<p>Steel refining via ladle treatment is critical to final product quality in the steel manufacturing process. The process of ladle refining serves to assist in the removal of non-metallic inclusions, which can impact steel product fatigue strength, impact toughness, and corrosion resistance. While the steelmaking industry has in place best practices for the process, it remains costly to performing trial and error testing on the ladle. In addition, an understanding of the flow phenomena within the ladle during operation can provide industry with key knowledge necessary to improve the efficiency and throughput of the process.</p> <p> </p> <p>The method by which this research aims to address this is through the development of a comprehensive computational fluid dynamics (CFD) model of the steelmaking ladle. Such a model, capable of predicting the inclusion removal process and flow patterns within the ladle, would serve to provide the necessary information to advance steelmaking efficiency and improve product quality. A full scale unsteady state three dimensional CFD model has been developed to predict removal of inclusion during gas-stirring in a ladle. The Eulerian-Eulerian model was used to simulate the multiphase flow, the Population Balanced Model (PBM) has been used to describe the inclusion distribution. The phenomena of bottom-blow argon bubble coalescence and breakup were considered. </p> <p> </p> <p>Additionally, a model has been developed to predict inclusion removal during operation. For the inclusion removal model, the CFD-PBM coupled method has been proposed to investigate the inclusion behavior. This includes representing phenomena such as inclusion-bubble collision, inclusion removal by attachment to the ladle refractory, and inclusion capture by slag floating on the surface of the melt. The unified computational model for simulation of fluid flow and inclusion removal was validated against industry measurements provided by Nucor Steel. </p> <p> </p> <p>Using this CFD model and a ladle geometry and set of baseline conditions provided by Nucor Steel, studies were carried out to examine flow development, gas bubble distribution, and inclusion removal. Examining the impacts of inclusion size on removal rate indicated that larger inclusions are removed faster. This agreed with both industry expectations and data found in published literature. In addition, the model predicts that bubble-inclusion collision are primarily responsible for 99% inclusion removal in a gas-stirred ladle.</p>

The main aim of this research was to investigate the mechanism of cavitation in conforming and partially conforming tribological conjunctions. The effect of cavitation on load carrying capacity and frictional performance of is also investigated. This is important with regards to fuel efficiency in internal combustion (IC) engines. Friction accounts for 15–20% of IC engine losses. The piston–cylinder system contributes to 40–50% of these, with the compression ring(s) being responsible for most of this. This is because the primary function of the ring is to seal the combustion chamber, thus small emerging gaps lead to increased friction. In fact, compression ring(s) expend 3–5% of engine input fuel energy. The share of frictional losses of engine bearings is approximately 20–25%. Traditionally, prediction of performance of tribological conjunctions has been studied using Reynolds equation. When the effect of cavitation is considered, various cavitation algorithms with associated boundary conditions for lubricant rupture and reformation are proposed. These include Elrod, and Elrod and Coyne algorithms, as well as boundary conditions such as Swift-Stieber, JFO and Prandtl-Hopkins. There are a number of assumptions embodied in these approaches, as well as the use of Reynolds equation itself. These approaches do not uphold the continuity of mass and momentum in multi-phase flow, in cavitation beyond the lubricant film rupture. A detailed methodology for multi-phase flow, comprising simultaneous solution of Navier-Stokes, energy and lubricant rheological state equations is developed.

Made available in DSpace on 2014-06-12T17:38:50Z (GMT). No. of bitstreams: 2 arquivo6453_1.pdf: 4622041 bytes, checksum: ed8506dd3b53ef28252dacc7bded0d0c (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2011 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho apresenta uma avaliação de ferramentas e métodos para elaboração de mapas eólicos aplicados a projetos de centrais eólicas. Os mapas eólicos têm como função a determinação do potencial eólico local e servem de base para a locação de turbinas eólicas. Os modelos estudados estão implementados em ferramentas amplamente utilizadas no meio eólico: WAsP e o WindSim. Essas ferramentas apresentam parâmetros de entrada padrão que quando não ajustados podem resultar em extrapolações errôneas, visto a não representação correta do ambiente estudado. Para o estudo foi utilizado um ano de dados de intensidade e direção do vento provenientes da campanha de medição de duas torres anemométricas, com medições em três níveis de altura (20, 50 e 78 metros), localizadas numa região de complexidade topográfica moderada no interior da Paraíba - Brasil. Na primeira análise a comparação é realizada entre os valores calculados através de extrapolações das medições nas torres e os valores medidos nas torres, sem alterar os parâmetros padrão das ferramentas. Nesta análise, o modelo CFD do WindSim apresentou desvio médio quadrático de 2,18%, enquanto o modelo WAsP apresentou desvio médio quadrático de 10,21%, quando comparado com as medições nas torres. Na segunda análise os parâmetros de entrada do WAsP foram corrigidos para que fossem mais representativos para a atmosfera local, com ênfase para o parâmetro que representa a estabilidade atmosférica. A estabilidade atmosférica foi modelada através do gradiente vertical de temperatura medido na região estudada, com medições de temperatura em dois níveis de altura. Com esse ajuste o desvio médio quadrático do WAsP para a segunda análise diminuiu para 6,80%. Na terceira análise foram comparados todos os pontos dos mapas eólicos gerados pelo WAsP e pelo WindSim para área de interesse. Neste caso, verificou-se sobre estimativas na velocidade do vento de até 21% do mapa eólico WAsP em relação ao WindSim e sub estimativas de até 23%

Diploma thesis deals with numerical simulations of an air flow in a water cooled charge air cooler (WCAC), specifically with pressure drops in inlet/outlet chamber. The simulations have been performed in a proprietary software Star-CCM+. Physical phenomena have been solved by the Reynolds-averaged Navier-Stokes (RANS) equations and consequently a matrix of pressure drops for miscellaneous variations of chamber's geometry and the initial flow conditions has been created. Based on the CFD results, dependence between calculated pressure drops and changing parameters has been analyzed and finally a 1D solver has been developed and implemented into a software OpenModelica.

Tese de mestrado integrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 2010

Aerosolized drug delivery to the human lungs for asthma treatment has long been studied and yet the relationship between the delivery efficacy and the inter-subject variability due to gender, age, and disease severity remains unclear. A recent imaging-based cluster analysis on a population of asthmatic patients identifies four clusters with distinct structural and functional characteristics. The use of cluster membership to explore inter-subject variability by investigating numerically the air flow and particle transport in representative subjects of the asthmatic clusters on inhalation drug delivery in asthma sub-populations is proposed. Large-eddy simulations using computed tomography (CT)-based airway models were performed with a slow and deep breathing profile corresponding to application of a metered dose inhaler. Physiologically consistent subject specific boundary conditions in peripheral airways were produced using an image registration technique and a resistance network compliance model. Particle simulations and final deposition statistics were calculated for particle sizes ranging from 1–8 μm. The results suggested an emphasis on the importance of airway constriction for regional particle deposition and prominent effects of local features in lobar, segmental, and sub-segmental airways on overall deposition patterns. Asthmatic clusters characterized by airway constriction had an increase in deposition efficiency in lobar, segmental, and sub-segmental airways. Local constrictions produced jet flows that impinged on distal bifurcations and resulted in large inertial depositions. Decreased right main bronchus (RMB) branching angle decreased the fraction of particles ventilated to the right upper lobe (RUL). Cluster-based computational fluid dynamics results demonstrate particle deposition characteristics associated with imaging based variables that could be useful for future drug delivery improvements. One method for circumventing low deposition in small airways due to constriction in tracheobronchial airways is through hygroscopic growth of aerosols for inhalation. Hygroscopic materials have an affinity for water and can enlarge in size significantly as they traverse through respiratory tract. Hygroscopic growth has shown promise as a viable drug delivery method for decreasing deposition in the upper tracheobronchial region and increasing drug penetration and retention in small airways. Current models for hygroscopic growth models show promise in predicting steady state final diameter aerosol droplet sizes, but much uncertainty in predicting transient effects exists. This paper discusses in detail one such growth model and modifies it to include realistic spatial temperature and humidity variations associated with the lung. The growth model is simplified through grouping of terms and is then solved using MATLAB ODE 45 solver. The model is compared to experimentally acquired in vitro data for validation. The results do not show good agreement with the model, and suggests that additional factors exist that inhibit aerosol droplet growth from commencing immediately upon entering the respiratory tract like is assumed true in literature. This paper briefly hypothesizes for reasons for model and data disagreement and limitations of current growth models.

The safety of migrating salmon, especially salmonids, in the Pacific Northwest has been a concern for decades. With the advent of fish bypass systems, and safer turbines the focus of salmon safety has turned to total dissolved gases. Produced by entrainment of air into tailrace waters, total dissolved gases (TDG) can cause gas bubble disease, a harmful and potential lethal disease in fish. Avian predators are another danger for migrating salmon. In some areas of the world birds common in the Pacific Northwest can account for as much as 65% of salmon smolt losses. The goal of this thesis is to determine the effects of changing operational conditions at McNary dam on fish exposure to predator habitats and TDG. Computational fluid dynamic models were implemented to predict the hydrodynamics, TDG distribution and inert particle trajectories in the tailrace of McNary dam for varying operational conditions. A 3D volume of fluid (VOF) model was used first to capture the free surface shape in the tailrace. A rigid-lid model was then used to simulate the hydrodynamics and TDG distribution within the tailrace using the free surface shape from the VOF model. This 3D two phase model utilized an anisotropic Reynolds Stress turbulence model. All grids were generated using the commercial Gridgen software. A lagrangian particle tracking model that followed Newton's laws of motion were used to track inert particles throughout the domain. Validation of the model was performed. A grid refinement study with four different refinement levels was performed. Velocities for each grid type were compared against field data taken in 2004, and TDG was compared amongst the four grids. It was determined the medium level of refinement could accurately predict the velocities, and the TDG was relatively independent of grid density; TDG averages at the grid outlets were within 1.435% of one another. The TDG distribution was then compared, using the grid of medium refinement against field data measured in 1997and were between 1.5 and 3% of error depending on the transect. After validation of the model 16 predictive simulations were run with varying levels of total river flow and operational conditions. Tailrace hydrodynamics along with TDG production and distribution were compared for simulations with comparable total river flow rates. Fish trajectories were tracked using the particle tracking model. Inert particles were injected into the domain and properties such as velocity, distance to the shore and depth about each were recorded. Statistics were then generated for the particles based on criteria that defined dangerous predation zones within the tailrace. After completion of the simulations, it was determined that existing operations consistentlyproduced higher levels of TDG due to increased entrainment of the powerhouse flows into the spillway regions. It was also found that with increasing total river flows, TDG levels increased. On average, summer operations had lower TDG than spring due to the lower total river flows. Predation zones were similar for all simulations, but particle statistics varied depending on operational conditions. In general, particles were safer for higher flowrates as fewer low velocity eddies where particles could be trapped formed in simulations with high flowrates.

There is increasing interest in assessing the role of hemodynamics in aneurysm growth and rupture mechanism. Identification of the indicators of rupture risk can prove very valuable in the clinical management of patients. If rupture risk of aneurysms can be predicted, immediate preemptive treatments can be done for the high risk patients whereas others can avoid the risky intervention. Retrospective studies have been performed in the past to filter out indices that differentiate ruptured aneurysms from unruptured aneurysms. However, these differences may not necessarily translate to differences between aneurysms that present unruptured but fork towards growth/rupture and unruptured aneurysms that are invariably stable. The hypothesis of the present study is that hemodynamic indices of unruptured aneurysms when they first presented can be used to predict their longitudinal outcome. A prospective longitudinal cohort study was designed to test this hypothesis. Four clinical centers participated in this study and a total of 198 aneurysms were recruited. These aneurysms were chosen by the physicians to be kept under watchful waiting. Three-dimensional models of aneurysms and their contiguous vasculature generated using the initial scans of patients were used for computational fluid dynamic (CFD) simulations. Both pulsatile and steady flow analyses were performed for each patient. By collating all the prominent hemodynamic indices available in aneurysm literature and developing a few new indices, 25 hemodynamic indices were estimated for each subject. For statistical analysis, it was hypothesized a priori that low wall shear area is different between stable and unstable aneurysms. All other indices were tested in a post-hoc manner. The longitudinal outcome information of these patients was recorded at the clinical centers and the author was blinded until all analyses were complete. Aneurysms that grew during the follow up period were labeled as "grown" and otherwise they were called "stable" by the radiologists. After the hemodynamic analysis was complete, a non-parametric Mann Whitney U test was performed to determine if any index can statistically differentiate the two groups ("grown" versus "stable"). It was found that none of the indices distinguished the two groups with statistical significance. Comparison of the steady and pulsatile flow analysis suggested that the patient population is stratified in the same order by an index, irrespective of whether the index is computed using a steady or pulsatile flow simulation. Pearson correlation coefficient was obtained between basic geometric indices and hemodynamic indices of this population. No strong correlation was found in between morphology and hemodynamics, suggesting uniqueness of the hemodynamic indices. The hypothesis motivating the present study is that aneurysm blood flow based indices can be used as prognostic indicators of growth and/or rupture risk. This study is the first to analyze intracranial aneurysm hemodynamics of a large cohort in a longitudinal prospective manner. Results of the present study indicate that quantitative hemodynamics cannot be used to predict the longitudinal outcome of an aneurysm. Further studies are needed to gain additional clinical insights.

In the bio/pharmaceutical industry, fermentation is extremely important in pharmaceutical development, and in microbial research. However, new fermentor designs are needed to improve production and reduce costs of complex systems such as cultivation of mammalian cells and genetically engineered micro-organisms. Traditionally, stirred tank design is driven by the oxygen transfer capability needed to achieve cell growth. However, design methodologies available for stirred tank fermentors are insufficient and many times contain errors. The aim of this research is to improve the design of production scale stirred tank fermentors through the development of dimensionless correlations and by providing information on aspects of fermentor tanks that can aid in oxygen mass transfer. This was accomplished through four key areas. Empirical studies were used to quantify the mass transfer capabilities of several different reactors. Computational fluid dynamics (CFD) was used to assess the impact of certain baffle and impeller geometries. Correction schemes were developed and applied to the experimental data. Dimensionless correlations were created from corrected experimental data to act as a guide for future production scale fermentor design. The methods for correcting experimental data developed in this research have proven to be accurate and useful. Furthermore, the correlations found from the corrected experimental data in this study are of great benefit in the design of production scale stirred tank fermentors. However, when designing a stirred tank fermentor of a different size, further experimentation should be performed to refine the correlations presented.

A microfluidic device was created for single-cell capture and analysis using polydimethylsiloxane (PDMS) channels and a glass substrate to develop a microfluidic single-cell impedance sensor for cell diagnostics. The device was fabricated using photolithography to create a master mold which in turn will use soft lithography to create the PDMS components for constant device production. The commercial software, COMSOLTM Multiphysics, was used to quantify the fluid dynamics in shallow micro-channels. The device will be able to capture a cell and sequester it long enough to enable measurement of the impedance spectra that can characterize cell. The proposed device will be designed to capture a single cell and permit back-flow to flush out excess cells in the chamber. The device will be designed to use syringe pumps and the syringe-controlled channel will also be used to capture and release the cell to ensure cell control and device reusability. We hypothesize that these characteristics along with other proposed design factors will result in a unique microfluidic cell-capture device that will enable single-cell impedance sensing and characterization.