Sparse-Lagrangian PDF Modelling of Silica Synthesis from Silane Jets in Vitiated Co-flows with Varying Inflow Conditions

This paper presents a comparison of experimental and numerical results for a series of turbulent reacting jets where silica nanoparticles are formed and grow due to surface growth and agglomeration. We use large-eddy simulation coupled with a multiple mapping conditioning approach for the solution of the transport equation for the joint probability density function of scalar composition and particulate size distribution. The model considers inception based on finite-rate chemistry, volumetric surface growth and agglomeration. The sub-models adopted for these particulate processes are the standard ones used by the community. Validation follows the “paradigm shift” approach where elastic light scattering signals (that depend on particulate number and size), OH- and SiO-LIF signals are computed from the simulation results and compared with “raw signals” from laser diagnostics. The sensitivity towards variable boundary conditions such as co-flow temperature, Reynolds number and precursor doping of the jet is investigated. Agreement between simulation and experiments is very good for a reference case which is used to calibrate the signals. While keeping the model parameters constant, the sensitivity of the particulate size distribution on co-flow temperature is predicted satisfactorily upstream although quantitative differences with the data exist downstream for the lowest coflow temperature case that is considered. When the precursor concentration is varied, the model predicts the correct direction of the change in signal but notable qualitative and quantitative differences with the data are observed. In particular, the measured signals show a highly non-linear variation while the predictions exhibit a square dependence on precursor doping at best. So, while the results for the reference case appear to be very good, shortcomings in the standard submodels are revealed through variation of the boundary conditions. This demonstrates the importance of testing complex nanoparticle synthesis models on a flame series to ensure that the physical trends are correctly accounted for

An Experimental and Computational Investigation into Laser-Based Synthesis and Spectrochemical Characterizations of Metal/intermetallic Nanoparticles with Engineered Interfacial Functionalities

Nanomaterials have, over the years, generated tremendous interests of scientists and engineers from nearly all disciplines. This interest has been due to a large number of desired physico-chemical properties such as magneto-optic properties, mechanical strength, melting points, charge transport behavior, and surface reactivity exhibiting unique size-dependent characteristics at the nanoscale. The unique interfacial properties are widely believed to be a result of high ratio of surface to bulk atoms as well as, bridging states in which nanoparticles exist between atomic and bulk materials. Thus, in the world of material processing and engineering, recent years have seen a surge in the use of wide classes of nanostructured materials as novel energetic, catalytic, semiconductor, and biomedical materials with engineered functionalities that find use in industrial, technological and defense applications. Therefore, it becomes imperative to develop fundamental understanding on the manufacturing and characterization routes that can allow the systematic tuning of the interfacial-property characteristics of advanced nanomaterials by tailoring their sizes and architectures. The current PhD thesis aims to address this grand-challenge engineering problem by investigating early-stage formations theoretically, synthesis and novel spectrochemical characterizations of advanced metal/intermetallic and composite nanoparticles (NPs) with engineered surface properties. Specifically, the thesis is categorized into two broad sections, namely laser-based synthesis studies and laser-based spectroscopic characterizations of NPs. The synthesis section presents theoretical investigations into the inception stage of NP formations, namely nucleation via numerical simulations. Briefly, this section aims to reveal the processing-structure-property relations of metal NPs synthesized via gas phase routes in an effort to relate the processing parameters to the size and morphology of the NPs, which in turn, dictates their interfacial energetic and catalytic behaviors. Then, using the obtained fundamental understandings a laser-based synthesis technique is presented for generating novel energetic metallic nanocomposites. The size, morphology and energetic activities of these materials are analyzed and tuned to improve the energetic properties. Finally, the laser spectroscopic characterization section focuses on experimental investigations by introducing laser induced breakdown spectroscopy (LIBS) as a relatively non-destructive and robust spectrochemical technique for the structural and chemical composition characterizations of composite NPs in a facile, yet effective manner

New Particle Formation in the Remote Marine Boundary Layer

Marine low clouds play an important role in the climate system, and their properties are sensitive to cloud condensation nuclei concentrations. While new particle formation represents a major source of cloud condensation nuclei globally, the prevailing view is that new particle formation rarely occurs in remote marine boundary layer over open oceans. Here we present evidence of the regular and frequent occurrence of new particle formation in the upper part of remote marine boundary layer following cold front passages. The new particle formation is facilitated by a combination of efficient removal of existing particles by precipitation, cold air temperatures, vertical transport of reactive gases from the ocean surface, and high actinic fluxes in a broken cloud field. The newly formed particles subsequently grow and contribute substantially to cloud condensation nuclei in the remote marine boundary layer and thereby impact marine low clouds

Modeling of Turbulent Sooting Flames

Modeling multiphase particles in turbulent fluid environment is a challenging task. To accurately describe the size distribution, a large number of scalars need to be transported at each time-step. Add to that the heat release and species mass fraction changes from nonlinear combustion chemistry reactions, and you have a tightly coupled set of equations that describe the (i) turbulence, (ii) chemistry, and (iii) soot particle interactions (physical agglomeration and surface chemistry reactions). Uncertainty in any one of these models will inadvertently introduce errors of up to a few orders of magnitude in predicted soot quantities. The objective of this thesis is to investigate the effect of turbulence and chemistry on soot evolution with respect to different soot aerosol models and to develop accurate models for simulating soot evolution in aircraft combustors. To investigate the effect of small scale turbulence time-scales on soot evolution, a partially-stirred reactor (PaSR) configuration is used and coupled with soot models from semi-empirical to detailed statistical models. Differences in soot property predictions including soot particle diameter and number density among the soot models are highlighted. The soot models will then be used to simulate the turbulent sooting flame in an aircraft swirl combustor to determine the large scale soot-turbulence-chemistry interactions. Highlights of this study include the differences in location of bulk soot mass production in the combustor using different soot models. A realistic aircraft combustor operating condition is simulated using a state-of-the-art minimally dissipative turbulent combustion solver and soot method of moments to investigate pressure scaling and soot evolution in different operating conditions. A separate hydrodynamic scaling is introduced to the pressure scaling, in addition to thermochemical scaling from previous studies. Finally, a Fourier analysis of soot evolution in the combustor will be discussed. A lower sooting frequency mode is found in the combustor, separate from the dominant fluid flow frequency mode that could affect statistical data collection for soot properties in turbulent sooting flame simulations.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147513/1/stchong_1.pd

Ultra-Small Metal Nanoparticles: Aerosol- and Laser-Assisted Nanomanufacturing, Characterization, and Applications

Ultrasmall metal nanoparticles (1-10 nm) are certain to be the building blocks of the next generation of electronic, catalytic, and energy storage devices. Despite their importance, synthesizing these extremely small nanoparticles, at least in sufficient quantities to enable their industrial utility however, is challenging due to their low stability and tendency to agglomerate. Numerous techniques developed thus far typically generate metal nanoparticles in small quantities with a main difficulty in industrial scale-up being poor thermal control. This shortcoming often leads to wide size distributions, inhomogeneous dispersion, and aggregation. Thus, there is a pressing need for developing new strategies for scalable manufacturing of ultrasmall metal nanoparticles towards industrial applications. This dissertation identifies two techniques for scalable manufacturing of ultrasmall metal nanoparticles with tunable size, constituency, microstructure, and other properties: an aerosol droplet mediated approach and an ultrafast laser shock approach. The aerosol droplet mediated approach employs the fast heating and quenching nature of aerosol droplet nanoreactors containing precursor species to produce ultrasmall metal nanoparticles uniformly dispersed in polymer or graphene matrices. The fast heating and quenching nature intrinsic to the aerosol droplets is also employed to fabricate a new type of engineering material, notably high entropy alloy nanoparticles, defined as five or more well-mixed metal elements in near equimolar ratios. As an example of application, I further employ the aerosol droplets to create antimony nanoparticles incorporated carbon nanosphere network and the resulting architecture offered one of the best potassium ion battery anode performances in terms of both capacity and cycling stability. This dissertation also introduces an ultrafast laser shock technique to decorate metal nanoparticles onto carbon nanofibers (CNFs) in-situ with kinetically tunable size and surface density. A shorter laser shock enables the formation of metal nanoclusters with higher number densities and smaller sizes while longer laser shock leads to the further growth of metal nanoclusters and the achievement of their equilibrium shape. The catalytic performance towards electrocatalytic hydrogen evolution was greatly enhanced for CNF supported metal nanoclusters with a smaller size and higher number density

Development of drinking water treatment processes for nanoparticles removal

The ability of drinking water treatments (DWT) to remove ENPs from water is crucial to ensure the safety of public water supply. This thesis assessed the removal of three comercial metal-based nanoparticles, titanium dioxide (TiO2), silver (Ag) and copper oxide (CuO) in DWT, exploring and comparing the potential of conventional and advanced processes. To understand the removal mechanisms, individual ENPs and mixtures of the three ENPs, dispersed in synthesised and natural surface waters were used. Conventional coagulation/ flocculation/ sedimentation (C/F/S) process alone and enhanced with powdered activated carbon (PAC) were studied, and the advanced membrane filtration processes, ultrafiltration (UF) and nanofiltration (NF), were integrated with conventional C/F/S (hybrid water treatment) or used alone (NF). These technologies were evaluated under typical DWT operational conditions. Overall, results show that optimised treatments are able to remove ENPs, without hampering other DWT target compounds. Residual turbidity, dissolved organic carbon, specific UV absorbance and aluminium were below the guidelines and similar to those found in actual DWTP. C/F/S removed 93% and 98% of the tested ENPs, depending on water characteristics. C/F/S+PAC and C/F/F→UF treatments improved the removal of single and multiple ENPs in approximately 10% compared with C/F/S alone, with Ti and Cu undetected in the C/F/S→UF treated water. However, due to AgNPs dissolution, residual Ag concentrations were present in the C/F/S→UF treated water. Using NF, the dissolved Ag was eliminated from treated water to undetectable values (depending on water characteristics). The main mechanisms responsible for the removal were charge neutralisation (C/F/S), size exclusion (UF and NF), adsorption and complexation with salts and adsorption on NOM (PAC and NF). This study contributes to the advancement of knowledge on the removal of emerging contaminants from drinking water, demonstrating that the processes optimisation for the ENPs removal is a key factor to ensure safe water, reducing the potential hazards associated to the ingestion of these contaminants and meeting the drinking water quality guidelines.A capacidade de controlar e manipular a forma e o tamanho de estruturas à escala nanométrica veio revolucionar diversas áreas industriais, possibilitando a criação de produtos adaptáveis, mais eficientes e de baixo custo através da integração de nanomateriais manufaturados, especialmente nanopartículas (NPs). Contudo, o crescimento exponencial de produtos do quotidiano contendo NPs leva à introdução destas nanoestruturas no meio aquático, originando potenciais riscos toxicológicos tanto para o ambiente como para a saúde humana. As características intrínsecas das NPs, tais como tamanho reduzido, forma variada, área superficial elevada, assim como as suas capacidades de agregação e dissolução, proporcionam uma maior reatividade, podendo ampliar o seu efeito tóxico e tornando-as responsáveis por efeitos nocivos nos organismos vivos. A introdução de NPs manufaturadas em águas superficiais utilizadas para a produção de água para consumo apresenta um elevado risco para a saúde humana, uma vez que pode levar à exposição direta às NPs através da ingestão de água contaminada. A ingestão de NPs pode causar efeitos adversos à saúde humana, tais como problemas renais, inflamações gastrointestinais, implicações ao nível do sistema neurológico e doenças cancerígenas. Embora ainda existam algumas dúvidas relacionadas com a toxicidade destas nanoestruturas, algumas NPs já foram identificadas como tóxicas para a saúde humana, nomeadamente as de origem metálica, onde se incluem as NPs de TiO2, Ag e CuO. Atualmente, já foram detetadas NPs em águas superficiais, águas para consumo humano e em água da torneira com concentrações entre os ng/L e os μg/L. Embora o tratamento de água seja uma das principais estratégias para evitar a exposição humana às NPs através da ingestão, os poucos estudos existentes descrevem os tratamentos convencionais como sendo ineficientes na sua remoção. Estes estudos, para além de mostrarem uma elevada variabilidade nas eficiências de remoção, foram maioritariamente realizados usando elevadas concentrações de NPs dispersas em água ultrapura, da torneira ou soluções sintéticas, sem considerarem a complexidade das águas superficiais naturais. Assim sendo, este trabalho pretendeu estudar a capacidade dos tratamentos de água convencionais e avançados para remover nanopartículas de águas superficiais. Para tal, a remoção de NPs de origem metálica foi explorada e avaliada usando diversas estratégias de tratamento, de modo a garantir uma eficiente remoção de NPs e de iões provenientes da sua dissolução. Os tratamentos propostos tiveram também por base a minimização do impacte da requalificação das estações de tratamento de águas para consumo humano recuperando os processos mais utilizados na produção de água potável. Para os ensaios foram escolhidas nanopartículas manufaturadas disponíveis comercialmente, TiO2, Ag e CuO, com base na sua elevada produção e aplicação em produtos do quotidiano. De modo a compreender os mecanismos de remoção, as NPs foram usadas individualmente e em conjunto dispersas em águas sintéticas (águas modelo) e águas naturais provenientes de barragens (Alentejo e Algarve) atualmente utilizadas para a produção de água para consumo humano. Em todas as opções de tratamento estudadas, os processos foram sempre otimizados tendo em vista a maximização da remoção das NPs, aplicando condições operacionais típicas em contexto real de tratamento de água. O tipo e doses de coagulante e carvão ativado testados são também usados em contexto real. O tratamento convencional coagulação/floculação/sedimentação (C/F/S) demonstrou ter capacidade para remover NPs, tanto em águas sintéticas como naturais, utilizando um coagulante polimérico de alumínio. Este processo apresentou eficiências elevadas (ca. 95%) tanto na remoção das NPs individualmente, como na sua remoção simultânea (variando entre 93% e 99% dependendo da NP e das características da água. Contudo, foi observado que para alcançar remoções semelhante de NPs de TiO2, as águas hidrofóbicas necessitam de uma dose de coagulante mais elevada do que as hidrofílicas. Ao contrário das características das águas, a presença de diferentes NPs em conjunto não afetou a dose de coagulante necessária. Determinou-se que o mecanismo de remoção de NPs mais provável foi a neutralização de cargas. No final do processo, as concentrações residuais de NPs nas águas tratadas foram, 6.5±2.1 e 2.5±0.7 μg Ti/L, 15.0±1.4 e 6.0±1.4 μg Ag/L, e 18.8±8.8 e 0.5±0.1 μg Cu/L, para a água natural com menor turvação e matéria orgânica natural (NOM) e para a água natural com maior turvação e NOM, respetivamente. De modo a diminuir as concentrações residuais de NPs na água tratada, o processo convencional C/F/S foi combinado com a adsorção por carvão ativado em pó (C/F/S+PAC) e integrado com o tratamento avançado ultrafiltração (UF) num processo de tratamento híbrido (C/F/S→UF). O processo C/F/S+PAC foi mais eficiente na remoção das NPs de TiO2 (>99.9%), com o Ti a apresentar concentrações inferiores ao limite de deteção na água tratada. Para o mesmo tratamento as remoções de Ag e Cu foram superiores a 99.2%. Com a aplicação do tratamento híbrido (C/F/S→UF), não foram detetadas concentrações residuais nem de Ti nem de Cu na água filtrada. Contudo, foram detetadas concentrações entre 5.0 e 7.0 μg/L para a Ag. Este resultado foi associado à dissolução das AgNPs, uma vez que, tendo em conta o menor tamanho do poro da membrana comparado com o tamanho individual das NPs e dos agregados formados, a parte nanoparticulada foi removida. Com o intuito de remover tanto AgNPs, como os iões provenientes da dissolução foi utilizado o tratamento avançado de nanofiltração (NF). Com este tratamento os agregados e as nanopartículas individuais foram completamente removidas por exclusão de tamanho, tendo a remoção de Ag dissolvida chegado aos 99.9%, dependendo do conteúdo de sais e matéria orgânica natural das águas testadas. Os resultados obtidos permitem concluir que é possível remover de forma eficaz NPs durante o tratamento de água para consumo humano, utilizando uma combinação/sequência de tratamentos convencionais e avançados, sem prejudicar a qualidade da água final. Tal foi demonstrado pela comparação dos valores residuais de turvação, carbono orgânico dissolvido, SUVA (absorvência específica) e alumínio com os valores paramétricos nacionais e internacionais para a água para consumo humano. Uma linha de tratamento integrando C/F/S+PAC, seguido de UF ou até mesmo NF, apresenta-se como uma solução segura para eliminar a ameaça de ingestão de NPs através de água potável.PhD Grant (SFRH/BD/100402/2014) from the Portuguese Foundation of Science and Technology, trough the European Social Found from European Union. CENSE – Center for Environmental and Sustainability Research which financed by national funds FCT/MCTES (UID/AMB/04085/2019)

Experimental and Numerical Investigation of Molten Salt Nanomaterials for Enhanced Thermal Energy Storage (TES) and Heat Transfer Fluid (HTF)

Concentrating solar power (CSP) plants have been widely commercialized internationally for generating electricity from solar energy. Thermal energy storage (TES) systems are typically used in CSP plants to balance the fluctuations in demand with the intermittency of supply. In various CSP plants, molten salts are used as both the primary heat transfer fluid (HTF) and as TES medium. However, molten salts suffer from poor thermo-physical properties, e.g., specific heat capacity is typically less than 2 J/(g·K) and thermal conductivity is typically less than ~1 W/(m·K). Doping molten salts with minute quantities of nanoparticles has been shown to enhance their thermo-physical properties (also known as molten salt nanofluids). Stable dispersion of nanoparticles realized in different solvents (i.e., nanofluids) has been demonstrated to cause anomalous enhancement in the resulting thermo-physical property values. Traditional approaches employed for mixing nanoparticles in solvents often results in agglomeration and precipitation (fouling). This results in compromised reliability and not being cost-effective for industrial applications, such as in CSP plants. In this study, an innovative one-step synthesis protocol was developed and the techno-economic feasibility of using the molten salt nanofluids was explored for CSP applications. Modulated Differential Scanning Calorimetry (MDSC) and TemperatureHistory (T-History) method were used to measure the specific heat capacity of the nanomaterial samples at high temperatures (~500 °C). In addition, the thermal conductivity of the nanofluid samples were also measured using a customized concentric cylinder test apparatus. Solar salt (NaNO₃-KNO₃) was used as the neat solvent (base fluid) material. Various nanoparticles (SiO₂, Al₂O₃, MgO, ZnO) were either procured directly from commercial suppliers or generated in-situ from chemical reactions. Different parameters were explored in the synthesis: nanoparticle type, concentration, synthesis temperature, synthesis time, dispersing agents, etc. Numerical models were developed to elucidate the mechanism of specific heat capacity enhancement of the synthesized nanomaterials and to explore the thermal-hydraulic performance of molten salt nanofluid samples in a flow loop. Molecular dynamics (MD) simulations were performed to elucidate the morphology of the compressed layer formed due to adsorption of the solvent molecules on the surface of a nanoparticle surface. Chemical kinetics simulations were performed to predict the nucleation and growth rate of ensembles of nanoparticles during one-step synthesis. CFD simulations were performed to predict the heat transfer coefficient of the molten salt nanofluids in a flow loop. The results from the experimental and numerical investigation demonstrated that the one-step synthesis protocol for nanofluids involving generation of nanoparticles in-situ from cheap additives is a cheap and cost-effective approach for industrial applications (e.g., CSP) for enhancing the energy storage capacity and power rating as well as for extending the life-cycle of equipment (e.g., heat exchangers)

New MRI Techniques for Nanoparticle Based Functional and Molecular Imaging

Although in clinical use for several decades, magnetic resonance imaging: MRI) is undergoing a transition from a qualitative anatomical imaging tool to a quantitative technique for evaluating myriad diseases. Furthermore, MRI has made great strides as a potential tool for molecular imaging of cellular and tissue biomarkers. Of the candidate contrast agents for molecular MRI, the excellent bio-compatibility and adaptability of perfluorocarbon nanoparticles: PFC NP) has established these agents as a potent targeted imaging agent and as a functional platform for non-invasive oxygen tension sensing. Direct readout and quantification of PFC NP can be achieved with fluorine: 19F) MRI because of the unique 19F signal emanating from the core PFC molecules. However, the signal is usually limited by the modest accumulated concentrations as well as several special NMR considerations for PFC NP, which renders 19F MRI technically challenging in terms of detection sensitivity, scan time, and image reconstruction. In the present dissertation, some of the pertinent NMR properties of PFC NP are investigated and new 19F MRI techniques developed to enhance their performance and expand the biomedical applications of 19F MRI with PFC NP. With the use of both theoretical and experimental methods, we evaluated J-coupling modulation, chemical shift and paramagnetic relaxation enhancement of PFC molecules in PFC NP. Our unique contribution to the technical improvement of 19F MRI of small animal involves:: 1) development of general strategies for RF 1H/19F coil design;: 2) design of novel MR pulse sequences for 19F T1 quantification; and: 3) optimization of imaging protocols for distinguishing and visualizing multiple PFC components: multi-chromatic 19F MRI). The first pre-clinical application of our novel 19F MRI techniques is blood vessel imaging and rapid blood oxygen tension measurement in vivo. Blood vessel anatomy and blood oxygen tension provide pivotal physiological information for routine diagnosis of cardiovascular disease. Using our novel Blood: flow)-Enhanced-Saturation-Recovery: BESR) sequence, we successfully visualized reduced flow caused by thrombosis in carotid arteries and jugular veins, and we quantified the oxygen tension in the cardiac ventricles of the mouse. The BESR sequence depicted the expected oxygenation difference between arterial and venous blood and accurately registered the response of blood oxygen tension to high oxygen concentration in 100% oxygen gas. This study demonstrated the potential application of PFC NP as a blood oxygen tension sensor and blood pool MR contrast agent for angiography. Another pre-clinical application investigated was functional kidney imaging with 19F MRI of circulating PFC NP. Conventional functional kidney imaging typically calls for the injection of small molecule contrast agents that may be nephrotoxic, which raises concerns for their clinical applications in patients with renal insufficiency. We demonstrated that our 19F MRI technique offers a promising alternative functional renal imaging approach that generates quantitative measurement of renal blood volume and intrarenal oxygenation. We successfully mapped the expected heterogeneous distribution of renal blood volume and confirmed the presence of an oxygenation gradient in healthy kidneys. We validated the diagnostic capability of 19F MRI in a mouse model of acute ischemia/reperfusion kidney injury. We also employed 19F MRI as a tool to test the therapeutic efficacy of a new nanoparticle-based drug, i. e. PPACK: D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone) PFC NP, which was postulated to inhibit microvascular coagulation during acute kidney injury. Based on our preliminary 19F MRI findings, we observed that PPACK PFC NP effectively reduced coagulation in our animal model, as evidenced by lesser accumulation of particles trapped by the clotting process. This finding suggests the potential for 19F MRI to be used as a drug monitoring tool as well in common medical emergencies such as acute kidney failure