Tesis sobre el tema "Condensation (process)"

The system of three differential equations describing the stochastic condensation process under quasiequilibrium equilibrium conditions is constructed taking into account the additive and multiplicative components. The phase diagram of the system states was constructed and analyzed. The domains of the existence of the condensation processes, disassembly of previously deposited material, and the complete evaporation were determined. The distribution density of the concentration of adsorbed atoms was defined. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34910

This PhD work has been dedicated to the improvement of the modelling of air condensers of both round tube and fins (RTPFs) and Minichannel technologies. The calculation platform employed is IMST-ART. This is a dedicated software for the design of refrigeration, air-conditioning and heat pump equipment following the vapor compression cycle. The model implemented in IMST-ART for condensers and evaporators is the combination of a segment-by-segment approach with the numerical method SEWTLE (Semi Explicit method for Wall Temperature Linked Equations) for the solution of the resulting system of equations. The target of the first part of this thesis was the comparative analysis of the empirical correlations aimed at the evaluation of the heat transfer coefficients and pressure drop in both the air and refrigerant sides of a condenser. The Literature review pointed out the presence of many studies concerning the condensation modelling. Therefore, after selecting the most interesting to compare, the first objective of this first part of the PhD became the identification of a suitable methodology for defining the best combination of correlations for the estimation of the thermo-hydraulic performance of the condensers. After an in-depth analysis of different possibilities, a well-defined methodology was identified as the best for the purpose. In the thesis, it was successfully applied to the identification of the best set of correlations for the heat transfer coefficients and friction factors for both the round-tube and minichannel condensers. The second part of the PhD was targeted to the improvement of the condensation modelling. In particular, the attention was focused on the analysis of the phenomena taking place at the beginning of the condensation process, when the superheated vapor finds the wall of the condenser being at a temperature lower than the refrigerant saturation temperature, i.e. convective condensation superheated vapor zone (CSH zone). It is well known that, in this zone, the condensation starts with some kind of droplet/thin film condensation on the walls. Afterwards, the bulk of the refrigerant flow reaches the saturation temperature and the condensation occurs at saturated conditions. Hence, the PhD thesis has been dedicated to the implementation in the general model for condensers (in IMST-ART software) of this CSH zone, which it was found to have an important effect on the prediction of the wall temperatures distribution in the tested air condensers. Two different numerical solutions were implemented and compared, i.e. Temperature and Enthalpy approaches, and validated against experimental results. Prediction results are very similar, thus the Enthalpy approach was selected because it required lower computational time. The final part of thesis was oriented towards the study of the effect of airflow maldistribution on the performance of air condensers. An innovative experimental methodology for generating and measuring any uneven air velocity profile at the inlet of a heat exchanger was first developed in a dedicated wind tunnel and then applied for the analysis of the performance degradation of one sample of condenser of each RTPFs and Minichannel technologies. Three different velocity profiles were produced and tested along a wide set of operating conditions, including different refrigerant charges and hence subcoolings. The experimental results showed that, although differences in wall temperature distribution were significant, the effect of air maldistribution on the performance of the two tested condensers was small. The improved model was validated against the experimental results and also showed little effect on condenser performance. Finally, the agreement between the results of the simulation and the experimental results was very satisfactory.
Este trabajo de doctorado se ha dedicado a la mejora del modelado de condensadores de aire, con tecnología de tubos y aletas o minicanales. La plataforma de software empleada es IMST-ART, que es un software dedicado a asistir el diseño de equipos de refrigeración, aire acondicionado y bomba de calor, basados en el ciclo de compresión de vapor. El modelo de IMST-ART para condensadores y evaporadores se basa en una aproximación segmento a segmento combinada con el método numérico SEWTLE (Semi Explicit method for Wall Temperature Linked Equations) para la solución del sistema de ecuaciones resultante. El objetivo de la primera parte de esta tesis fue el análisis comparativo de las correlaciones empíricas destinadas a evaluar los coeficientes de transferencia de calor y la caída de presión para condensadores de aire, tanto para el lado del aire como para el del refrigerante. La revisión de la Literatura mostró la existencia de numerosos estudios sobre el modelado de la condensación en este tipo de intercambiadores. Por lo tanto, después de la selección de las correlaciones más interesantes a comparar, el primer objetivo de esta primera parte de la tesis resultó el encontrar la metodología más adecuada para la identificación de cuáles eran las correlaciones que mejor estimaban el comportamiento termo-hidráulico de los condensadores. Después de un análisis en profundidad de diferentes posibilidades, se encontró la metodología claramente más adecuada y se pasó a aplicarla a la identificación del mejor conjunto de correlaciones para los coeficientes de transferencia de calor y factores de fricción para condensadores de aire. La segunda parte del doctorado se dirigió a la mejora del modelado del comienzo del proceso de condensación cuando el vapor sobrecalentado encuentra la pared del condensador a una temperatura que está por debajo de la temperatura de saturación del refrigerante en lo que se puede denominar como condensación convectiva en la zona de vapor sobrecalentado (zona CSH). Es bien sabido que la condensación comienza en esta zona con algún tipo de condensación de gotas/película delgada sobre las paredes antes de que el núcleo del flujo de refrigerante alcance la temperatura de saturación y la condensación se produzca en condiciones saturadas. La segunda parte del doctorado se ha dedicado a la implementación en el modelo general de condensadores (en el software IMST-ART) de esta zona CSH, que se encontró que tenía un efecto importante en la predicción de la distribución de las temperaturas de la pared en los condensadores de aire ensayados. Se implementaron y compararon dos soluciones numéricas diferentes, denominados aproximación de temperatura y aproximación de entalpía respectivamente, y se validaron por comparación con resultados experimentales. La predicción resultó ser muy similar con ambas aproximaciones por lo que finalmente se seleccionó la aproximación de entalpía por ser considerablemente más rápida. La parte final de la tesis se orientó hacia el estudio del efecto de la mala distribución del flujo de aire en el rendimiento de los condensadores de aire. Para este fin se desarrolló una metodología experimental innovadora capaz de generar y medir cualquier perfil de velocidad de aire no uniforme a la entrada de un intercambiador de calor. El desarrollo se llevó a cabo primero en un túnel de viento específicamente dedicado a este propósito y luego se aplicó para el análisis de la degradación de las prestaciones de dos muestras de condensador de cada una de las tecnologías estudiades: RTPFs y Minicanal. Mediante la metodología desarrollado se generaron tres perfiles de velocidad diferentes que se ensayaron a lo largo de un amplio conjunto de condiciones de funcionamiento, incluyendo diferentes cargas de refrigerante y, por tanto, grados de subenfriamiento en el refrigerante. Los resultados experimentales mostraron que el efecto de la mala distrib
Aquest treball de doctorat s'ha dedicat a la millora de la modelització de condensadors d'aire, amb tecnologia de tubs i aletes o minicanals. La plataforma de software emprada és IMST-ART, que és un software dedicat a assistir el disseny d'equips de refrigeració, aire condicionat i bomba de calor, basats en el cicle de compressió de vapor. El model de IMST-ART per condensadors i evaporadors es basa en una aproximació segment a segment combinada amb el mètode numèric SEWTLE (Semi Explicit method for Wall Temperature Linked Equations) per a la solució del sistema d'equacions resultant. L'objectiu de la primera part d'aquesta tesi va ser l'anàlisi comparativa de les correlacions empíriques destinades a avaluar els coeficients de transferència de calor i la caiguda de pressió per condensadors d'aire, tant per al costat de l'aire com per al del refrigerant. La revisió de la Literatura va mostrar l'existència de nombrosos estudis sobre la modelització de la condensació en aquest tipus d'intercanviadors. Per tant, després de la selecció de les correlacions més interessants a comparar, el primer objectiu d'aquesta primera part de la tesi va resultar el trobar la metodologia més adequada per a la identificació de quines eren les correlacions que millor estimaven el comportament termo-hidràulic dels condensadors. Després d'una anàlisi en profunditat de diferents possibilitats, es va trobar la metodologia clarament més adequada i es va passar a aplicar-la a la identificació del millor conjunt de correlacions per als coeficients de transferència de calor i factors de fricció per condensadors d'aire. La segona part del doctorat es va dirigir a la millora de la modelització del començament del procés de condensació quan el vapor sobreescalfat troba la paret del condensador a una temperatura que està per sota de la temperatura de saturació del refrigerant, en el que es pot denominar com condensació convectiva a la zona de vapor sobreescalfat (zona CSH). És ben sabut que la condensació comença en aquesta zona amb algun tipus de condensació de gotes/pel·lícula sobre les parets abans que el nucli del flux de refrigerant arribi a la temperatura de saturació i la condensació es produeixi en condicions saturades. La segona part del doctorat s'ha dedicat a la implementació en el model general de condensadors (en el programari IMST-ART) d'aquesta zona CSH, que es va trobar que tenia un efecte important en la predicció de la distribució de les temperatures de la paret en els condensadors d'aire assajats. Es van implementar i van comparar dues solucions numèriques diferents, denominades aproximació de temperatura i aproximació d'entalpia respectivament, i es van validar per comparació amb resultats experimentals. La predicció va resultar ser molt semblant amb les dues aproximacions pel que finalment es va seleccionar l'aproximació d'entalpia per ser considerablement més ràpida. La part final de la tesi es va orientar cap a l'estudi de l'efecte de la mala distribució del flux d'aire en el rendiment dels condensadors d'aire. Amb aquesta finalitat es va desenvolupar una metodologia experimental innovadora capaç de generar i mesurar qualsevol perfil de velocitat d'aire no uniforme a l'entrada d'un intercanviador de calor. El desenvolupament es va dur a terme primer en un túnel de vent específicament dedicat a aquest propòsit i després es va aplicar per a l'anàlisi de la degradació de les prestacions de dues mostres de condensador de cadascuna de les tecnologies estudiades: RTPFs i Minicanal. Mitjançant la metodologia desenvolupada es van generar tres perfils de velocitat diferents que es van assajar al llarg d'un ampli conjunt de condicions de funcionament, incloent càrregues diferents de refrigerant i, per tant, graus de subrefredament en el refrigerant. Els resultats experimentals van mostrar que l'efecte de la mala distribució de l'aire en les prestacions dels dos condensadors provats va
Pisano, A. (2017). Analysis of the condensation process and air maldistribution in finned tube and minichannel condensers [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86182
TESIS

The aim of the present thesis is to model the conversion process of the fast pyrolysis vapours into liquid bio-oil in liquid collection systems. The study focuses on the two major types of condensation systems namely the indirect contact condensers and the direct contact condensers (quenching columns). In the first part of the research, the hydrodynamic and heat transfer characteristics of a bench scale quenching column are presented by conducting numerical simulations based on the immiscible Eulerian-Eulerian model. The simulations are compared with experimental observations on flooding phenomena and various design variants are proposed for their elimination. In the second part, a multiphase multi-component model, with the condensable vapours and non-condensable gases as the gaseous phase and the condensed bio-oil as the liquid phase, has been developed. Species transport modelling has been used to capture the detailed physical phenomena of 11 major compounds present in the pyrolysis vapours. The development of the condensation model relies on the saturation pressures of the individual compounds computed based on the corresponding state correlations. In the final part, detailed information is provided on the vapour phase change dynamics implemented on a disc and donut quenching column design obtained from the first part. The study investigates the effect of the different numbers of disc and donut pairs on the condensation performance of the column. The numerical simulations showed that different number of stages can significantly affect the final bio-oil composition. It is shown that heavy molecular weight compounds, condense rapidly even with a low number of stages, whereas an increased number of stages is needed to completely capture the heavier acidic fractions. The modelling results are in good agreement with data published in the existing literature.

Zn-55%Al-1.5%Si coated steel strip is manufactured by the continuous hot dipping process. An important difference in the processing of Zn-55%Al-1.5%Si coated steel when compared with galvanised steel is the higher temperature of the molten alloy bath –600ºC for Zn-55%Al-1.5%Si coatings versus 450ºC for galvanised. This increase in temperature leads to an accelerated rate of evaporation of zinc into the pretreatment furnace, leading in turn to various processing difficulties. Zinc vapour in the pre-treatment furnace has long been implicated with defects known within the industry as pinholes and bare patches - uncoated areas where wetting does not occur between the strip and the molten alloy. Despite the association with zinc vapour, the exact mechanisms of pinhole and bare patch formation have not been clearly established. One possible mechanism of pinhole and bare patch formation is the direct reaction of zinc vapour with the strip surface. It has been suggested by industry experts that zinc vapour could condense on the strip, leaving a deposit that prevents wetting by molten Zn-55%Al-1.5%Si alloy. It remains that little is understood of the fundamental nature of the interaction between zinc vapour and a steel substrate. The purpose of this research was to examine the rates and mechanisms of zinc vapour condensation on clean and oxidised steel substrates. Such information is essential for understanding the reactions that occur in the metal coating line furnace. It is intended that this research will strengthen the fundamental knowledge base upon which a solution to the problem can be developed. The experimental work conducted in this study was centred on condensing zinc vapour onto substrates under specific gaseous atmospheres at atmospheric pressure. A major part of the work involved the development of a technique for depositing zinc vapour onto a steel substrate and the design and construction of an experimental apparatus. Preliminary studies were undertaken to define the design criteria for an apparatus in which the rate of condensation of zinc vapour could be measured accurately and the interaction between zinc vapour and clean and oxidised steel substrates could be examined. In this probing exercise, modifications were made to a proven design of an apparatus designed to measure evaporation rates of metals in inert gas atmospheres was used. The preliminary experiments provided a wealth of essential knowledge required to design an experimental facility in which it was possible to accurately measure the rate of condensation of zinc vapour and to study the interaction between zinc vapour and the steel substrate, as well as their potential chemical reactions. This new apparatus was specifically developed for a quantitative assessment of zinc vapour deposition, and allowed the substrate and zinc vapour to be heated in independent, but interconnecting chambers. The exposure of the substrate to the zinc vapour could be controlled with precision, and it was possible to not only measure the zinc vapour condensation rates, but also to assess the effect of using oxidising and reducing gasses during preheating of the substrate. Under conditions of high undercooling, zinc vapour deposited by the island plus continuous thin film mode, while at higher substrate temperatures, close to that expected in the industrial process, the zinc deposited more slowly, and zinc islands did not form on the substrate within the first 60 seconds of exposure. Deposition of zinc vapour on an oxidised substrate occurred at a much higher rate than on a clean steel substrate. This increase in deposition rate has been attributed to a direct reaction occurring between the zinc vapour and the iron oxide without the formation of any liquid condensate. The reaction is: Fe3O4(s) + 4Zn(v) ↔ 4ZnO(s) + 3Fe(s) This reaction will proceed to the right under sufficiently high partial pressures of zinc vapour, and at substrate temperatures both above and below the saturation temperature of the zinc vapour. It was observed that under sufficiently low partial pressures of zinc vapour, the above reaction is driven to the left. Zinc oxide has a determining influence on the wetting of the strip by the molten alloy. Immersion tests, wherein substrates deposited with zinc vapour were dipped into molten Zn-55%Al-1.5%Si alloy, were carried out to examine the effect of various zinc vapour reactions on the quality of the coatings. Deposition of zinc vapour on both clean and oxidised steel surfaces had a detrimental effect on the coating quality. In cases where zinc was deposited onto a clean steel substrate prior to immersion in the coating alloy, pinholes resulted, while zinc vapour deposition on an oxidised surface prior to immersion led to large scale uncoated areas.

The Ginibre gas is a Poisson point process dened on a space of loops related to the Feynman-Kac representation of the ideal Bose gas. Here we study thermodynamic limits of dierent ensembles via Martin-Dynkin boundary technique and show, in which way innitely long loops occur. This effect is the so-called Bose-Einstein condensation.

L'objectif de ce travail est d'analyser théoriquement et expérimentalement la condensation des espèces inorganiques dans une installation de gazéification de la biomasse. Lors de la gazéification de la biomasse, des espèces inorganiques sont volatilisées et se condensent lors du refroidissement du gaz de synthèse. Ces espèces sont problématiques pour le procédé et doivent être éliminées avant la synthèse des biocarburants. Une étude thermodynamique a tout d'abord précisé la nature et la répartition des espèces inorganiques qui sont volatilisées lors de la gazéification ainsi que des espèces qui se condensent lors du refroidissement. Un modèle de condensation des aérosols issus de la gazéification de la biomasse a ensuite été construit à partir de d'une description mathématique des différents phénomènes mis en jeu (nucléation, croissance, agglomération et dépôts). Parallèlement un dispositif expérimental (ANACONDA) a été mis au point, construit et qualifié. Ce dispositif permet d'analyser la condensation d'une vapeur de KCl dans un écoulement pouvant comporter des particules de carbone se refroidissant à une vitesse de 1000 K/s. Les résultats expérimentaux obtenus ont mis en évidence une nucléation du KCl lors d'un refroidissement à 1000 K/s, la condensation de KCl sur les particules de carbone ainsi que le dépôt de KCl et des particules sur les parois. La condensation de KCl provoque une augmentation du diamètre aérodynamique des particules de carbone. La présence de particules dans l'écoulement permet de diminuer les dépôts de KCl aux parois de 25% à 40%. La comparaison de calculs simulant les expériences avec les données expérimentales a permis de quantifier les différents phénomènes et de valider le modèle. Enfin, le modèle a été utilisé afin de proposer des solutions pour limiter les dépôts de KCl aux parois des échangeurs dans une installation industrielle de gazéification de la biomasse.

In this essay, the novel Beloved, by Toni Morrison is observed using a working psychoanalytical approach. Story is observed as an important factor in engaging the reader on a personal level with the experience of trauma. By surveying Morrison’s use of imagery and language, this essay will examine how Morrison employs literary methods that imitate the psychological processes regarding how trauma is communicated to the waking state from the unconscious. The resulting testimony of the novel that arises as the result of these processes is also observed. This essay concludes that Morrison’s use of these literary methods functions to obligate the reader to involve themselves in the process of trauma and its resolution.

Les limites d'échelle de grands arbres aléatoires jouent un rôle central dans cette thèse.Nous nous intéressons plus spécifiquement au comportement asymptotique de plusieurs fonctions codant des arbres de Galton-Watson conditionnés. Nous envisageons plusieurs types de conditionnements faisant intervenir différentes quantités telles que le nombre total de sommets ou le nombre total de feuilles, avec des lois de reproductions différentes.Lorsque la loi de reproduction est critique et appartient au domaine d'attraction d'uneloi stable, un phénomène d'universalité se produit : ces arbres ressemblent à un même arbre aléatoire continu, l'arbre de Lévy stable. En revanche, lorsque la criticalité est brisée, la communauté de physique théorique a remarqué que des phénomènes de condensation peuvent survenir, ce qui signifie qu'avec grande probabilité, un sommet de l'arbre a un degré macroscopique comparable à la taille totale de l'arbre. Une partie de cette thèse consiste à mieux comprendre ce phénomène de condensation. Finalement, nous étudions des configurations non croisées aléatoires, obtenues à partir d'un polygône régulier en traçant des diagonales qui ne s'intersectent pas intérieurement, et remarquons qu'elles sont étroitement reliées à des arbres de Galton-Watson conditionnés à avoir un nombre de feuilles fixé. En particulier, ce lien jette un nouveau pont entre les dissections uniformes et les arbres de Galton-Watson, ce qui permet d'obtenir d'intéressantes conséquences de nature combinatoire.

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The aim of this research was to investigate the knowledge mobilized by those students who have studied Integral, a subject that permeates a major part of the Integral and Differential Calculus (IDC) course and is a source of difficulties for the students. The goal was to analyze the explicit knowledge of those who have studied this concept in a regular IDC course in terms of the integration techniques as well as the meaning and the concept utilization. It has also been researched whether this knowledge reflected operational and structural conceptions in the sense applied by Anna Sfard (1991), whose theory this paper is based on. In her studies, the author postulates that abstract notions are conceivable in two completely different ways: structurally (as objects) and operationally (as processes). As an investigation means, it has been used a questionnaire containing nine questions and applied to two groups of a private school s math course in São Paulo city. One of the groups was constituted by students who have recently studied the notion of Integral, and the other group by students who went through the same studies one year before. In terms of the first group, the conclusion drawn up was that the students have incurred in several kinds of operational calculus mistakes, also the processes involving integral notion showed up but only sometimes, indicating a clear structural conception failure. These characteristics were not observed in the second group. It has been noticed that all researched students apparently had mobilized the structural concept considering they have applied the mathematical object to determine the area of even spaces in the function graph, but when facing those circumstances in which they had to reason to be able to apply the concept as an object they did not have enough assurance in terms of structural conception, and tried to take refuge in the algebra processes
Esta pesquisa buscou investigar os conhecimentos mobilizados por alunos, que estudaram o conceito de Integral, que permeia grande parte da disciplina Cálculo Diferencial e Integral (CDI) e que é fonte de dificuldades para os alunos. Buscouse analisar os conhecimentos explicitados por alunos que estudaram o conceito num curso regular de CDI, tanto no aspecto das técnicas de integração como no significado e na aplicação do conceito. Pesquisou-se, igualmente, se estes conhecimentos refletiam concepções operacionais e estruturais no sentido atribuído por Anna Sfard (1991), que fundamentou teoricamente este estudo. Em seu estudo, a autora postula que noções abstratas podem ser concebidas e duas maneiras fundamentalmente diferentes: estruturalmente (como objeto) e operacionalmente (como processo). Como instrumento de investigação foi utilizado um questionário com nove questões que foi aplicado a dois grupos de alunos do Curso de Matemática de uma instituição particular de São Paulo. Um deles constituídos por alunos que haviam estudado recentemente a noção de Integral e o outro, por estudantes que o fizera há cerca de um ano. Concluiu-se que, no caso do primeiro grupo, os alunos, além de terem apresentado variados tipos de equívocos em cálculos operatórios, os processos que envolvem a noção integral ora manifestam concebidos ora não, concorrendo para o prejuízo da concepção estrutural, o que não ocorreu no segundo grupo. Observou-se que a totalidade dos alunos pesquisados, aparentemente mobilizara a concepção estrutural, uma vez que aplicaram o objeto matemático para determinar a área de regiões planas sob o gráfico de funções, mas quando colocados numa situação particular em que se exigia uma reflexão para o emprego do conceito como objeto, eles não exibiram suficiente segurança em sua concepção estrutural, procurando refúgio em processos algébricos

The diploma thesis deals with the thermal-humidity stress of the wooden wall. The work is focused on the connection of the wall to the base structure of the building. Three details were chosen. The work was focused on detail with the most common structure of an external wall used in the Czech Republic on the composition with a supporting structure made of KVH columns, which are filled with mineral insulation. This construction is covered with plate elements. The insulation from the exterior is made of ETICS with expanded polystyrene thermal insulation. This detail was assessed in the software. To compare the results calculated by real-time software, an experimental model was made, which was subjected to experimental measurements. Part of the diploma thesis is a comparison of detail stress under different boundary design conditions, with or without anchoring.

Le procédé de fusion sélective par laser (SLM) d’un lit de poudre métallique, est un procédé de fabrication additive qui permet de fabriquer des pièces de forme complexe directement à partir d’un fichier CAO en passant par la fusion totale de couches de poudre déposées successivement. Au cours du procédé SLM l’apport d’énergie du laser à la cible engendre de nombreux cycles thermiques: fusion – vaporisation – solidification. Dans ce contexte, cette thèse a pour double objectif :1) une meilleure caractérisation et compréhension des phénomènes qui se produisent lors de l’interaction du faisceau laser avec la poudre et le bain de métal fondu à l’aide d’essais et 2) le développement d’un modèle numérique prenant en compte les phénomènes de fusion et de vaporisation de la matière ainsi que à la présence du gaz environnant à l’intérieur de la chambre de fabrication.Dans un premier temps, en considérant des géométries simples (cordons et surfaces) en acier inoxydable 316L, on a étudié l’interaction faisceau laser - lit de poudre / bain liquide métallique par différentes méthodes de diagnostics (spectrométrie, calorimètre, …) pour comprendre la nature et le rôle de la vapeur métallique générée au cours du procédé. Les résultats ont montré que cette vapeur est sans effet sur la transmission de l’énergie du laser à la matière au cours du procédé SLM. Par contre, elle conduit à la formation de condensats et peut aussi entrainer des gouttelettes de métal fondu.Ces analyses ont permis, dans un second temps, de développer un modèle numérique qui a pour objectif principal de caractériser l’influence de la pression du milieu environnant sur le processus de fusion du lit de poudre par le faisceau laser. Des paramètres caractérisant l’évolution des propriétés physiques du matériau et du milieu gazeux en fonction de la température et de la pression ont été intégrés dans les bases de données du modèle. Ces paramètres physiques du matériau ont été déterminés à partir de la littérature et d’autres ont été obtenus empiriquement à l’aide de mesures expérimentales spécifiques.Ce modèle numérique a été utilisé pour traiter le sujet principal de la thèse, à savoir celui de l’effet de la pression. Le modèle a permis de préciser les phénomènes physiques inhérents à la variation de la pression. Des manipulations expérimentales ont permis de vérifier la pertinence des données du modèle numérique proposé
The selective laser melting process (SLM) of a metallic powder bed is an innovative process that allows the manufacturing of complex shape parts directly from a CAD file via a complete melting of powder layers deposited successively. During the SLM process, the high laser energy density creates many thermal cycles: melting - vaporization - solidification.The purpose of this work was: 1) to better characterize and understand experimentally the phenomena that occur during the laser beam - powder / molten metal pool interaction and 2) to develop a numerical model taking into account the phenomena of melting and vaporizing of the material and the presence of the surrounding gas in the build chamber.In a first time, considering simple geometries (tracks and surfaces) and 316L stainless steel as material, we studied the interaction between the laser beam, the powder bed and the liquid metal pool using several experimental techniques (spectrometry, calorimetry, ...) in order to understand the nature and the role of the metal vapor generated during the process. The results showed that the vapor has no effect on the transmission of the laser beam energy to the material during the SLM process. Meanwhile it leads to the deposition of condensed vapor and also drag some molten metal droplets.In a second time a numerical model was developed to determine the influence of the pressure of the surrounding environment on the melting process of a powder bed by a laser beam. Parameters characterizing the evolution of the physical properties of the material and of the gaseous medium according to the temperature and pressure were incorporated into the model database. Some material parameters were determined from the literature and others were obtained empirically using specific experimental measurements.Finally, this numerical model, complementing experimental results, was used to treat the main subject of the thesis which is the effect of the surrounding pressure on the SLM process. The model helped to clarify the physical phenomena provided by the change in the pressure level and its validity was checked through experimental measurements

Ce memoire est consacre a la conception et la mise au point du controle in-situ de la croissance de lasers a cavite verticale et a emission surfacique (vcsel). Les structures laser sont elaborees par epitaxie par jets moleculaires a source gazeuse et realisees par l'empilement de couches minces a base de semi-conducteurs gaas/algaas. Leur longueur d'onde d'emission va dependre directement des caracteristiques optiques des couches deposees. Une etude theorique est d'abord menee sur la conception de ces structures. Nous commencons par determiner les constantes optiques des materiaux qui les composent en portant une attention particuliere a l'effet excitonique dans les puits quantiques. L'utilisation du formalisme matriciel nous permet de decrire la propagation des ondes electromagnetiques dans n'importe quelle structure multicouche. Nous pouvons alors simuler le comportement optique de n'importe quel empilement de couches minces, en particulier des miroirs de bragg et des microcavites que constituent ces lasers. Un chapitre est ensuite consacre a l'elaboration des vcsel. Une description precise des contraintes imposees par la machine et de l'optimisation des conditions de croissance est presentee. Cette etude fait apparaitre la necessite de disposer d'un moyen de controle in-situ des couches realisees. Le dernier chapitre presente la mise au point de la methode de controle. La croissance est interrompue apres que le miroir inferieur et la cavite aient ete epitaxies. A partir d'un spectre de reflectivite realise sur cette structure incomplete, un algorithme de type recuit simule nous permet de determiner precisement les flux et par consequent les epaisseurs et les compositions des couches de la premiere partie de la croissance. La correction de la structure est obtenue par une modification des temps d'epitaxie du miroir superieur. L'utilisation de cette technique nous a permis de fixer la longueur d'onde du pic fabry-perot de la structure complete avec une precision de 0,15%

Les réactions de métathèse sont des méthodes performantes pour la création de doubles liaisons carbone-carbone et leurs popularités s'expliquent par l'accessibilité des catalyseurs nécessaires à celles-ci et par la facilité de mise en oeuvre de ces réactions. Elles ont par ailleurs trouvé de nombreuses applications dans la synthèse de molécules naturelles.Les aurisides A et B sont des molécules naturelles d'origine marine isolées du lièvre des mers Dolabella Auricularia en 1996. Ces macrolides présentent une activité cytotoxique intéressante contre des lignées de cellules cancéreuses HeLaS3 avec des valeurs d'IC50 de 0,17 et 1,2 μg/mLrespectivement.Nous avons dans un premier temps développé une voie d'accès au fragment C1-C9 des composés naturels en se basant sur la réaction de métathèse croisée des oléfines. Une étude sur le mode formation de la structure macrocylique par un processus séquentiel impliquant une réaction demétathèse cyclisante et une cétalisation transannulaire a ensuite été conduite sur des composés modèles permettant l'obtention de macrolactones analogues. Cette méthodologie a ensuite été appliquée à la synthèse stéréocontrôlée du squelette carboné des aurisides seulement dépourvu de sa chaîne latérale attaché sur l'atome de carbone C13.Enfin la réaction de métathèse croisée a également été exploitée dans un processus tandem avec celle d'hydrogénation pour la synthèse énantiosélective du 6-hydroxydodécanoate de pentadécyle,composant principal de l'huile essentiel Ylang-Ylang, et qui est également utilisé en médecine traditionnelle contre le choléra.

O dióxido de carbono no estado supercrítico (CO2-SC) tem despertado considerável interesse nos últimos anos como um novo solvente para reações orgânicas. Nesta tese foi investigada a influência do uso de CO2 supercrítico, associado ou não a líquidos iônicos ou cossolventes, como solvente em reações químicas visando à obtenção de precursores quirais. Foram estudadas as reações de condensação Aldólica, de Morita-Baylis-Hillman (MBH) e do tipo adição de Michael, empregando Organocatálise quando conveniente, isto é, catalisadores provenientes de aminoácidos e ácidos carboxílicos. As reações de MBH foram otimizadas através de um planejamento experimental e sua condição ótima se deu a 70°C, 110 bar, com 6 equivalentes de H2O, tempo reacional de 2h30 min e sem a presença de liquido iônico, tendo um rendimento de 84,6%. Para as condensações aldólicas os melhores resultados com acetona e p-nitrobenzaldeido como materiais de partida foram obtidos a 150 bar e 40°C, com a presença de liquido iônico, em 2 horas de tempo reacional com um rendimento de 54,0% e um excesso enantiomérico de 79,0% utilizando o catalisador (2S,4R)-4-(terc-butildimetilsililoxi)pirrolidina-2-ácido carboxílico. Com ciclohexanona como material de partida foram obtidos a 150 bar e 40°C com a presença de um doador de prótons (resina de troca iônica) em 2 horas de tempo reacional com um rendimento de 70,9% e um excesso enantiomérico de 91,2%, utilizando o catalisador (2S,4R)-4-(terc-butildimetilsililoxi)pirrolidina-2-ácido carboxílico. Outros aldeídos e cetonas utilizados como materiais de partida apresentaram rendimentos menores. Estudos de comportamento de fases foram feitos para os materiais de partida, catalisadores e produtos da reação de condensação Aldólica. Os melhores rendimentos foram obtidos em situações em que os materiais de partida e os catalisadores eram solúveis na fase supercrítica, mas os produtos não, formando uma segunda fase.
Supercritical carbon dioxide (sc-CO2) has attracted considerable interest in the last years as a new solvent for organic reactions. In this thesis, the influence of supercritical CO2 use, associated or not to ionic liquids or cosolvents, as a solvent for chemical reactions aiming at the synthesis of chiral precursors was studied. Aldol condensation, Morita-Baylis-Hillman (MBH) and Michael addition reactions were studied, employing organocatalysis when it was convenient, i.e., catalysts derived from aminoacids or carboxylic acids. MBH reactions were optimized through experimental design, resulting in a maximum yield of 84.6% for the optimal condition at 70°C, 110 bar, and 6 equivalents of H2O, reaction time of 2h30 min and the absence of ionic liquids. For the Aldol condensation reactions employing acetone and p-nitrobenzaldehyde, a maximum yield of 54.0%, with an enantiomeric excess of 79.0% was obtained at 150 bar, 40°C, 2h reaction time, in the presence of ionic liquid, using the catalyst (2S,4R)-4-(terc-butyldimethylsililoxy)pirrolidine-2-carboxylic acid. The yields were significantly lower for other aldehydes and ketones. Yields for Michael addition reactions were very low and their study was discontinued. Phase behavior studies were performed with starting materials, catalysts and products for the Aldol condensation reactions. The best yields were obtained for situations where the starting materials and catalysts were soluble in the supercritical phase and the products were not, forming a second phase.

L'hydrolyse-condensation de l'isopropoxyde de titane sous conditions neutres a ete etudiee par diffusion de la lumiere. Il a ete montre que des particules de taille nanometrique sont presentes pendant toute la periode d'induction du processus, le rayon des particules variant de 2 a 4 nanometres. L'influence des concentrations des reactifs sur la cinetique de croissance a ete analysee. L'analyse de la variation de l'intensite diffusee en fonction du rayon moyen a permis d'obtenir la dimension fractale des particules qui est egale a 1,4. Une methode d'analyse de la polydispersite a ete developpee. Le caractere de decroissance de la fonction de distribution de taille des particules en puissance de leur rayon pour les grandes tailles de particules est caracteristiques de l'agregation limitee par reaction (alr). L'analyse des donnees cinetiques a permis de montrer que pendant la periode d'induction le processus consiste en deux etapes principales. La premiere etape est l'hydrolyse rapide initiale et la formation de particules primaires de rayon egal a 2 nanometres. La deuxieme etape est l'hydrolyse supplementaire et la condensation qui gouvernent la croissance des particules primaires. L'introduction du taux d'hydrolyse initiale a permis d'obtenir une representation universelle pour la variation de la vitesse de croissance en fonction des concentrations des reactifs. Le modele alr generalise avec un cfficient de collage variant en fonction de la concentration de l'eau est propose pour expliquer la cinetique de croissance. Cette nouvelle approche pour expliquer le phenomene du temps d'induction a ete proposee pour remplacer l'hypothese d'accumulation des monomeres hydrolysees pendant cette periode. La precipitation des oxopolymeres est expliquee par l'augmentation de la sursaturation causee par la diminution de la solubilite des oxopolymeres au cours de leur croissance.

There exist large number of techniques for the preparation of nanostructured materials. Among them the preparation of nanopowders by gas/vapour condensation is a popular one. Because of very high level of surface to volume ratio, powders of metals which may or may not be reactive in the bulk form undergo vigorous oxidation. Oxidation once initiated continues in an auto catalytic fashion leading to a rise in temperature further increasing the oxidation rate. Therefore, the nanopowders are consolidated in situ under high vacuum. Alternatively a thin passivating oxide layer of few nm can be produced by slow exposure to air. Such powders lend themselves to be handled in further processing in ambient atmosphere. The main objective of the present research is to understand the various scientific and technological issues involved in preparing such passivated nanopowders by levitational gas condensation (LGC) technique, a relatively less explored vapour condensation process and their subsequent consolidation by the powder metallurgical route of compaction and sintering. The nanopowders systems studied are Fe and Fe-Cu (4 wt. %Cu). In chapter 1 a brief review of the gas condensation process and the consolidation behavior of nanopowders produced by this method were carried out. Existing knowledge on various topics relevant for the present study like formation of nanoparticles, agglomeration during gas condensation, physical, structural and chemical nature of the passive layer formed during passivation, compaction and sintering behaviour of this passivated nanopowders were discussed. Chapter 2 details the synthesis of Fe nanopowders by levitational gas condensation process and its physical and structural characteristics. The nanopowders in the as synthesized condition showed extremely low packing density due to loosely packed weakly interlocked agglomerates. The nanoparticles manifest as three dimensional reticulated spongy structure composed of chains of these nanoparticles. Heat transfer calculation carried out to determine the particle temperature at different distance from the levitating drop indicates that the nanoparticles can be ferromagnetic at a distance of less than 2 mm away from the levitation drop and hence the magnetic nature of the materials plays an important role in the formation of nanoparticle chains and spongy agglomerates. Passivation of the nanopowders by slow exposure to air produces 3-4 nm thick oxide layer (Fe3O4) over α-Fe and the volume of these oxides was around 45%. The 3rd chapter presents and discusses the results of Fe-Cu alloy nanopowder synthesized by levitating gas condensation process. While synthesis of elemental nanopowders by gas condensation is straight forward as the operating conditions only influence the particle size, alloys require careful control of the levitating drop composition. Although initially we start the process with levitated drop of required composition, the vapour generated will be richer in more volatile element (Cu in our case). Thus the composition of the levitated drop progressively becomes deficient in Cu which in turn reduces Cu in the vapour. Composition of the drop can be stabilised by continuous feeding of the alloy of required composition that can be estimated from the knowledge of equilibrium relation. To establish the equilibrium relationship between composition of the liquid and vapour in evaporation and condensation, phase diagram in the liquid and vapour region was calculated and was validated by determining composition of the drops. Good agreement between the drop composition and the composition predicted by the phase diagram were observed. Various physical, chemical and structural properties of the Fe-Cu nanopowders are characterized in detail using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and thermogravimetry (TG) analysis. The overall chemical composition of the Fe-Cu alloy nanopowders and of the individual agglomerates is same as the composition of feed materials used. However, Cu was found to segregate to the surface of the nanopowders which is attributed to minimization of surface energy with Cu at the surface. The total weight loss observed in TG in flowing hydrogen indicates that the surface passive layer of Fe-Cu appears to be very thin compared to Fe. The consolidation behaviour of both Fe and Fe-Cu nanopowders was studied by both conventional and spark plasma sintering (SPS) and are discussed in chapter 4. The as collected nanopowders from the apparatus have extremely low apparent density. The powders were further subjected to soft milling in a ball mill under ethanol to disentangle the agglomerates there by improving the pack density. A tenfold improvement was achieved thus making it suitable for consolidation. Uniaxial compaction of these powders for conventional sintering at pressure below 200 MPa yielded compacts free from defects. However, at higher pressure the compacts cracks and delaminates during ejection stage. Analysis of the compaction curves helped us to understand various processes involved during compaction as well as providing explanation for lower green density of Fe-Cu powder compared to Fe. Conventional sintering of the nanopowders compacts were carried out in the flowing hydrogen atmosphere in a laboratory vacuum furnace over wide range of temperatures. Instrumented sintering experiments were also carried out in a dilatometer under hydrogen atmosphere to evaluate shrinkage rate at different temperatures. SPS were carried out under 10 Pa vacuum at a compaction pressure of 250 MPa in WC-Co die cavity. The stability, density and residual oxygen content of the sintered compacts were quantified. Detailed microstuctural analysis of the sintered samples were also carried out using optical microscopy, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy and quantitative composition analysis by EDS. Conventionally sintered compacts of both the powders showed stability only when sintered at 700°C and beyond. The maximum shrinkage/densification occured around 450°C for both the powders and the densification rate observed in Fe-Cu is three times higher than Fe. This enhanced densification in Fe-Cu is attributed to an enhanced diffusivity of Fe atoms in the transient liquid Cu layer formed at the interfaces. The microstructure of Fe-Cu is completely free from any separate oxide phase unlike in samples of Fe sintered at 700°C that contain ultrafine oxide grains. This was explained on the basis of role played by acrawax, a lubricant, admixed to increase the green density. Based on the sintered densities of both SPS and conventional sintered compacts, residual oxide content of the compacts sintered at different temperature and experimentally observed shrinkage rate a phenomenological model has been proposed for the possible sequence of processes occurring during sintering of these nanopowders. The major findings of this work are summarized in chapter 6 and chapter 7 details the scope for the future work.

There exist large number of techniques for the preparation of nanostructured materials. Among them the preparation of nanopowders by gas/vapour condensation is a popular one. Because of very high level of surface to volume ratio, powders of metals which may or may not be reactive in the bulk form undergo vigorous oxidation. Oxidation once initiated continues in an auto catalytic fashion leading to a rise in temperature further increasing the oxidation rate. Therefore, the nanopowders are consolidated in situ under high vacuum. Alternatively a thin passivating oxide layer of few nm can be produced by slow exposure to air. Such powders lend themselves to be handled in further processing in ambient atmosphere. The main objective of the present research is to understand the various scientific and technological issues involved in preparing such passivated nanopowders by levitational gas condensation (LGC) technique, a relatively less explored vapour condensation process and their subsequent consolidation by the powder metallurgical route of compaction and sintering. The nanopowders systems studied are Fe and Fe-Cu (4 wt. %Cu). In chapter 1 a brief review of the gas condensation process and the consolidation behavior of nanopowders produced by this method were carried out. Existing knowledge on various topics relevant for the present study like formation of nanoparticles, agglomeration during gas condensation, physical, structural and chemical nature of the passive layer formed during passivation, compaction and sintering behaviour of this passivated nanopowders were discussed. Chapter 2 details the synthesis of Fe nanopowders by levitational gas condensation process and its physical and structural characteristics. The nanopowders in the as synthesized condition showed extremely low packing density due to loosely packed weakly interlocked agglomerates. The nanoparticles manifest as three dimensional reticulated spongy structure composed of chains of these nanoparticles. Heat transfer calculation carried out to determine the particle temperature at different distance from the levitating drop indicates that the nanoparticles can be ferromagnetic at a distance of less than 2 mm away from the levitation drop and hence the magnetic nature of the materials plays an important role in the formation of nanoparticle chains and spongy agglomerates. Passivation of the nanopowders by slow exposure to air produces 3-4 nm thick oxide layer (Fe3O4) over α-Fe and the volume of these oxides was around 45%. The 3rd chapter presents and discusses the results of Fe-Cu alloy nanopowder synthesized by levitating gas condensation process. While synthesis of elemental nanopowders by gas condensation is straight forward as the operating conditions only influence the particle size, alloys require careful control of the levitating drop composition. Although initially we start the process with levitated drop of required composition, the vapour generated will be richer in more volatile element (Cu in our case). Thus the composition of the levitated drop progressively becomes deficient in Cu which in turn reduces Cu in the vapour. Composition of the drop can be stabilised by continuous feeding of the alloy of required composition that can be estimated from the knowledge of equilibrium relation. To establish the equilibrium relationship between composition of the liquid and vapour in evaporation and condensation, phase diagram in the liquid and vapour region was calculated and was validated by determining composition of the drops. Good agreement between the drop composition and the composition predicted by the phase diagram were observed. Various physical, chemical and structural properties of the Fe-Cu nanopowders are characterized in detail using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and thermogravimetry (TG) analysis. The overall chemical composition of the Fe-Cu alloy nanopowders and of the individual agglomerates is same as the composition of feed materials used. However, Cu was found to segregate to the surface of the nanopowders which is attributed to minimization of surface energy with Cu at the surface. The total weight loss observed in TG in flowing hydrogen indicates that the surface passive layer of Fe-Cu appears to be very thin compared to Fe. The consolidation behaviour of both Fe and Fe-Cu nanopowders was studied by both conventional and spark plasma sintering (SPS) and are discussed in chapter 4. The as collected nanopowders from the apparatus have extremely low apparent density. The powders were further subjected to soft milling in a ball mill under ethanol to disentangle the agglomerates there by improving the pack density. A tenfold improvement was achieved thus making it suitable for consolidation. Uniaxial compaction of these powders for conventional sintering at pressure below 200 MPa yielded compacts free from defects. However, at higher pressure the compacts cracks and delaminates during ejection stage. Analysis of the compaction curves helped us to understand various processes involved during compaction as well as providing explanation for lower green density of Fe-Cu powder compared to Fe. Conventional sintering of the nanopowders compacts were carried out in the flowing hydrogen atmosphere in a laboratory vacuum furnace over wide range of temperatures. Instrumented sintering experiments were also carried out in a dilatometer under hydrogen atmosphere to evaluate shrinkage rate at different temperatures. SPS were carried out under 10 Pa vacuum at a compaction pressure of 250 MPa in WC-Co die cavity. The stability, density and residual oxygen content of the sintered compacts were quantified. Detailed microstuctural analysis of the sintered samples were also carried out using optical microscopy, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy and quantitative composition analysis by EDS. Conventionally sintered compacts of both the powders showed stability only when sintered at 700°C and beyond. The maximum shrinkage/densification occured around 450°C for both the powders and the densification rate observed in Fe-Cu is three times higher than Fe. This enhanced densification in Fe-Cu is attributed to an enhanced diffusivity of Fe atoms in the transient liquid Cu layer formed at the interfaces. The microstructure of Fe-Cu is completely free from any separate oxide phase unlike in samples of Fe sintered at 700°C that contain ultrafine oxide grains. This was explained on the basis of role played by acrawax, a lubricant, admixed to increase the green density. Based on the sintered densities of both SPS and conventional sintered compacts, residual oxide content of the compacts sintered at different temperature and experimentally observed shrinkage rate a phenomenological model has been proposed for the possible sequence of processes occurring during sintering of these nanopowders. The major findings of this work are summarized in chapter 6 and chapter 7 details the scope for the future work.

碩士
國立臺北科技大學
能源與冷凍空調工程系
106
In recent years, the global warming effect causes the electric power consumption of the air-conditioning in the tropical and subtropical area to increase dramatically. Therefore, how to reduce the power consumption of air-conditioning has became a very important issue. The split-type air conditioner (SAC) is widely used in a household and an office because of its compact size, smooth appearance, low noise, and easy to adjust the volume flow rate. In order to improve the performance of air conditioners, this study adopted the Computational Fluid Dynamics (CFD) software-ANSYS FLUENT to analyze the internal flow field and the heat transfer performance of the indoor unit of a SAC. This study developed a theoretical model for the two-dimensional numerical simulation of the indoor unit of a small-sized SAC. The compact fins of the evaporator were treated as a porous zone composed of the air and aluminum fins. To simulate the thermal performance of the evaporator, the non-equilibrium thermal model was used to predict the temperature distributions of the aluminum fins and the air respectively. The VOF (Volume of Fluid) model was adopted to simulate the behavior of the liquid water and wet air (composed of dry air and water vapor) during the condensation process occurring on the evaporator. To predict the condensation rate on the evaporator, the Fickian law, Lee Model equation and Mass Transfer equation was employed in this study. Incorporating the evaporator with the dynamic rotation of the cross-flow fan (CFF), numerical simulation predicted the velocity, temperature and water vapor fields, condensation rate, and the heat transfer performance of the evaporator of the indoor unit. Moreover, the volume flow rate of the SAC, the total heat transfer rate of the evaporator, and absolute humidity at the discharging outlet predicted by the numerical method were also compared with experimental results. The relative errors between both results were less than 9%, revealing that both results agreed well and the model developed in this study was accurate.

Composition of the newly formed secondary organic aerosol (SOA) generated by ozonolysis of the cyclohexene (model precursor) and α-pinene was studied using liquid chromatography coupled to electrospray ionization tandem mass spectrometry (LC-ESI/MSn). SOA was generated in the flow-tube reactor under standard conditions: 20°C and 1 atm. and the reaction time less than 1 min. In an attempt to resolve the current ambiguities, regarding the structure of the α-pinene SOA nucleating agents, analytical methods for analysis of α-acyloxyhydroperoxy aldehydes and high molecular weight (HMW) compounds containing carboxylic group were developed. Both groups of those compounds are currently considered as the potential nucleating agents. However, no analytical evidence proving the presence of α-acyloxyhydroperoxy aldehydes in the SOA samples have been presented. Also, very limited experimental data, indicating that the nucleating agents are acidic oligomers is currently available. The α-acyloxyhydroperoxy aldehydes were analyzed with LC-ESI/MSn for the first time. Analysis of the tandem mass spectra of the α-acyloxyhydroperoxy aldehydes ammonia adducts was used to propose the general fragmentation mechanism, supported by the analysis of the isotopically labeled analogs. The proposed mechanism was used to predict the mass spectrum of the α-acyloxyhydroperoxy aldehydes that could not be synthesized. After analyzing the SOA samples, generated in the flow-tube reactor, it was concluded that α-acyloxyhydroperoxy aldehydes were not formed in significant quantities, and are unlikely to participate in the aerosol nucleation. Direct analytical evidence was found, arguing against the gas-phase nucleation and proving that acidic oligomers are formed in the early stages of SOA formation. Also, based on the acquired experimental data, it was concluded that the reactive uptake of carbonyl compounds is an important growth mechanism for the freshly formed SOA. For the first time, isotopically labeled analog of cyclohexene (cyclohexene-d10) was used to propose the structures for the up-to-date unknown oligomers. The acquired experimental data point out the need for revision of the current α-pinene SOA nucleation mechanism.
Skład świeżo powstałego wtórnego aerozolu organicznego (secondary organic aerosol, SOA) został przeanalizowany za pomocą chromatografii cieczowej połączonej z tandemową spektrometrią mas z jonizacją przez elektrorozpylanie (LC-ESI/MSn). SOA został wytworzony w reaktorze przepływowym w standardowych warunkach temperatury i ciśnienia: 20°C i 1 atm. a czas reakcji wynosił < 1 min. Aby rozstrzygnąć obecne niepewności dotyczące struktury zalążków nukleacji SOA powstałego w wyniku ozonolizy α-pinenu, zostały opracowane metody analizy α-acyloksyhydroperoxy aldehydów oraz oligomerów zawierających grupę karboksylową. Obydwa typy związków są obecnie rozważane, jako potencjalne zalążki nukleacji. Jednak, do tej pory nie zostały przedstawione żadne bezpośrednie dowody potwierdzające obecność α-acyloksyhydroperoxy aldehydów w próbkach SOA. Ponadto, tylko niewielka ilość danych wskazuje, iż zalążkami nukleacji są kwasowe oligomery. α-Acyloksyhydroperoxy aldehydy po raz pierwszy zostały przeanalizowane za pomocą LC-ESI/MSn. W wyniku analizy widm fragmentacyjnych został zaproponowany ogólny mechanizm fragmentacji adduktów amonowych α-acyloksyhydroperoxy aldehydów; mechanizm ten został potwierdzony za pomocą analizy izotopowo znaczonych analogów. Zaproponowany mechanizm fragmentacji został wykorzystany żeby przewidzieć widmo masowe α-acyloksyhydroperoxy aldehydów, które nie mogły być zsyntezowane. W próbkach SOA wytworzonych w reaktorze przepływowym, α-acyloxyhydroperoxy aldehydy nie zostały wykryte w znaczących ilościach i prawdopodobnie nie brały udziału w procesie nukleacji aerozolu. Otrzymane wyniki wskazują, iż nukleacja prawdopodobnie nie zachodzi w fazie gazowej. Jednocześnie, zostało udowodnione, że kwasowe oligomery są wytwarzane już na wczesnych etapach formowania SOA. Stwierdzono także, iż absorpcja związków karbonylowych w wyniku formowania się oligomerów jest ważnym mechanizmem wzrostu cząstek aerozolu na czesnych etapach jego powstawania. Po raz pierwszy, izotopowo znaczony prekursor (cykloheksen-d10) został wykorzystany do zaproponowania struktur do tej pory nieznanych oligomerów. Zidentyfikowane oligomery najprawdopodobniej powstały w wyniku reakcji związków karbonylowych. Wyniki przedstawione w tej pracy wskazują, iż obecnie zaproponowany mechanizm nukleacji powinien zostać zaktualizowany.

1 Abstract: Cryopreservation of cells is a complex process with many useful applications in basic biological research, medicine and agriculture. In this work we deepened the current understanding of the cryopreservation process both at physical and biological level. Results include characteristics of selected cryoprotectants (primarily DMSO, trehalose, antifreeze protein ApAFP752) in liquid phase, during phase transition and in solid phase, as well as their impact on cryopreserved cells states. Specifically, the level of cell viability, state of cell membrane and condition of cell nucleus (nuclear membrane, chromatin condensation, DNA strand breaks) are monitored over several time points after thawing. It is shown that S-phase cells (NHDF and MCF7 lines) suffer massive collapse of replication forks during cryopreservation which makes them much less suitable for cryopreservation than cells in other phases of the cell cycle. Several methods (most importantly Atomic Force Microscopy, Confocal Fluorescence Microscopy and Flow Cytometry) were used to examine the post-thaw state of cryopreserved cells. The acquired insights into cryodamage of cells can lead to optimization of current cryopreservation protocols and to more thorough evaluation of efficacy of future novel cryoprotectants.

Space is known as a very aggressive and hostile environment and its degradative effects on spacecraft materials can compromise the success of the entire mission. A few types of space weather impacts on spacecrafts have been detected and the main ones are for example: space-plasma that causes surface charging on the structures with consequently biasing of instrument and physical damages; microparticles and space debris which can cause abrasions on surfaces and structural damages; UV radiation, galactic cosmic rays and solar particle events that lead to a thermal, electrical, optical and structural integrity degradation of materials and many damages in the electronic components; large gradients of temperature when, for example, space vehicles are illuminated or not by sunlight lead to a degradation of polymeric materials as well as the presence of atomic oxygen, especially in LEO orbit, that corrodes the exposed polymeric material surfaces. It is therefore necessary to provide and find solution to protect and properly isolate the spacecraft components from the external space environment. Multifunctional coatings could play a key-role in protecting and safeguarding the various spacecraft components, of different nature, from the surrounding environment. For example, it’s well known that the non-linear nature of the MLI details, such as its shape, finishing details, grounding hardware and perforation patterns, as well as the nonlinear response of metallic contact points, contribute to passive intermodulation products. For these reasons, ESA has recently funded research projects (Artes 5.1 and 5.2) to find a solution for this problem. One of the most promising concepts is the use of frequency selective surfaces as layers of the MLI. This is accomplished by using nanostructured carbon-based films on membranes, which can also improve the protection of the payload by the MLI (and in general by flexible membranes) with respect to space radiations and impact events. Multifunctional films containing carbon nanoparticles are currently investigated also to create sensors for monitoring the radiation absorbed by astronauts during extra vehicular activities (EVA) or as new and advanced grounding systems to mitigate plasma-induced spacecrafts charging. Further novel space-based applications of carbon-based multifunctional films are future membrane reflector spacecraft. These ones are a promising key technology to deliver cost-effective space-based applications such as communication antennae, optical telescopes and solar energy collectors. The main objectives of my Ph.D. research are to design and realize carbon-based nanocomposite coatings with tailored multifunctional properties for spacecraft components. The research was focused on the development and design of nanocomposite films containing carbon nanoparticles, namely carbon nanotubes and graphene nanoplatelets, which have unique multifunctional properties. The selected carbon nanoparticles were added to different types of aerospace-grade polymer matrices at several concentrations. Nanocomposite films will be fabricated on different types of substrates like Mylar sheets, carbon-fibers reinforced polymer (CFRP) composite laminates or metal substrates that are widely used in spacecraft sub-systems. Such multifunctional coatings were fabricated on one side with the aim to protect and safeguard the various spacecraft components, of different nature, from the surrounding hostile space environment, especially from ultraviolet radiations in C band (UV-C) and electrically charged particles coming from space-plasma, and on the other side to achieve thermal performance of the unit increased over time, by increasing the heat transfer coefficients, resulting in an ideal design of heat exchangers widely used in the aerospace field to control, for example, the temperature of on-board electronic components. The development of polymeric nanocomposites films with tailored excellent and multifunctional mechanical, electrical, thermal and hydrophobic properties depends on the properties and geometrical features of the nanofillers, CNTs or graphene, their grade of dispersion within the polymeric matrix as nano-reinforcements, their interaction with the polymeric matrix and the alignment of the nanofillers in the matrix as well as the fabrication process of films. For these reasons, the definition of the carbon nanoparticles, their concentration and dispersion process in the polymer matrices, the investigation and optimization of different deposition techniques such as spin-coating, spray-coating, drop-casting and bar-coating, were important preliminary steps of my PhD research, in order to optimize the wanted multifunctional properties of the film. This Ph.D. research can be summarized in 5 research activities. The first one concerns the analysis and the investigation of the effects of space-abundant UV-C radiation on the surface (hydrophobic and electrical) properties of carbon-based nanocomposite films deposited on flexible Mylar substrates by spin-coating process. The second one is about the study of the spray-coating deposition process and the investigation of the role of its working parameters in setting the morphology and the electrical performance of MWCNT-based nanocomposite films. The spray-coating technique, as opposed to the previous used spin-coating one, allows to fabricate larger polymeric coatings in terms of covered area on planar and not substrates, becoming an attractive method for large scale production of coatings. In particular, the fabrication of uniformly electrically-conductive coatings on Mylar substrate can allow the mitigation of electromagnetic interferences and plasma-induced spacecraft charging, and so this aspect it was assessed. The third study is the design of nanocomposite coatings by bar-coating process on carbon/fibers reinforced polymer (CFRP) composite structures for electrostatic charge (ESC) build-up mitigation for spacecraft and with the aim to realize new and innovative advanced grounding systems for charging mitigation as well. The fourth research activity concerns the application of the electrical resistance tomography (ERT) technique to the detection of surface conductivity changes induced by UV exposure. This technique in combination with the fabricated UV-sensitive coatings containing DNA-functionalized graphene can provide a health monitoring method for composite materials and structures that are exposed to damaging levels of UV radiation. At last, the main idea of the fifth study is to fabricate hydrophobic and, in the same time, thermal conductive efficient nanocomposite coatings applied on aluminum substrate that can reduce the filmwise condensation encouraging the dropwise one leading to increased thermal performances resulting in an ideal design of heat exchangers, used for example in the aerospace sector to control the temperature of on-board electronic components.