands to map the occurrence of pebble-bed habitats. Fifteen locations with pebble coverage >25 m² were chosen for study and benthic sampling was undertaken between July–September 2011; water samples were also collected on a monthly basis. Five shallow sites were sampled for biota again at six-month intervals until April 2013. The pebble beds were characterised in terms of environmental parameters and biotic composition. A total of 62,742 individuals belonging to 360 macrofaunal taxa were recorded (total sampling area: 16 m²). Polychaetes, crustaceans and molluscs were the most common faunal groups. The recorded species included the endemic gastropod Gibbula nivosa, and the first central Mediterranean records of three gobiid species. Three distinct pebble-bed types were characterised based on physical and biological features: shallow beds occurring in rocky coves, beds found within creeks or seagrass meadows, and beds located in harbour environments; amendments to internationally used benthic habitat classification schemes have been proposed, since only a single category of pebble-bed habitats is currently recognised in these. A significant seasonal reduction in species richness and abundance was recorded from shallow sites, related to the higher level of disturbance occurring during winter storms. Analysis of diversity patterns in harbour sites indicated that a high richness per site and between-site variation in species composition led to the observed high diversity. Site richness was associated with fine-scale structural complexity, while environmental characteristics were correlated with variation in assemblage structure over a broad range of spatial scales. These findings suggest that pebble beds have a higher conservation value than generally thought. The biologically derived habitat classification scheme and knowledge on assemblage-environment relationships derived from the present work will be useful to inform and guide management decisions concerning these pebble-bed habitats.

Gas fluidised beds are important components in many process industries, e.g. coal combustors and granulators, but not much is known about the movement of the solids. Positron Emission Particle Tracking (PEPT) enables the movement of a single, radioactive tracer particle to be followed rapidly and faithfully. Experiments were carried out in columns sized between 70 and 240mm diameter, operating in the bubbling regime at ambient process conditions using particles of group B and D (Geldart Classification). Particle motion was tracked and the data applied to models for particle movement at the gas distributor as well as close to other surfaces and to models for particle circulation in beds of cohesive particles. In the light of these data, models for particle and bubble interaction, particle circulation, segregation, attrition, erosion, heat transfer and fluidised bed scale-up rules were reassessed. Particle motion is directly caused by bubble motion, and their velocities were found to be equal for particles travelling in a bubble. PEPT enables particle circulation to be measured, giving a more accurate correlation for future predictions. Particle motion follows the scale-up rules based on similarities of the bubble motion in the bed. A new group of parameters was identified controlling the amount ofattrition in fluidised beds and a new model to predict attrition is proposed.

No description available.

When a disordered packed bed, or any heterogeneous media is studied using computational fluid dynamics, the tortuous task of generating a domain and creating a workable mesh presents a challenging issue to Engineers and Scientists. In this Thesis these challenges are addressed in the form of three studies in which both traditional and novel techniques are used to generate packed beds of spheres and cylinders for analysis using computational fluid dynamics, more specifically, the finite volume method. The first study uses a Monte-Carlo method to generate random particle locations for use with a traditional CADbased meshing approach. Computational studies are performed and compared in detail with experimental equivalent beds. In the second study, where there is a need for actual, physical beds to be studied, magnetic-resonance-imaging is used coupled with a novel approach known as image based meshing. In parallel experimental studies are performed on the experimental bed and compared with computational data. In the third study, to overcome fidelity issues with the previous approaches, a physical packed bed is manufactured which is 100% geometrically faithful to its computational counterpart to provide a direct comparison. All three computational studies have shown promising results in comparison with the experimental data described in this Thesis, with the data of Reichelt (1972) and the semi-empirical correlation of Eisfeld & Schnitzlein (2001). All experiments and computational models were carried out by the author unless otherwise stated.

The main objective of this research was to model the airflow paths through grain bulks and predict the resistance to airflow. The discrete element method (DEM) was used to simulate the pore structures of grain bulks. A commercial software package PFC3D (Particle Flow Code in Three Dimension) was used to develop the DEM model. In the model, soybeans kernels were considered as spherical particles. Based on simulated positions (coordinates) and radii of individual particles, the characteristics of airflow paths (path width, tortuosity, turning angles, etc.) in the vertical and horizontal directions of the grain bed were calculated and compared. The discrete element method was also used to simulate particle packing in porous beds subjected to vertical vibration. Based on the simulated spatial arrangement of particles, the effect of vibration on critical pore structure parameters (porosity, tortuosity, pore throat width) was quantified. A pore-scale flow branching model was developed to predict the resistance to airflow through the grain bulks. Delaunay tessellation was also used to develop a pore network model to predict airflow resistance. Experiments were conducted to measure the resistance to airflow to validate the models. It was found that the discrete element models developed using PFC3D was capable of predicting the pore structures of grain bulks, which provided a base for geometrically constructing airflow paths through the pore space between particles. The tortuosity for the widest and narrowest airflow paths predicted based on the discrete element model was in good agreement with the experimental data reported in the literature. Both pore-scale models (branched path and network) proposed in this study for predicting airflow resistance (pressure drop) through grain bulks appeared promising. The predicted pressure drop by the branched path model was slightly (<12%) lower than the experimental value, but almost identical to that recommended by ASABE Standard. The predicted pressure drop by the network model was also lower than the measured value (2.20 vs. 2.44 Pa), but very close to that recommended by ASABE Standard (2.20 vs. 2.28Pa). / February 2017

Pas de résumé / Fluidized beds are a particular hydrodynamic configuration in which a pack (either dense or loose) of particles laid inside a container is re-suspended as a result of an upward oriented imposed flow at the bottom of the pack. This kind of system is widely used in the chemical engineering industry where catalytic cracking or polymerization processes involve chemical reactions between the catalyst particles and the surrounding fluid and fluidizing the bed is admittedly beneficial to the efficiency of the process. Due to the wide range of spatial scales and complex features of solid/solid and solid/fluid interactions in a dense fluidized bed, the system can be studied at different length scales, namely micro, meso and macro. In this work we focus on micro/meso simulations of fluidized beds. The workflow we use is based on home made high-fidelity numerical tools: GRAINS3D (Pow. Tech., 224:374-389, 2012) for granular dynamics of convex particles and PeliGRIFF (Parallel Efficient LIbrary for GRains In Fluid Flows, Comp. Fluids, 38(8):1608-1628,2009) for reactive fluid/solid flows. The objectives of our micro/meso simulations of such systems are two-fold: (i) to understand the multi-scale features of the system from a hydrodynamic standpoint and (ii) to analyze the performance of our meso-scale numerical model and to improve it accordingly. To this end, we first perform Particle Resolved Simulations (PRS) of liquid/solid and gas/solid fluidization of a 2000 particle system. The accuracy of the numerical results is examined by assessing the space convergence of the computed solution in order to guarantee that our PRS results can be reliably considered as a reference solution for this problem. The computational challenge for our PRS is a combination of a fine mesh to properly resolve all flow length scales to a long enough physical simulation time in order to extract time converged statistics. For that task, High Performance Computing and highly parallel codes as GRAINS3D/PeliGRIFF are extremely helpful. Second, we carry out a detailed cross-comparison of PRS results with those of locally averaged Euler- Lagrange simulations. Results show an acceptable agreement between the micro- and meso-scale predictions on the integral measures as pressure drop, bed height, etc. However, particles fluctuations are remarkably underpredicted by the meso-scale model, especially in the direction transverse to the main flow. We explore different directions in the improvement of the meso-scale model, such as (a) improving the inter-phase coupling scheme and (b) introducing a stochastic formulation for the drag law derived from the PRS results. We show that both improvements (a) and (b) are required to yield a satisfactory match of meso-scale results with PRS results. The new stochastic drag law, which incorporates information on the first and second-order moments of the PRS results, shows promises to recover the appropriate level of particles fluctuations. It now deserves to be validated on a wider range of flow regimes.

Understanding the controls on fluid migration in reservoir rocks is becoming evermore important within the petroleum industry as significant hydrocarbon discoveries become less frequent and more emphasis is placed on enhanced oil recovery methods. To fully understand the factors controlling fluid migration in the subsurface, pore scale information is necessary. In this study, synchrotron-based X-ray computed microtomography (CMT) is being utilized to extract physically realistic images of carbonate rock cores for the evaluation of porosity and mineralogy in the Mississippian Midale beds of the Weyburn Oilfield in southeastern Saskatchewan. Non-destructive in-situ imaging by CMT is unique as it provides a detailed and novel approach for the description of pore space geometry, while preserving connectivity and spatial variation of pore-body and pore-throat sizes. Here, three-dimensional micron to sub-micron (0.3ìm-100ìm) resolution of CMT is coupled with, and compared against, conventional laboratory-based methods (liquid and gas permeametry, mercury injection porosimetry, electrical resistivity, backscattered electron (BSE) from electron probe micro-analysis (EPMA) and transmitted light microscopy). Petrophysical and mineralogical information obtained from both CMT and conventional methods will have direct implications for understanding the petrophysical mechanisms that control fluid movement in the subsurface of the Weyburn Oilfield.<p>At Weyburn, CO2 gas is being injected into producing horizons to enhance oil recovery and permanently sequester CO2 gas. Fundamental questions exist regarding: (1) The significance of pore geometry and connectivity to the movement of CO2 and other fluids in the subsurface, (2) the nature of the interactions between CO¬2 and pore lining minerals and their impact on petrophysical properties, and (3) the distribution and mineralogy of finely disseminated silicate and carbonate minerals adjacent to pore spaces as interaction among these phases and CO2 may result in permanent sequestration of CO2. <p>The two producing horizons within the Weyburn Reservoir, the Midale Marly and Midale Vuggy units, have variable porosities and permeabilities. Porosity in the Marly unit ranges from 16% to 38% while permeability ranges from 1mD to greater than 150 mD across the field. For the Vuggy unit, porosity ranges from 8% to 21% with permeability ranging from 0.3mD to 500mD. Using CMT, pore space is critically examined to highlight the controlling factors on permeability. Digital processing of CMT data indicates that pore space in the Marly unit is dominated by intercrystalline pores having diameters of approximately 4 ìm. From here, it is noted that the pore-throat radii are approximately ½ the radii of the pore-bodies, having profound implications to current oil recovery methods. Tortuosity values from CMT are also observed to have similar values in three orthogonal directions indicating an isotropic pore space distribution within the Marly unit. Alternatively, the Vuggy unit is found to possess greater pore-body and pore-throat sizes that are heterogeneous in distribution. Based on this, permeability in the Vuggy unit is strongly dependant on pore-length scales that vary drastically between localities.

Understanding the controls on fluid migration in reservoir rocks is becoming evermore important within the petroleum industry as significant hydrocarbon discoveries become less frequent and more emphasis is placed on enhanced oil recovery methods. To fully understand the factors controlling fluid migration in the subsurface, pore scale information is necessary. In this study, synchrotron-based X-ray computed microtomography (CMT) is being utilized to extract physically realistic images of carbonate rock cores for the evaluation of porosity and mineralogy in the Mississippian Midale beds of the Weyburn Oilfield in southeastern Saskatchewan. Non-destructive in-situ imaging by CMT is unique as it provides a detailed and novel approach for the description of pore space geometry, while preserving connectivity and spatial variation of pore-body and pore-throat sizes. Here, three-dimensional micron to sub-micron (0.3ìm-100ìm) resolution of CMT is coupled with, and compared against, conventional laboratory-based methods (liquid and gas permeametry, mercury injection porosimetry, electrical resistivity, backscattered electron (BSE) from electron probe micro-analysis (EPMA) and transmitted light microscopy). Petrophysical and mineralogical information obtained from both CMT and conventional methods will have direct implications for understanding the petrophysical mechanisms that control fluid movement in the subsurface of the Weyburn Oilfield.<p>At Weyburn, CO2 gas is being injected into producing horizons to enhance oil recovery and permanently sequester CO2 gas. Fundamental questions exist regarding: (1) The significance of pore geometry and connectivity to the movement of CO2 and other fluids in the subsurface, (2) the nature of the interactions between CO¬2 and pore lining minerals and their impact on petrophysical properties, and (3) the distribution and mineralogy of finely disseminated silicate and carbonate minerals adjacent to pore spaces as interaction among these phases and CO2 may result in permanent sequestration of CO2. <p>The two producing horizons within the Weyburn Reservoir, the Midale Marly and Midale Vuggy units, have variable porosities and permeabilities. Porosity in the Marly unit ranges from 16% to 38% while permeability ranges from 1mD to greater than 150 mD across the field. For the Vuggy unit, porosity ranges from 8% to 21% with permeability ranging from 0.3mD to 500mD. Using CMT, pore space is critically examined to highlight the controlling factors on permeability. Digital processing of CMT data indicates that pore space in the Marly unit is dominated by intercrystalline pores having diameters of approximately 4 ìm. From here, it is noted that the pore-throat radii are approximately ½ the radii of the pore-bodies, having profound implications to current oil recovery methods. Tortuosity values from CMT are also observed to have similar values in three orthogonal directions indicating an isotropic pore space distribution within the Marly unit. Alternatively, the Vuggy unit is found to possess greater pore-body and pore-throat sizes that are heterogeneous in distribution. Based on this, permeability in the Vuggy unit is strongly dependant on pore-length scales that vary drastically between localities.

Thesis (M.S.)--Oregon State University. / Includes bibliographical references (leaves 62-65). Also available on the World Wide Web.

The cooling preceding the beginning of North American continental glaciation is beautifully represented by the thick fluvial and lacustrine sequences of the Pliocene Glenns Ferry Formation at the Hagerman Fossil Beds National Monument (HAFO), Idaho. This time interval is commonly studied because it contains the elevated global temperatures predicted to result from continued anthropogenic warming. The fossil mammals at HAFO were examined to see the effects of climate change on past mammalian assemblages. The nature of the fossiliferous localities at HAFO was documented to establish which localities could be considered in situ. Additionally, the structural architecture of the beds was mapped to establish an idealized stratigraphic datum to which localities were tied. This facilitated temporal comparison of the widespread localities at HAFO. Second, a high-resolution record of climate change was created using global climate models to predict which oceanic areas varied in temperature in concert with HAFO during the middle Pliocene. Data from deep-sea cores from those oceanic areas were combined to create a proxy temperature pattern; such a detailed record from terrestrial data in the Glenns Ferry Formation is not currently possible. Selected mammalian groups, carnivorans, insectivorans, and leporids, were examined in light of the established climatic patterns. The cooling through the lower portion of the Glenns Ferry Formation corresponds to variation in the morphology of individual species, the relative abundance of species, and the species-level diversity of mammalian groups. There is a return to warm temperatures near the top of the section at HAFO, and the mammals returned to the conditions exhibited before the cool-temperature extreme. This faunal resilience, however, occurred over hundreds of thousands of years. The final paleoecologic approach established correlations between the species diversity of groups of modern mammals and modern climatic values. Many modern groups were found to be highly-significantly correlated to climate, but when the established predictive equations were applied to HAFO, the results were variable. Estimates of annual precipitation varied widely, depending on the taxonomic group, and also deviated from precipitation estimates from sedimentology. Temperature patterns were more consistent with each other and with the pattern of the deep-sea core proxy. / text