Orientador: Watson Loh / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-07T11:45:40Z (GMT). No. of bitstreams: 1 Anselmo_AleteiaGarcia_M.pdf: 1348079 bytes, checksum: 03480ee468bf0185ae57c464c2020046 (MD5) Previous issue date: 2006 / Resumo: Neste trabalho estudou-se a partição do poli (óxido de propileno), PPO, poli (N - isopropilacrilamida), PNIPAM, poli (N-vinil-2- pirrolidona), PVP, e poli (óxido de etileno), PEO em sistemas líquidos bifásicos, entre as fases aquosa e orgânica (CHCI3, CH2Cl2 e C6H5CI). Os resultados obtidos indicaram que a partição do PPO, polímero hidrofóbico, é preferencial para as fases orgânicas em todos os sistemas bifásicos estudados, enquanto que para os polímeros hidrofílicos, tais como, o PVP e PNIPAM, a partição ocorre preferencialmente para a fase aquosa. As entalpias de transferência, da fase aquosa para a fase orgânica para estes polímeros, foram determinadas através da técnica de titulação calorimétrica isotérmica e revelaram que para todos os sistemas estudados o processo de transferência é endotérmico. Isto sugere que a solvatação dos polímeros pela fase aquosa é mais energética que quando comparada com a solvatação dos polímeros pela fase orgânica, e que, portanto, para o PPO, o processo de transferência é entropicamente dirigido. Spitzer e colaboradores observaram resultados similares para a partição do poli (óxido de etileno), PEO, em sistemas bifásicos contendo CHCl3 e CH2Cl2, (Spitzer et aI.; J. Phys. Chem. B 2002, 106, 12448). Em comparação com o PEO, os valores de entalpia de transferência obtidos para o PPO são mais positivos, o mesmo pode ser observado para o coeficiente de partição. A partição do PPO pode ser explicada em termos de efeito hidrofóbico, o qual propõe a liberação das moléculas de água que estariam solvatando o polímero quando este é transferido para a fase orgânica. / Abstract: In this work the partitioning of poly (propylene oxide), PPO, poly (Nisopropylacrylamide), PNIPAM, poly (vinyl pyrrolidone), PVP and poly (ethylene oxide), PEO between aqueous and organic phases (CHCI3, CH2Cl2 and C6H5CI) was investigated. The results reveal that for all biphasic systems the partitioning of PPO, a hydrophobic polymer, to organic phase is predominant, while for PVP and PNIPAM, hydrophilic polymers, partitioning is always preferential towards the aqueous phase. The enthalpies of transfer for these polymers from aqueous to organic phases were calorimetrically determined and revealed an endothermic process for all the systems investigated, suggesting that solvatation of polymers in aqueous phase is more energetic than organic phase and, therefore, the process of transfer must be entropically driven for PPO. Spitzer and coworkers observed similar results for the partitioning of PEO in biphasic systems containing CHCl3 and CH2Cl2, (Spitzer et aI.; J. Phys. Chem. B 2002, 106, 12448). In comparison with PEO, the enthalpies of transfer of PPO are more positive, the same being observed for the partition coefficients. These data indicate that partitioning of PPO can be explained within the framework of the hydrophobic effect, whereby water molecules that were originally solvating the polymer are released when this is transferred to the organic phase. / Mestrado / Físico-Química / Mestre em Química

abstract: Computability of spray flows is an important issue, from both fundamental and practical perspectives. Spray flows have important applications in fuel injection, agriculture, medical devices, and industrial processes such as spray cooling. For this reason, many efforts have been devoted to experimental, computational and some theoretical aspects of spray flows. In particular, primary atomization, the process of bulk liquid transitioning to small droplets, is a central and probably the most difficult aspect of spray flows. This thesis discusses developed methods, results, and needed improvements in the modeling of primary atomization using a predictive Sauter Mean Diameter (SMD) formula. Primary atomization for round injectors and simplex atomizers is modeled using a three-step procedure. For each spray geometry, a volume-of-fluid simulation is run to resolve the trajectory of the intact liquid core. Atomization criterion is applied to the volume-of-fluid velocity field to determine atomization sites. Local droplet size is predicted at the atomization sites using the quadratic formula for Sauter Mean Diameter. Droplets with the computed drop size are injected from the atomization sites and are tracked as point-particles. A User Defined Memory (UDM) code is employed to compute steady-state Sauter Mean Diameter statistics at locations corresponding to experimental interrogation locations. The resulting Sauter Mean Diameter, droplet trajectory, and droplet velocity are compared against experimental data to validate the computational protocol. This protocol can be implemented on coarse-grid, time-averaged simulations of spray flows, and produces convincing results when compared with experimental data for pressure-atomized sprays with and without swirl. This approach is general and can be adapted in any spray geometry for complete and efficient computations of spray flows. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2020

Stirling engines are an external combustion heat engine that converts thermal energy into mechanical work that a closed cycle is run by cyclic compression and expansion of a work fluid (commonly air or Helium) in which, the working fluid interacts with a heat source and a heat sink and produces network. The engine is based on the Stirling cycle which is a subset of the Carnot cycle. The Stirling cycle has recently been receiving renewed interest due to some of its key inherent advantages. In particular, the ability to operate with any form of heat source (including external combustion, flue gases, alternative (biomass, solar, geothermal) energy) provides Stirling engines a great flexibility and potential benefits since it is convinced as engines running with external heat sources. However, several aspects of traditional Stirling engine configurations (namely, the Alpha, Beta, and Gamma), specifically complexity of design, high cost, and relatively low power to size and power to volume ratios, limited their widespread applications to date. This study focuses on an innovative Stirling engine configuration that features a rotary displacer (as opposed to common reciprocating displacers), and aims to utilize analytical and numerical analysis to gain insights on its operation parameters. The results are expected to provide useful design guidelines towards optimization. The present study starts with an overview of the Stirling cycle and Stirling engines including both traditional and innovative rotary displacer configurations, and their major advantages and disadvantages. The first approach considers an ideal analytical model and implements the well-known Schmidt analysis assumptions for the rotary displacer Stirling engine to define the effects of major design and operation parameters on the performance. The analytical model resulted in identifying major variables that could affect the engine performance (such as the dead volume spaces, temperature ratios and the leading phase angle). It was shown that the dead volume could have a drastic effect over the engine performance and the optimum phase angle of the engine is 90o. The second approach considers a non-ideal analytical model and aims to identify and account the main sources of energy losses in the cycle to better represent the engine performance. The study showed that the ideal efficiency and the non-ideal efficiency could have 15% difference that could have as an enormous effect on the engine performance.

The study involves development of a methodology to simulate a fin-tube evaporator under icing conditions using CFD in Ansys® Academic Fluent 2021R1. It aims to build on previous studies performed on heat pumps. It was performed by Abhay M. Hervatte in collaboration with Bosch Thermoteknik AB, Tranås, SE during the spring term of the year 2021. The thesis is published by Linköping University. Initially, experiments were conducted to measure the ice growth on the fins of the evaporator as a function of time. A CAD model of the evaporator was then generated. The evaporator geometry was scaled down and simplified to reduce the simulation time. Due to restrictions in the software, the simulations were split into two parts - one for the flow of the refrigerant through the evaporator pipes and another for flow of air over the fins. The internal flow simulation was a steady state simulation consisting of the phase-change of the refrigerant after absorbing heat from the ambient. through the pipes and a transient simulation for the external flow over the fins. The internal flow consisted of multi-phase simulation of the evaporation of the refrigerant - propane - after absorbing heat through the pipe walls. The external flow involved the multi-phase simulation of ice being deposited from humid air on the surface of the fins. The inner surface of the evaporator pipes was used as a bridge, and surface profiles from the internal simulation would be used to transfer the boundary conditions to the other simulation. Results of the ice-film thickness over the fins were obtained and compared to the experimental value and found to be in reasonable agreement with each other, with scope for improvement in the future.

<div>In the 1970's, Arthur Ashkin developed a remarkable system called the ``optical tweezer'' which utilizes the radiation pressure of light to manipulate particles. Because of its non-invasive nature and controllability, optical tweezers have been widely adopted in biology, chemistry and physics. In this dissertation, two applications related to optical tweezers will be discussed. The first application is about the demonstration of multiple feedback controlled optical tweezers which let us conduct novel experiments which have not been performed before. For the second application, levitation of a silica nanodumbbell and cooling its motion in five degrees of freedom is executed.</div><div><br></div><div>To be more specific, the first chapter of the thesis focuses on an experiment using the feedback controlled optical tweezers in water. A well-known thought experiment called ``Feynman's ratchet and pawl'' is experimentally demonstrated. Feynman’s ratchet is a microscopic heat engine which can rectify the random thermal fluctuation of molecules to harness useful work. After Feynman proposed this system in the 1960’s, it has drawn a lot of interest. In this dissertation, we demonstrate a solvable model of Feynman’s ratchet using a silica nanoparticle inside a feedback controlled one dimensional optical trap. The idea and techniques to realize two separate thermal reservoirs and to keep them in contact with the ratchet is discussed in detail. Also, both experiment and simulation about the characteristics of our system as a heat engine are fully explored.</div><div><br></div><div>In the latter part of the dissertation, trapping silica nanodumbbell in vacuum and cooling its motion in five degrees of freedom is discussed. A levitated nanoparticle in vacuum is an extraordinary optomechanical system with an exceptionally high mechanical quality factor. Therefore, levitated particles are often utilized as a sensor in various research. Different from a levitated single nanosphere, which is only sensitive to force, a levitated nanodumbbell is sensitive to both force and torque. This is due to the asymmetry of the particle resulting it to have three rotational degrees of freedoms as well as three translational degrees of freedoms. In this dissertation, creating and levitating a silica nanodumbbell will be demonstrated. Active feedback cooling also known as cold damping will be employed to stabilize and cool the two torsional degrees of freedom of the particle along with the three center of mass DOF in vacuum. Additionally, both computational and experimental analysis is conducted on a levitated nanodumbbell which we call rotation-coupled torsional motion. The complex torsional motion can be fully explained with the effects of both thermal nonlinearity and rotational coupling. The new findings and knowledge of a levitated non-spherical particles leads us one step further towards levitated optomechanics with more complex particles.</div>

The standard approach to modelling mechanics of continuum based on bal- ances of mass, momentum, angular momentum and energy is a very powerful tool. However, there is no connection between that and the Hamiltonian mechanics, that superbly describes kinematics of isolated particles. Thus, the two topics are rather isolated. Nevertheless, there is another approach to continuum mechan- ics - a one, whose reversible part is based on Hamiltonian mechanics, while the irreversible is generated by a dissipation potential. This framework, called GENERIC, is thus an interesting bridge between con- tinuous and discrete systems. In this thesis, we present the GENERIC framework applied to a continuous body, derive the governing equations and compare them to the standard theory. Both analytical and numerical solutions to a decent range of model examples are presented and analysed.

Cubic carbides (titanium, tantalum, niobium, and zirconium carbides) can constitute a significant proportion of so-called cubic and cermet grades, where it is added to substitute a portion of tungsten carbide. It is thus critical to understand and be able to thermodynamically model the cubic carbide systems. In order to do this, the thermodynamic descriptions of lower order systems, such as the Ti-Cr-C system, need to be well studied. To approach this goal, an extensive literature survey of thermodynamic data and phase diagram information on the Ti-Cr-C system, the Ta-Cr-C system, the Nb-Cr-C system and the Zr-Cr-C is presented in this work. Experiments are performed in the Ti-Cr-C system using powder metallurgy and heat treatments. The solubility of Cr in FCC_TiC phase was experimentally measured at 1773K and compared with previous studies showing that the solubility reported earlier is too large. Thereafter, a re-optimization of FCC_TiC and liquid interaction parameters of the Ti-Cr-C system was performed taking into account the experimental data obtained both from previous studies and this work. The Gibbs energy descriptions of the Cr-carbide end members were compared between the one from the in-house database [SandvikTDB] and from other studies. With the new description, the solubility of Cr in FCC_TiC is better described.

This research enthusiastically highlights the bio-adsorption of methylene blue (MB) by local, poultry, NaOH and citric acid modified ubiquitous eggshell (LES, NLES, CLES, PES, NPES and CPES) adsorbents. The microstructures of these adsorbents indicated that they had some surface functional moieties that were responsible for the adsorption of MB. The Langmuir isotherm and PSO model best fit the experiment data. The largest Langmuir monolayer adsorption capacity qmax, was 242.47mg/g, with the largest MB initial concentration of 400mg/L. This was a clear indication and a confirmation that MB adsorption by the powdered eggshells was chemisorptive. Moreover, the values of F $F$, the thickness of the boundary layer/film were >0, showing that the rate limiting step for the adsorption process was controlled by more than one diffusion mechanism. The values of ΔG° for the adsorption of MB by the adsorbents indicated that the adsorption reactions were all non-feasible and non-spontaneous. The values for ΔS° (J/K/mol) for LES, NLES and CPES for the uptake of MB showed decrease in the chaos or degree of randomness of the adsorption reactions, and the reverse was the case for PES, NPES and CLES for the uptake of MB, which showed increase in the chaos or degree of randomness of the adsorption. The adsorption of MB by LES, NLES and CPES gave ΔH°(kJ/mol) values which were indicative of endothermic nature of the adsorption systems, and the reverse was the case for the uptake of MB by PES, NPES and CLES, which was indicative of the exothermic nature of the adsorption systems.

Dans les alliages 3d, les propriétés magnétiques des solutés peuvent être extrêmement sensibles aux environnements chimiques locaux, et avoir un impact crucial sur diverses propriétés thermodynamiques et cinétiques. Afin de comprendre les propriétés fondamentales de ces alliages, la première partie de ce travail est dédiée à l’étude ab-initio des effets de l’environnement chimique local sur l’état magnétique des solutés de Mn dans le Fe-Mn. Diverses configurations contenant du Mn, isolé ou sous forme d’amas, en présence de lacunes ou d’impuretés interstitielles sont étudiées et leur configuration magnétique de plus basse énergie est déterminée. Un modèle effectif d’interactions est paramétré à partir des données ab-initio afin d’étudier les propriétés des alliages Fe-Mn à température finie. Les propriétés clés sont identifiées et le modèle est validé à basse température en reproduisant les résultats ab-initio. L’utilisation de ce modèle couplé à des simulations Monte Carlo permet de simuler l’évolution chimique des alliages Fe-Mn en fonction de la température et de la concentration en Mn, tout en relaxant la structure magnétique en temps réel. Afin d’illustrer les possibles applications de ce modèle, diverses propriétés sont étudiées telles que la dépendance en concentration de la température de Curie ou encore l’évolution en température de l’énergie de mélange et de l’ordre atomique à courte distance. Puisque dans ces alliages la diffusion est en général régie par mécanisme lacunaire, nous proposons aussi un formalisme prenant en compte explicitement les effets de l’ordre magnétique local sur les propriétés des lacunes. Par simulations Monte Carlo de traceurs, cette approche prédit la dépendance en température de l’auto-diffusion dans le Fe en excellent accord avec les études expérimentales. La déviation de la loi d’Arrhénius proche de la température de Curie est directement prédite, ainsi que le changement de pente entre les régimes ferromagnétique et paramagnétique. La précision du modèle de Ruch, couramment utilisé dans la littérature, est discutée au vu des résultats obtenus. Enfin, cette approche est appliquée à la diffusion d’un soluté de Mn dans le Fe pur et comparée aux résultats expérimentaux. / In 3d alloys, magnetic properties of solutes can be extremely sensitive to local chemical environments and can have a crucial impact on various thermodynamic and kinetic properties. In order to properly understand the fundamental properties of these alloys, the first part of this work is dedicated to the study of the effects of local chemical environment on the magnetic state of Mn solutes in bcc Fe-Mn by means of Density Functional Theory. Namely, configurations containing Mn, being isolated or forming a cluster, and in the presence of vacancies or interstitial impurities are investigated and their lowest-energy magnetic configuration is determined. The ab-initio data produced are then used to parameterize an effective interaction model in order to study the properties of Fe-Mn alloys at finite temperature. The key features of Fe-Mn alloys are identified, and the model is validated at low temperature by reproducing ab-initio predictions. Using this model coupled to Monte Carlo simulations, we simulate the chemical evolution of Fe-Mn properties depending on temperature and Mn concentration while relaxing the magnetic structure on-the-fly. In order to illustrate the validity and the applicability of the model, we examine certain finite temperature properties of bcc Fe-Mn alloys such as the concentration dependence of the Curie temperature or the temperature evolution of the mixing energy and the atomic short-range order. Since diffusion in Fe and Fe-Mn alloys is generally ruled by vacancy-mechanism, we also propose a formalism to take explicitly into account the properties of vacancies in the interaction model and the effect of local magnetic state on these properties. Using tracer diffusion Monte Carlo simulations, this approach predicts the temperature dependence of self-diffusion in bcc Fe in excellent agreement with experimental results, including the deviation from Arrhenius law around the Curie temperature and the change of slope between the ferromagnetic and paramagnetic regimes. The accuracy of the widely used Ruch model is discussed in the light of the present results. Finally, we apply this approach to the diffusion of a Mn solute in bcc Fe and compare with experimental results.

This work is concentrated on the thermodynamic and kinetic aspects of water, alcohols, alkyl halides, ethers, and lactones bound and activated by the electrophilic [Cp'Ru(N0)] +2 and [Cp’Ru (NO)(CH3)] + centers (Cp' = cyclopentadienyl group). Counterions in these systems include OSO2CF3- (OTf-) and [(3, 5-(CF3)2C6H3)4B]- ([BAr4']-). The displacement of OTf- in Cp'Ru(N0) (0Tf)2 by H20 in dichloromethane is exothermic but entropically unfavorable due to the required reorganization of the solvent cage around released triflate ions. Thermodynamic parameters are also determined for OTf displacement by chloride and tetrahydrofuran (THF) using the 19F nuclear magnetic resonance (NMR) spectroscopy. The conversion of the [Cp’Ru (NO)(OH2)2] +2 to [Cp’Ru (NO)(μ-OH)} 2 +2 in aqueous solutions is characterized thermodynamically and kinetically by potentiometric and NMR methods. The results of the study of rhodium triflato complex trans- [Rh (CO)(PPh3)2(OTf)] show that OTf coordinates to the metal center in wet dichloromethane solutions, but the compound crystallizes as a water-coordinated triflate salt trans- [Rh (CO)(PPh3)2(OH2)] [OTf]. Thermodynamic parameters for alcohol (methanol, ethanol, isopropanol) binding to the Cp*Ru(N0) (0Tf)2 are determined from the 19F NMR spectroscopic data. The kinetics of the oxidation of alcohols to aldehydes or ketones via Ru (II) >>> Ru (0) redox process is studied by NMR methods. The results of the study support {3-hydrogen elimination mechanism, comprising one of the very few mechanistic investigations on reactions of this kind. Alkyl iodides are found to bind to the [Cp*Ru (NO)(CH3)] + fragment via displacement of a THF ligand in the presence of a BAr4 •-counterion, forming alkyl halide complexes that convert to [Cp’Ru (NO)(μ-I)]2+2. The mixed ruthenium-chromium complex [CpCr (NO)2(μ-I) (Ru (Cp’) (NOW is characterized as primarily a [Ru-I >> Cr] system as opposed to a [Ru << I-Cr] model. The complex [Cp*Ru (NO)(CH3) (THF)] is found to catalyze aerobic oxidation of THF to -y-butyrolactone. The new -y-butyrolactone ruthenium complex is isolated and characterized by X-ray methods in the solid state. The mechanism of catalytic oxidation is studied by 18O-labeled infrared spectroscopic methods. Radical decomposition of the intermediate hydroperoxy-tetrahydrofuran gives 1, 6-diol-diformate [CH(O)-(CH2)6-CH(O)]. The radical mechanism for the catalytic oxidation of THF is proposed.