Traditional methods of studying underground coal mine explosions are limited to observations and data collected during experimental explosions. These experiments are expensive, time-consuming, and require major facilities, such as the Lake Lynn Experimental Mine. The development of computational fluid dynamics (CFD) modeling of explosions can help minimize the need for large-scale testing. This thesis utilized the commercial CFD software, SC/Tetra, to examine three case studies. The first case study modeled the combustion of methane in a scaled shock tube, measuring approximately 1 foot by 1 foot, by 20.5 feet long, with a methane cloud of 2.5 feet in length, at a concentration of 9% methane. The numerical results from the CFD model were in good agreement with experimental data gathered, with all pressure peaks within 0.25 psi of the recorded pressure data. However, the model had an extensive run-time of 16 hours to reach the peak pressures. The second case study modeled the same explosion, but utilized a total pressure boundary condition at the location of the membrane, instead of the combustion of methane. A pressure-time curve was assigned to this boundary, recreating the release of pressure by the explosion. This was made possible with the knowledge of the experimental data. The numerical results from the CFD model were in excellent agreement with experimental data gathered, with all pressure peaks within 0.07 psi of the recorded pressure data. Alternatively, this model had a run-time of 40 minutes. The third case study modeled a methane explosion in a large shock tube, measuring 8 feet by 8 feet, by 40 feet long, with a methane cloud of 4 feet in length, at a concentration of 9% methane. The bursting balloon technique was employed, which did not model the combustion of methane, but instead the equivalent energy release. The numerical results from the CFD model were in good agreement with the experimental data gathered, with all pressure peaks within 0.025 psi of the recorded pressure data. Additionally, the numerical results modeled the negative pressure phenomenon observed in the experimental results, caused by suction or negative pressure created by the blast wave, immediately following the positive wave. This model had a run-time of 20 minutes. The results of this researched provided validation that there are alternative ways to successfully model methane explosion, without having to model the chemical reactions involved in the combustion of methane, providing quicker run-times and in this case, more accurate results.

<p>1D engine simulations of turbocharged engines are difficult to <!-- @page { size: 21cm 29.7cm; margin: 2cm } P { margin-bottom: 0.21cm } --></p><p>Techniques that can increase the SI- engine efficiency while keeping the emissions very low is to reduce the engine displacement volume combined with a charging system. Advanced systems are needed for an effective boosting of the engine and today 1D engine simulation tools are often used for their optimization.</p><p>This thesis concerns 1D engine simulation of a turbocharged SI engine and the introduction of CFD computations on components as a way to assess inaccuracies in the 1D model.</p><p>1D engine simulations have been performed on a turbocharged SI engine and the results have been validated by on-engine measurements in test cell. The operating points considered have been in the engine’s low speed and load region, with the turbocharger’s waste-gate closed.</p><p>The instantaneous on-engine turbine efficiency was calculated for two different turbochargers based on high frequency measurements in test cell. Unfortunately the instantaneous mass flow rates and temperatures directly upstream and downstream of the turbine could not be measured and simulated values from the calibrated engine model were used. The on-engine turbine efficiency was compared with the efficiency computed by the 1D code using steady flow data to describe the turbine performance.</p><p>The results show that the on-engine turbine efficiency shows a hysteretic effect over the exhaust pulse so that the discrepancy between measured and quasi-steady values increases for decreasing mass flow rate after a pulse peak.</p><p>Flow modeling in pipe geometries that can be representative to those of an exhaust manifold, single bent pipes and double bent pipes and also the outer runners of an exhaust manifold, have been computed in both 1D and 3D under steady and pulsating flow conditions. The results have been compared in terms of pressure losses.</p><p>The results show that calculated pressure gradient for a straight pipe under steady flow is similar using either 1D or 3D computations. The calculated pressure drop over a bend is clearly higher1D engine simulations of turbocharged engines are difficult to <!-- @page { size: 21cm 29.7cm; margin: 2cm } P { margin-bottom: 0.21cm } -->using 1D computations compared to 3D computations, both for steady and pulsating flow. Also, the slow decay of the secondary flow structure that develops over a bend, gives a higher pressure gradient in the 3D calculations compared to the 1D calculation in the straight pipe parts downstream of a bend.</p><p> </p>

abstract: Proton exchange membrane fuel cells (PEMFCs) run on pure hydrogen and oxygen (or air), producing electricity, water, and some heat. This makes PEMFC an attractive option for clean power generation. PEMFCs also operate at low temperature which makes them quick to start up and easy to handle. PEMFCs have several important limitations which must be overcome before commercial viability can be achieved. Active areas of research into making them commercially viable include reducing the cost, size and weight of fuel cells while also increasing their durability and performance. A growing and important part of this research involves the computer modeling of fuel cells. High quality computer modeling and simulation of fuel cells can help speed up the discovery of optimized fuel cell components. Computer modeling can also help improve fundamental understanding of the mechanisms and reactions that take place within the fuel cell. The work presented in this thesis describes a procedure for utilizing computer modeling to create high quality fuel cell simulations using Ansys Fluent 12.1. Methods for creating computer aided design (CAD) models of fuel cells are discussed. Detailed simulation parameters are described and emphasis is placed on establishing convergence criteria which are essential for producing consistent results. A mesh sensitivity study of the catalyst and membrane layers is presented showing the importance of adhering to strictly defined convergence criteria. A study of iteration sensitivity of the simulation at low and high current densities is performed which demonstrates the variance in the rate of convergence and the absolute difference between solution values derived at low numbers of iterations and high numbers of iterations. / Dissertation/Thesis / M.S.Tech Chemistry 2011

La radiothérapie interne sélective est une thérapie émergente très peu invasive du carcinome hépatocellulaire, quatrième cause de décès par cancer dans le monde. Des millions de microsphères chargées en Yttrium 90 sont injectées dans l'artère hépatique par un cathéter. Actuellement, leur distribution lors d'une injection est estimée par l'injection préliminaire d'un radiomarqueur, ce qui peut se révéler trop approximatif. Un traitement personnalisé permettrait une concentration des radiations à la tumeur tout en épargnant le tissu sain environnant. Dans ce travail je me suis intéressée au développement d'un modèle numérique, pour une simulation spécifique à chaque patient des trajectoires des microsphères, dans le but d'optimiser le traitement. Le protocole clinique d'imagerie a été exploité et optimisé pour l'extraction de données spécifiques patients telles que le foie, les tumeurs, l'artère hépatique et le flux sanguin. Les tissus et l'artère hépatique (jusqu'à un diamètre de 0.05 mm) sains et malins ont été simulés. Cela nous permet de simuler la distribution des microsphères dans le tissue hépatique, validée grâce à la scintigraphie post-traitement. Il est supposé ici que les microsphères se distribuent de façon proportionnelle au flux sanguin, lequel est modélisé par la loi de Poiseuille. Des simulations plus approfondies en mécanique de fluides numérique du flux sanguin ont ensuite été réalisées dans l'artère hépatique du patient. Pour cela nous avons utilisé et comparé les méthodes des Volumes Finis (Ansys Fluent) et de Lattice Boltzmann (programme développé dans le laboratoire). Le transport des microsphères a été simulé dans l'artère hépatique du patient avec la méthode des volumes finis, et dans une géométrie simplifiée avec la méthode de Lattice Boltzmann. Une séquence IRM de contraste de phase a aussi été optimisée pour l'extraction de la vitesse du sang dans l'artère hépatique, dans le but de valider le modèle numérique. / Selective internal radiation therapy using Yttrium-90 loaded glass microspheres injected in the hepatic artery is an emerging, minimally invasive therapy of hepatocellular carcinoma, which is the fourth cause of mortality in the world. Currently, microspheres distribution can be only approximately predicted by the injection of a radiotracer, whose behaviour may be different. A personalised intervention can lead to high concentration dose in the tumour, while sparing the surrounding parenchyma. This work is concerned with the development of a patient-specific numerical model for the simulation of microspheres trajectories and treatment optimisation. Clinical imaging protocol is utilised and optimised in order to extract patient’s specific data such as liver, tumours, hepatic artery and blood flow. Normal and malignant hepatic arterial vasculature and tissues are simulated down to a vessels diameter of 0.05 mm. A preliminary simulation of microspheres distribution in liver tissue is proposed and validated against post-treatment scintigraphy. Microspheres are here supposed to distribute proportionally to blood flow, which is computed based on Poiseuille’s law. More precise computational fluid dynamics (CFD) simulations of blood flow in the patient’s segmented arteries are performed. The Finite Volume Method (Ansys Fluent) and the Lattice Boltzmann Method (in-house developed software) are used to this purpose and their efficacy is compared. Microspheres transport is simulated in the patient’s hepatic artery using the FVM, and in a representative geometry using the LBM method. A phase contrast MRI sequence has been optimised in order to extract blood velocity from the hepatic artery and validate CFD simulations.

This Master’s thesis is dedicated to a generation of an additional torque, which can occur due to the inaccuracy of the manufacturing. This issue is inspired by a real case from 2013. In this work CFD modeling is used to investigate three different sources of the additional torque: misalignment of the rudder, deviation of the propeller shaft and asymmetry of the rudder. A simplified 2D simulation is done for all three cases. This simulation is more suitable for a jet powered boat. Therefore the asymmetry of the rudder is investigated also in a 3D case, where the rotational component of the flow behind the propeller is included.

<p>Fouling is a critical issue in commercial food manufacturing. Fouling can cause biofilm formation and pose a threat to the safety of food products. Early detection of fouling can lead to informed decision making about the product’s safety and quality, and effective system cleaning to avoid biofilm formation. In this study, a Non-Intrusive Continuous Sensor (NICS) was designed to estimate the thermal conductivity of the product as they flow through the system at high temperatures as an indicator of fouling. Thermal properties of food products are important for product and process design and to ensure food safety. Online monitoring of thermal properties during production and development stages at higher processing temperatures, ~140°C like current aseptic processes, is not possible due to limitations in sensing technology and safety concerns due to high temperature and pressure conditions. Such an in-line and noninvasive sensor can provide information about fouling layer formation, food safety issues, and quality degradation of the products. A computational fluid dynamics model was developed to simulate the flow within the sensor and provide predicted data output. Glycerol, water, 4% potato starch solution, reconstituted non-fat dry milk (NFDM), and heavy whipping cream (HWC) were selected as products with the latter two for fouling layer thickness studies. The product and fouling layer thermal conductivities were estimated at high temperatures (~140°C). Scaled sensitivity coefficients and optimal experimental design were taken into consideration to improve the accuracy of parameter estimates. Glycerol, water, 4% potato starch, NFDM, and HWC were estimated to have thermal conductivities of 0.292 ± 0.006, 0.638 ± 0.013, 0.487 ± 0.009, 0.598 ± 0.010, and 0.359 ± 0.008 W/(m·K), respectively. The thermal conductivity of the fouling layer decreased as the processing time increased. At the end of one hour process time, thermal conductivity achieved an average minimum of 0.365 ± 0.079 W/(m·K) and 0.097 ± 0.037 W/(m·K) for NFDM and HWC fouling, respectively. The sensor’s novelty lies in the short duration of the experiments, the non-intrusive aspect of its measurements, and its implementation for commercial manufacturing.</p>

Techniques that can increase the SI- engine efficiency while keeping the emissions very low is to reduce the engine displacement volume combined with a charging system. Advanced systems are needed for an effective boosting of the engine and today 1D engine simulation tools are often used for their optimization. This thesis concerns 1D engine simulation of a turbocharged SI engine and the introduction of CFD computations on components as a way to assess inaccuracies in the 1D model. 1D engine simulations have been performed on a turbocharged SI engine and the results have been validated by on-engine measurements in test cell. The operating points considered have been in the engine’s low speed and load region, with the turbocharger’s waste-gate closed. The instantaneous on-engine turbine efficiency was calculated for two different turbochargers based on high frequency measurements in test cell. Unfortunately the instantaneous mass flow rates and temperatures directly upstream and downstream of the turbine could not be measured and simulated values from the calibrated engine model were used. The on-engine turbine efficiency was compared with the efficiency computed by the 1D code using steady flow data to describe the turbine performance. The results show that the on-engine turbine efficiency shows a hysteretic effect over the exhaust pulse so that the discrepancy between measured and quasi-steady values increases for decreasing mass flow rate after a pulse peak. Flow modeling in pipe geometries that can be representative to those of an exhaust manifold, single bent pipes and double bent pipes and also the outer runners of an exhaust manifold, have been computed in both 1D and 3D under steady and pulsating flow conditions. The results have been compared in terms of pressure losses. The results show that calculated pressure gradient for a straight pipe under steady flow is similar using either 1D or 3D computations. The calculated pressure drop over a bend is clearly higher1D engine simulations of turbocharged engines are difficult to using 1D computations compared to 3D computations, both for steady and pulsating flow. Also, the slow decay of the secondary flow structure that develops over a bend, gives a higher pressure gradient in the 3D calculations compared to the 1D calculation in the straight pipe parts downstream of a bend. / QC 20101119

Following an unexpected event in an underground mine, it is important to know the state of the mine immediately to manage the situation effectively. Particularly when part or the whole mine is inaccessible, remotely and quickly ascertaining the ventilation status is one of the pieces of essential information that can help mine personnel and rescue teams make decisions. This study developed a methodology that uses tracer gas techniques and CFD modeling to analyze underground mine ventilation system status remotely. After an unanticipated event that has damaged ventilation controls, the first step of the methodology is to assess and estimate the level of the damage and the possible ventilation changes based on the available information. Then CFD models will be built to model the normal ventilation status before the event, as well as possible ventilation damage scenarios. At the same time, tracer gas tests will be designed and performed on-site. Tracer gas will be released at a designated location with constant or transient release techniques. Gas samples will be collected at other locations and analyzed using Gas Chromatography (GC). Finally, through comparing the CFD simulated results and the tracer on-site test results, the general characterization of the ventilation system can be determined. A review of CFD applications in mining engineering is provided in the beginning of this dissertation. The basic principles of CFD are reviewed and six turbulence models commonly used are discussed with some examples of their application and guidelines on choosing an appropriate turbulence model. General modeling procedures are also provided with particular emphasis on conducting a mesh independence study and different validation methods, further improving the accuracy of a model. CFD applications in mining engineering research and design areas are reviewed, which illustrate the success of CFD and highlight challenging issues. Experiments were conducted both in the laboratory and on-site. These experiments showed that the developed methodology is feasible for characterizing underground ventilation systems remotely. Limitations of the study are also addressed. For example, the CFD model requires detailed ventilation survey data for an accurate CFD modeling and takes much longer time compared to network modeling. Some common problems encountered when using tracer gases in underground mines are discussed based on previously completed laboratory and field experiments, which include tracer release methods, sampling and analysis techniques. Additionally, the use of CFD to optimize the design of tracer gas experiments is also presented. Finally, guidelines and recommendations are provided on the use of tracer gases in the characterization of underground mine ventilation networks. / Ph. D.

Computational fluid dynamics (CFD) modeling and analysis were used in three projects: solar CO2 conversion modeling, improved coal combustion modeling using STAR-CD, and premixed combustion modeling. Each project is described below. The solar CO2 conversion modeling project involved CFD simulations of a prototype solar CO2 converter that uses sunlight to dissociate CO2 into CO and O2. Modeling was used to predict the performance of this prototype converter using three CFD software packages, and involved predicting the flow, heat transfer, and chemical kinetics. Accuracy was determined by comparison of model predictions and experimental data. Parametric modeling studies were performed in order to better understand converter performance and limitations. Modeling analysis led to proposed operational and design changes meant to improve converter performance. Modeling was performed to quantify the effects of proposed design modifications and operational adjustments. Modeling was also used to study the effects of pressure, some geometric design changes, and changing from pure CO2 to a CO2/He mixture. The insights gained from these modeling studies have played a key role in improving the performance of this process. The second project involved the implementation of advanced coal models into STAR-CD, a commercial CFD program. These coal models were originally developed for PCGC-3, a code developed at Brigham Young University. This project involved modifying modern PCGC-3 coal combustion and gasification models so that they could be incorporated into STAR-CD. Models implemented included a coal set-up subroutine, and coal reactions models for devolatilization, char oxidation, and vaporization. Each implemented model was tested to verify its accuracy by comparison of model predictions with experimental data. All implemented coal submodels were validated by comparison between overall modeling predictions and experimental data. These implemented coal models increased the capability of STAR-CD to model coal combustion and gasification systems. The third project was to assemble previously obtained experimental data on lean, premixed natural gas combustion. Velocity, temperature, and species concentration measurements were previously taken throughout a laboratory-scale gas turbine combustor using advanced laser diagnostics. However, these data were taken by different investigators at BYU over the course of 10 years, and the data were scattered through several publications, theses, and dissertations. This third project was to compile these data into a central location for analysis and distribution. This data set is excellent for validation of any comprehensive combustion model, and is now accessible to the public.

Synfuel from gasification of coal, biomass, and/or petroleum coke is an alternative to natural gas in land-based industrial gas turbines. However, carryover fine particulate in the syngas may lead to a considerable amount of deposition on turbine blades, which reduces component life and system performance. Deposition experiments on film-cooled turbine components were performed in an accelerated test facility to examine the nature of flyash deposits near film cooling holes. Experimental results indicate that deposition capture efficiency decreased with increased blowing ratio. Shaped holes exhibited more span-wise coverage than cylindrical holes and effectively reduced deposition. The TBC layer increased surface temperature, resulting in increased deposition. Coupons with close hole spacing exhibited a more uniform low temperature region downstream and less deposition. Capture efficiencies for small particles were lower than for large particles, especially at low blowing ratios. The trench increased cooling effectiveness downstream, but did not reduce overall collection efficiency of particulates because the trench also acted as a particulate collector. In the numerical computations using a CFD code (FLUENT), the standard k-ω turbulence model and RANS were employed to compute flow field and heat transfer. A Lagrangian particle method was utilized to predict the ash particulate transport. User-defined subroutines were developed to describe and predict particle deposition rates on the turbine blade surface. Small particles had a greater tendency to stick to the surface. As the surface temperature rose above the transition temperature, large particles dominated the excessive deposition due to the high delivery rate. Backside impingement of coolant improved the overall cooling effectiveness. Experiments and CFD modeling results suggest that clean coolant dominated the initial deposition process by blowing off the particles and preventing particles from impacting on the surface. Initial deposits formed between coolant channels. Subsequent deposition occurred on top of initial deposits, due to increasing deposit surface temperature, which led to the formation of distinct ridges between coolant paths.