No / Two numerical particle models, the Smoothed Particle Hydrodynamics (SPH) and Moving Particle Semi-implicit (MPS) methods, coupled with a sub-particle scale (SPS) turbulence model, are presented to simulate free surface flows. Both SPH and MPS methods have the advantages in that the governing Navier¿Stokes equations are solved by Lagrangian approach and no grid is needed in the computation. Thus the free surface can be easily and accurately tracked by particles without numerical diffusion. In this paper different particle interaction models for SPH and MPS methods are summarized and compared. The robustness of two models is validated through experimental data of a dam-break flow. In addition, a series of numerical runs are carried out to investigate the order of convergence of the models with regard to the time step and particle spacing. Finally the efficiency of the incorporated SPS model is further demonstrated by the computed turbulence patterns from a breaking wave. It is shown that both SPH and MPS models provide a useful tool for simulating free surface flows

The aim of this thesis is three-fold: i) to investigate the performance of both the Eulerian-Lagrangian model and the Eulerian-Eulerian model to simulate the turbulent gas-particle flow; ii) to investigate the indoor airflows and contaminant particle flows using the Eulerian-Lagrangian model; iii) to develop and validate particle-wall collision models and a wall roughness model for the Eulerian-Lagrangian model and to utilize these models to investigate the effects of wall roughness on the particle flows. Firstly, the Eulerian-Lagrangian model in the software package FLUENT (FLUENT Inc.) and the Eulerian-Eulerian model in an in-house research code were employed to simulate the gas-particle flows. The validation against the measurement for two-phase flow over backward facing step and in a 90-degree bend revealed that both CFD approaches provide reasonably good prediction for both the gas and particle phases. Then, the Eulerian-Lagrangian model was employed to investigate the indoor airflows and contaminant particle concentration in two geometrically different rooms. For the first room configuration, the performances of three turbulence models for simulating indoor airflow were evaluated and validated against the measured air phase velocity data. All the three turbulence models provided good prediction of the air phase velocity, while the Large Eddy Simulation (LES) model base on the Renormalization Group theory (RNG) provided the best agreement with the measurements. As well, the RNG LES model is able to provide the instantaneous air velocity and turbulence that are required for the evaluation and design of the ventilation system. In the other two-zone ventilated room configuration, contaminant particle concentration decay within the room was simulated and validated against the experimental data using the RNG LES model together with the Lagrangian model. The numerical results revealed that the particle-wall coll ision model has a considerable effect on the particle concentration prediction in the room. This research culminates with the development and implementation of particle-wall collision models and a stochastic wall roughness model in the Eulerian-Lagrangian model. This Eulerian-Lagrangian model was therefore used to simulate the gas-particle flow over an in-line tube bank. The numerical predictions showed that the wall roughness has a considerable effect by altering the rebounding behaviours of the large particles and consequently affecting the particles motion downstream along the in-line tube bank and particle impact frequency on the tubes. Also, the results demonstrated that for the large particles the particle phase velocity fluctuations are not influenced by the gas-phase fluctuations, but are predominantly determined by the particle-wall collision. For small particles, the influence of particle-wall collisions on the particle fluctuations can be neglected. Then, the effects of wall roughness on the gas-particle flow in a two-dimensional 90-degree bend were investigated. It was found that the wa ll roughness considerably altered the rebounding behaviours of particles by significantly reducing the 'particle free zone' and smoothing the particle number density profiles. The particle mean velocities were reduced and the particle fluctuating velocities were increased when taking into consideration the wall roughness, since the wall roughness produced greater randomness in the particle rebound velocities and trajectories.

Resuspension is an important source of particles in the indoor environment. A variable that may have a significant impact on the fraction of particles removed from indoor surfaces is the type of particle deposit. Particles may be deposited in either a monolayer, where there is minimal particle-to-particle contact, or a multilayer, where there is substantial particle-to-particle contact and interaction. This paper provides a review of theoretical and experimental studies on particle resuspension from monolayer and multilayer particle deposits. In addition, an experimental methodology was developed to determine resuspension from the two types of deposits on indoor surfaces. Seeded samples were exposed to controlled flow conditions in a micro-scale wind tunnel and were analyzed with fluorescence stereomicroscopy. Resuspension was found to occur at significantly lower velocities for multilayer deposits compared to monolayer deposits. / text

Formation damage is a common problem in petroleum reservoirs and happens in different stages of reservoir development from drilling to production. The causes of formation damage include particle invasion, formation fines migration, chemical precipitation, and pore deformation or collapse. Formation damage adversely affects productivity of wells by reducing the permeability of near wellbore region. Furthermore, formation damage also affects well logging results. Therefore, understanding the mechanism of formation damage is vital to predict the extent and severity of formation damage and to control it. This thesis is focused on the study of formation damage caused by external particle invasion. A simplified numerical method based on a commercial code PFC (Particle Flow Code) is proposed to simulate the particle invasion process. The fluid-particle interaction is simplified as hydrodynamic drag forces acted on particles by fluids; the particle-grain interaction is modeled as two rigid balls on contact. Furthermore, an pore network flow model is developed in this study to estimate permeability of damaged formations, which contain two well-separated particle sizes. The effects of the particle size and the initial formation porosity on formation damage are studied in detail. Our study shows that big particles tend to occupy the formation face, while small particles invade deep into the formation. Moreover, particles which are smaller than pore throats (entrances) impair permeability more than those bigger than pore throats. Our study also indicates that a higher initial formation porosity results in more particle invasion and permeability impairment. It is suggested that, in order to reduce formation damage, mud particle size distributions should be carefully selected according to given formation properties. Although our model has some limitations, it may serve as a tool to predict formation damage according to given parameters, and to understand the mechanism of formation damage from a micro-scopic point of view. / text

No description available.

The addition of coarse particles to a flocculating fine particle slurry increases the Bingham yield stress of the resulting mixture, which can drastically alter the laminar-to-turbulent transition velocity. The objective of this study is to quantify the effect of coarse particle size and volume concentration on mixture rheology. Fine particle (kaolin) mixtures of 10% to 22% (by volume) were prepared, to which sand particles were added to provide a coarse solid concentration of 5% to 20% (by volume). Sand particles of two different sizes – 90 and 190 microns – were added and these kaolin-sand-water mixtures tested with a concentric cylinder viscometer. At higher total solids concentrations, the Bingham yield stress of the bimodal mixture can increase by as much as 80% over that of a kaolin-only slurry. Coarse particle diameter had little effect. This study demonstrates that the use of existing correlations should be eschewed. System-specific high-quality measurements are necessary. / Chemical Engineering

abstract: This dissertation describes a novel, low cost strategy of using particle streak (track) images for accurate micro-channel velocity field mapping. It is shown that 2-dimensional, 2-component fields can be efficiently obtained using the spatial variation of particle track lengths in micro-channels. The velocity field is a critical performance feature of many microfluidic devices. Since it is often the case that un-modeled micro-scale physics frustrates principled design methodologies, particle based velocity field estimation is an essential design and validation tool. Current technologies that achieve this goal use particle constellation correlation strategies and rely heavily on costly, high-speed imaging hardware. The proposed image/ video processing based method achieves comparable accuracy for fraction of the cost. In the context of micro-channel velocimetry, the usability of particle streaks has been poorly studied so far. Their use has remained restricted mostly to bulk flow measurements and occasional ad-hoc uses in microfluidics. A second look at the usability of particle streak lengths in this work reveals that they can be efficiently used, after approximately 15 years from their first use for micro-channel velocimetry. Particle tracks in steady, smooth microfluidic flows is mathematically modeled and a framework for using experimentally observed particle track lengths for local velocity field estimation is introduced here, followed by algorithm implementation and quantitative verification. Further, experimental considerations and image processing techniques that can facilitate the proposed methods are also discussed in this dissertation. Unavailability of benchmarked particle track image data motivated the implementation of a simulation framework with the capability to generate exposure time controlled particle track image sequence for velocity vector fields. This dissertation also describes this work and shows that arbitrary velocity fields designed in computational fluid dynamics software tools can be used to obtain such images. Apart from aiding gold-standard data generation, such images would find use for quick microfluidic flow field visualization and help improve device designs. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011

Particle breakage can be significant in stirred vessels such as crystallizers. During crystallization, particle breakage can occur due to particle contact with other particles, the impeller, the suspension fluid, and/or the vessel. Such breakage produces fines and can cause filter plugging downstream. Although research has been conducted with respect to particle breakage, a comprehensive study is still needed to quantify the breakage occurring in stirred vessels. The overall goal of this research is to model the particle breakage occurring in a stirred vessel by analyzing the particle size and shape distributions that result from breakage. Breakage experiments are based on collision influences that affect the two dominant collisions types, crystal-to-crystal and crystal-to-impeller collisions. Results showed that the quantity of fines produced are affected by the solids concentration or magma density and suspension fluid utilized. Additionally, aqueous saturated solutions produced particle size distributions that differ from those obtained using a nonsolvent. Similar particle size distributions for two different materials (NaCl and KCl) are achieved in the same nonsolvent (acetonitrile) by adjusting the agitation rate using the Zwietering correlation to account for property differences; moreover, the same agitation rate adjustment produced similar distributions for KCl in acetone and acetonitrile which were both nonsolvents. However, modifications to the Zwietering correlation, such as changing the significance of the initial particle size, are proposed before this method of adjustment is deemed accurate. Number-based population modeling of particle breakage is achieved within 1-5% error for NaCl at each agitation rate investigated. Breakage modeling using a discretized population balance equation with Austin's equation for attrition and the power law form of the product function for fragmentation is a viable approach; however, more work is needed to increase the accuracy of this model.

No description available.

This work evaluates the relative significance of forces determining the motion of a pulverized coal particle under conditions representative of a pressurized oxy-coal combustor. The gravity force and surface forces of drag, fluid stress, added mass, and Basset history are discussed and appropriate forms of these force equations are chosen, with a consideration of spherical and non-spherical drag and the Basset history kernel. Studies from the literature that emphasize specific forces are used to validate the implementation of the force equations and correlations. Modeling is based on time-averaged, one-dimensional motion of a single non-reacting particle along the centerline of a round, turbulent jet. The numerical methodology employed for solving the particle equation of motion is described in detail, and simulated particle motion is compared to experimental and high-fidelity simulations from the literature. Comparisons show the numerical methodology performs adequately relative to higher fidelity simulations and experimental test cases for one-dimensional, time-invariant conditions. To assess the effect of pressure on particle forces and motion under different conditions, simulation cases are run for particle diameters of 20 μm, 50 μm, 125 μm, gas temperatures of 300 K and 1500 K, and gas pressures of 1.01325 bar, 2 bar, 5 bar, 10 bar, 20 bar, 40 bar. Simulations are conducted over a 0.75-m length in a simplified environment representative of the pressurized oxy-coal (POC) combustor at Brigham Young University. Results show that all surface forces examined can be locally significant at high gas pressures when particle and gas velocity differences, i.e., particle Reynolds numbers, are greatest. The following trends are found for the behavior of surface forces in simplified, POC combustor simulations: 1) The quasi-steady drag force is always significant, though it's relative contribution to particle motion decreases as particles traverse regions with significant fluid velocity gradients or significant values for the substantial derivative of fluid velocity. Furthermore, quasi-steady drag is the only surface force that is significant throughout the entirety of a particle's trajectory. The relative contribution of the drag force decreases with increasing gas pressure. 2) The impact of the fluid stress force on particle motion increases with increasing gas pressure and particle size. The fluid stress force can be locally important for all of the particles sizes when at a gas temperature of 300 K and elevated pressure, as particles traverse regions with significant substantial derivatives of fluid velocity. The local impact of the fluid stress force is largely negligible at 1500 K, except for the case of the largest particle at the greatest pressure. 3) The behavior of the added mass force largely mirrors that of the fluid stress force, though the added mass force is generally of lesser magnitude. Therefore, the added mass force can be locally important for all of the particles sizes when at a gas temperature of 300 K and elevated pressure, as particles traverse regions with significant substantial derivatives of fluid velocity. The added mass force is generally the least significant of the analyzed surface forces. 4) The Basset history force is locally significant for all cases where the particles are traversing regions with significant fluid velocity gradients. The impact of the Basset history force on particle motion increases with increasing gas pressure and particle size, while decreasing as gas temperature increases.