Water utilities in Nova Scotia face numerous challenges treating low turbidity water and complying with stringent guidelines and treatment standards. Problems associated with the treatment of low-turbidity water are not confined to Nova Scotia; several other provinces, British Columbia, Manitoba and Ontario share similar water characteristics of drinking water sources. The treatment of low turbidity water is a challenge for these utilities as it requires maintaining the appropriate coagulant dosage that will ensure adequate particle and natural organic matter removal, while at the same time not enhancing the formation of disinfection by-products. Another concern associated with the treatment of such water is that when the particle content of the water is very low, charge neutralization will not be effective due to the weak contact between destabilized particles. Currently, nanoparticles are not regulated as water contaminants, and thus it is unclear whether the existing filtration treatment practices are capable of removing them from drinking water. Obtaining in-depth information on nanoparticle characteristics in drinking water sources will provide a valuable resource that can assist in the development of future treatment strategies. In this research, characteristics of four synthetic nanoparticles cerium dioxide (CeO2), ferric oxide (Fe2O3), silicon dioxide (SiO2) and titanium dioxide (TiO2) were investigated in Milli-Q water for particle size, surface area, and surface potential using different characterization techniques. Water samples from Pockwock Lake were also characterized for naturally occurring nanoparticles. After initial testing, titanium dioxide (TiO2) nanoparticles were selected to examine particle removal at bench-scale filtration experiments, under operating conditions similar to those practiced at the J.D. Kline Water Supply Plant, Halifax, NS, Canada. Filter performance for the deposition of TiO2 nanoparticles was evaluated through the calculation of its attachment efficiency and coefficient under various water chemistry conditions. The calculated filter efficiency was then applied to simulate natural nanoparticles removal from water. The results of the research indicate that the investigated nanoparticles behaved similar to natural particles and formed aggregates with larger particle sizes in Milli-Q water. Among the tested nanoparticles, only titanium dioxide could be coagulated with alum, as its negative surface charge and zero point of charge were closer to that of alum. Filtration experiments revealed that TiO2 nanoparticles, when present in water, could successfully be removed by an alum dose of 8 mg/L. Indeed, removal in excess of 99.5% was achieved under the study conditions. Under the investigated water chemistry conditions, very low attachment efficiencies (?) of 0.001, 0.002 and 0.01, and filter coefficients (?) of -0.003, -0.001 and -0.02 were determined for the filters. Based on the calculated attachment efficiencies, and under the studied conditions, natural nanoparticles remain dispersed in the water and would not likely to be removed by direct filtration. The overall research findings represent a major step forward in nanoparticle removal by direct filtration.

Abstract Interactions between the components of papermaking suspensions (e.g. fibres, fillers, fines and polymers) have a remarkable effect on various unit processes in papermaking. The filterability of fibre suspensions, which is a crucial property for example in paper sheet forming and solid recovery, is also known to be depended on particle interactions. However, due to the complex nature of the interactions, the role of these phenomena in fibre suspension filtration is still not fully understood. The focus of this thesis was to find out how phenomena associated to fibre flocculation, fibre deflocculation and filler particle deposition affect the filterability of fibre suspensions in terms of their dewaterability and retention. It was shown that the influence of fibre flocculation on dewatering is closely related to the structure of fibre flocs. More importantly, the internal density of flocs and factors that impacted the packing structure of filter cakes, such as floc size, played a crucial role in fibre suspension dewaterability. Dense flocs with a low internal porosity particularly induces fast water flow by a mechanism termed as the “easiest path mechanism” through the large voids around the flocs. The effect of fibre suspension dispersing on dewaterability and particularly fines retention was found to be associated to the mechanism of action of the deflocculation agent. Carboxymethylcellulose (CMC), the deflocculant used in this study, had detrimental effects on the dewatering of a pulp suspension both when being adsorbed on fibre surfaces and when remained in the liquid phase. However, adsorbed CMC causes more plugging of the filter cake because it disperses the fines more profoundly. Thus the adsorbed CMC also reduces fines retention considerably more than CMC did in the liquid phase. Filler deposition and retention was found to be significantly higher on pulp fines fractions of mechanical and chemical pulp than on fibre fractions due to the higher external surface area of fines. The surface charge densities of pulp fractions also affected their ability to adsorb fillers. Cationic charges of filler particles was in turn observed to induce deposition of fillers on fibre surfaces which increased retention but also the dewaterability of a fibre suspension due to a decrease in total surface area of a suspension.

Theoretical and experimental studies of particle deposition in turbulent pipe flow have been carried out for over forty years, but some of the most important transport mechanisms are still not well understood. The first part of this thesis is concerned with the calculation of particle density when using Lagrangian methods to predict inertial particle transport in two-dimensional laminar fluid flows. Traditionally, Lagrangian calculations involve integrating the particle equations of motion along particle pathlines, and the particle density is obtained by applying a statistical averaging procedure to those pathlines which intersect a particular computational grid cell. Unfortunately, extremely large numbers of particles are required to reduce the statistical errors to acceptable levels, and this makes the method computationally expensive. Recently, the Full Lagrangian approach has been developed, which allows the direct calculation of the particle density along particle pathlines. This method had previously been applied only to simple analytical flow fields. The application of the method to CFD generated fluid velocity fields was shown to be possible, and the results obtained using the Full Lagrangian approach were compared to those from a traditional Lagrangian approach. It was found that better quality solutions could be obtained with the use of far fewer particle pathlines. An analysis of the manner in which the Full Lagrangian approach deals with particles whose paths cross each other (and the resulting discontinuity in particle density) was also undertaken, and this illustrates the sophistication of the method. The second part of the thesis comprises an experimental and theoretical study of the deposition of small particles in turbulent flows by thermophoresis. Thermophoresis is the phenomenon whereby small particles suspended in a gas in which there exists a temperature gradient experience a force in the direction opposite from that of the temperature gradient. Previous researchers have attempted to impose a radial temperature difference in pipe flow experiments, but have not yet succeeded in attaining a constant thermophoretic force along the length of the pipe. This limits the accuracy and usefulness of the data for the validation of theoretical expressions for the thermophoretic fluxes. An experimental rig has been designed to achieve a constant thermophoretic force. This was done by using an annular geometry with a cold inner wall and hot outer wall. The particle size was varied and the deposition flux was measured for turbulent flow with three temperature differences. The deposition fluxes for small particles were found to be independent of dimensionless particle size, with each increase in temperature difference resulting in an increase in magnitude of the flux. Evidence of a thermophoresis-turbulence coupling was found for intermediate-sized particles, and large particles were not influenced by thermophoresis. A theory of particle deposition, developed for the case of turbulent pipe flow, was modified to study flow in a turbulent annulus, so that theoretical expressions for the thermophoretic fluxes could be included and compared with the experimental results. Agreement with experimental data was quite good, but some deficiencies in a widely used theoretical expression for the thermophoretic flux were exposed. An alternative expression was used, which gave much better agreement with the experimental data, and the mechanisms behind the thermophoresis-turbulence coupling were also investigated. The validation of this expression for the thermophoretic force will allow its inclusion in numerical studies of particle deposition in more complex geometries.

No description available.

Evropská legislativa požaduje snížení počtu zvířat zapojených do laboratorních testů. Současně je známo velmi málo o sekundárních účincích plynných látek (např. Deodorantů, čisticích sprejů) používaných denně v každé domácnosti. Na základě těchto potřeb byla provedena analýza transportu a reziduí částic v dýchacích cestách. Studie byla provedena ve dvou částech: teoretická část - simulace CFD, praktická část ověření. Experimentální část výzkumu je založen na modulu simulátoru plic i-Lung. Modul může být použit i jako pasivní i aktivní simulátor plic.

This research investigates the efficacy of liquid-precursor thermal spray coating (TSC) as a facile wood modification technique to bring hydrophobicity and UV durability to a wooden surface. The technique was successful in depositing Cu and TiO2 particles onto southern yellow pine (SYP) veneers by using copper azole, copper quaternary, and titanium tetraisopropoxide as the precursor solutions. Using optimized settings, the average coating surface coverage of > 90% and an average coating thickness of > 5 μm were obtained. The coatings displayed up to 4H rating in the film hardness scale and up to 3B rating in adhesion strength scale, suggesting reasonable mechanical durability under mild mechanical abrasion. TSC-modified wood with TiO2 created a water repellent layer, yielding a significant increase in hydrophobicity that changed the water contact angle from 57° to 126°. Accelerated weathering test results showed that the TSC-modified wood was more resistant to discoloration compared to unmodified wood.

This dissertation presents a detailed account of the study undertaken on the subject of fouling of Exhaust Gas Recirculator (EGR) coolers. The fouling process in EGR coolers is identified to be due to two primary reasons — deposition of fine soot particles and condensation of hydrocarbons known as dry soot and wet soot fouling, respectively. Several numerical simulations are performed to study the fouling process. Preliminary analysis of the particle forces for representative conditions reveal that drag, thermophoresis and Brownian forces are the significant transport mechanisms and among them, the deposition process is dominated by thermophoresis. Soot deposition in a representative turbulent plain channel shows a direct relationship of the amount of deposition with the near-wall temperature gradient. Subsequently, periodic and developing flow simulations are performed on a wavy channel geometry, a common EGR design for various Reynolds numbers and thermal boundary conditions. Constant heat flux boundary condition is used in the periodic fully-developed calculations, which assist in establishing various deposition trends. The wavy nature of the walls is noted to affect the fouling process, resulting in specific deposition patterns. For the lower Reynolds number flows, significantly higher deposition is observed due to the higher particle residence times. On the other hand, the developing flow calculations facilitate the use of wall temperature distributions that typically exist in EGR coolers. The linear dependence of the amount of deposition on the near-wall temperature gradient or in other words, the heat flux, is ascertained. It is also observed in all the calculations, that for the sub-micron soot particles considered, the deposition process is almost independent of the particle size. In addition, the nature of the flow and heat transfer characteristics and the transition to turbulence in a developing wavy channel are studied in considerable detail. Finally, a study on the condensation of heavy hydrocarbons is undertaken as a post-processing step, which facilitates the prediction of the spatial distribution and time-growth of the combined fouling layer. From the calculations, the maximum thickness of the dry soot layer is observed to be near the entrance, whereas for the wet soot layer, the peak is found to be towards the exit of the EGR cooler. Further, parametric studies are carried out to investigate the effect of various physical properties and inlet conditions on the process of fouling. / Master of Science

This thesis presents a computational framework that models the coupled behavior between sand deposits and their surrounding fluid. Particle deposits that form in gas turbine engines and industrial burners, can change flow dynamics and heat transfer, leading to performance degradation and impacting durability. The proposed coupled framework allows insight into the coupled behavior of sand deposits at high temperatures with the flow, which has not been available previously. The coupling is done by using a CFD-DEM framework in which a physics based collision model is used to predict the post-collision state-of-the-sand-particle. The collision model is sensitive to temperature dependent material properties of sand. Particle deposition is determined by the particle's softening temperature and the calculated coefficient of restitution of the collision. The multiphase treatment facilitates conduction through the porous deposit and the coupling between the deposit and the fluid field. The coupled framework was first used to model the behavior of softened sand particles in a laminar impinging jet flow field. The temperature of the jet and the impact surface were varied(T^* = 1000 – 1600 K), to observe particle behavior under different temperature conditions. The Reynolds number(Rejet = 20, 75, 100) and particle Stokes numbers (Stp = 0.53, 0.85, 2.66, 3.19) were also varied to observe any effects the particles' responsiveness had on deposition and the flow field. The coupled framework was found to increase or decrease capture efficiency, when compared to an uncoupled simulation, by as much as 10% depending on the temperature field. Deposits that formed on the impact surface, using the coupled framework, altered the velocity field by as much as 130% but had a limited effect on the temperature field. Simulations were also done that looked at the formation of an equilibrium deposit when a cold jet impinged on a relatively hotter surface, under continuous particle injection. An equilibrium deposit was found to form as deposited particles created a heat barrier on the high temperature surface, limiting more particle deposition. However, due to the transient nature of the system, the deposit temperature increased once deposition was halted. Further particle injection was not performed, but it can be predicted that the formed deposit would begin to grow again. Additionally, a Large-Eddy Simulation (LES) simulation, with the inclusion of the Smagorinsky subgrid model, was performed to observe particle deposition in a turbulent flow field. Deposition of sand particles was observed as a turbulent jet (Re jet=23000,T_jet^*= 1200 K) impinged on a hotter surface(T_surf^*= 1600 K). Differences between the simulated flow field and relevant experiments were attributed to differing jet exit conditions and impact surface thermal conditions. The deposit was not substantive enough to have a significant effect on the flow field. With no difference in the flow field, no difference was found in the capture efficiency between the coupled and decoupled frameworks. / Master of Science

Dlouhodobé vdechování částic může přispívat ke vzniku nebo zhoršení nejrůznějších plicních onemocnění. Na druhou stranu, vdechování léčiv je často používanou metodou podávání léků proti astmatu a jiným nemocem dýchacího ústrojí. V obou případech je důležité dobře porozumět mechanismům, na jejichž základě funguje pohyb částic a jejich usazování v dýchacích cestách. Cílem této disertační práce bylo získat nová experimentální data depozice částic a analyzovat vliv tvaru částic a průtoku vzduchu na depozici. Byla studována depozice porézních a vláknitých částic v realistickém modelu dýchacích cest. Porézní částice byly vyrobeny různými metodami, např. sprejovým sušením nebo metodou krystalizace. Takto vyrobené částice byly použity při depozičních experimentech. Detekce částic byla provedena pomocí UV/VIS spektrofotometrie. Vláknitý aerosol byl vytvořen rozdrcením skelné vaty. Takto vzniklé vláknité částice byly několikrát prosety přes řadu sít a dále roztříděny podle délky pomocí klasifikátoru pracujícím na principu dielektroforézy. Následná depozice byla vyhodnocena použitím mikroskopie s fázovým kontrastem. Ke zrychlení analýzy byl vyvinut program, který dokáže na základě analýzy obrazu najít a spočítat vlákna. Výsledky experimentu byly použity k určení depozičních charakteristik. S jejich pomocí pak byl kvantifikován vliv tvaru částic a průtoku na míru usazování. Depoziční účinnost částic rostla v závislosti na Stokesově čísle, což poukazuje na vliv setrvačnosti při usazování částic. Bylo prokázáno, že depoziční účinnost porézních částic je podobná té u částic kulových při stejném Stokesově čísle. Vláknité částice se usazovali méně efektivně v porovnání s kulovými částicemi majícími stejné Stokesovo číslo. Jelikož byly okrajové podmínky dostatečně popsány a model plic je k dispozici i v digitální podobě, je možné data použít k validaci výsledků numerických simulací.

La protection des opérateurs et la surveillance des ambiances de travail en cas de mise en suspension d’aérosols radioactifs, dans un local ventilé d’une installation nucléaire, requièrent la connaissance de l’évolution spatio-temporelle de la concentration en particules, en tout point du local considéré. L’estimation précise de cette concentration a fait l’objet du développement de modèles spécifiques de transport et de dépôt d’aérosols dans un local ventilé, dans le cadre d’une thèse cofinancée par l’IRSN et EDF, en collaboration avec l’IMFT. Un formalisme eulérien de glissement est utilisé pour modéliser le transport des aérosols. Celui-ci est basé sur une unique équation de transport des concentrations en particules (« Diffusion-Inertia model »). L’étude spécifique du dépôt d’aérosols en parois a permis de développer un modèle de couche limite, qui consiste à déterminer précisément le flux de dépôt de particules en parois, quels que soient le régime de dépôt et l’orientation de la surface considérée. Les modèles de transport et de dépôt finalement retenus ont été implantés dans Code_Saturne, un logiciel de mécanique des fluides. La validation de ces modèles a été effectuée à partir de données de la littérature en géométries simples, puis sur la base de campagnes expérimentales de traçage dans des locaux ventilés d’environ 30 m³ et 1500 m³. / When particulate radioactive contamination is likely to become airborne in a ventilated room, assessment of aerosol concentration in every point of this room is important, in order to ensure protection of operators and supervision of workspaces. Thus, a model of aerosol transport and deposition has been developed as part of a project started with IRSN, EDF and IMFT. A simplified eulerian model, called “diffusion-inertia model” is used for particle transport. It contains a single transport equation of aerosol concentration. The specific study of deposition on walls has permitted to develop a boundary condition approach, which determines precisely the particle flux towards the wall in the boundary layer, for any deposition regime and surface orientation.The final transport and deposition models retained have been implemented in a CFD code called Code_Saturne. These models have been validated according to literature data in simple geometries and tracing experiments in ventilated rooms, which have been carried out in 30 m³ and 1500 m³ laboratory rooms.