In this thesis, ammonia (NH3) decomposition was assessed as a fuel processing technology for producing on-demand hydrogen (H2) for portable and distributed fuel cell applications. This study was motivated by the present lack of infrastructure to generate H2 for proton exchange membrane (PEM) fuel cells. An overview of past and recent worldwide research activities in the development of reactor technologies for portable and distributed hydrogen generation via NH3 decomposition was presented in Chapter 2. The objective was to uncover the principal challenges relating to the state-of-the-art in reactor technology and obtain a basis for future improvements. Several important aspects such as reactor design, operability, power generation capacity and efficiency (conversion and energy) were appraised for innovative reactor technologies vis-à-vis microreactors, monolithic reactors, membrane reactors, and electrochemical reactors (electrolyzers). It was observed that substantial research effort is required to progress the innovative reactors to commercialization on a wide basis. The use of integrated experimental-mathematical modelling approach (useful in attaining accurately optimized designs) was notably non-existent for all reactors throughout the surveyed openliterature. Microchannel reactors were however identified as a transformative reactor technology for producing on-demand H2 for PEM cell applications. Against this background, miniaturized H2 production in a stand-alone ammonia-fuelled microchannel reactor (reformer) washcoated with a commercial Ni-Pt/Al2O3 catalyst (ActiSorb® O6) was demonstrated successfully in Chapter 3. The reformer performance was evaluated by investigating the effect of reaction temperature (450–700 °C) and gas-hourly-space-velocity (6 520–32 600 Nml gcat -1 h-1) on key performance parameters including NH3 conversion, residual NH3 concentration, H2 production rate, and pressure drop. Particular attention was devoted to defining operating conditions that minimised residual NH3 in reformate gas, while producing H2 at a satisfactory rate. The reformer operated in a daily start-up and shut-down (DSS)-like mode for a total 750 h comprising of 125 cycles, all to mimic frequent intermittent operation envisaged for fuel cell systems. The reformer exhibited remarkable operation demonstrating 98.7% NH3 conversion at 32 600 Nml gcat -1 h-1 and 700 °C to generate an estimated fuel cell power output of 5.7 We and power density of 16 kWe L-1 (based on effective reactor volume). At the same time, reformer operation yielded low pressure drop (<10 Pa mm-1) for all conditions considered. Overall, the microchannel reformer performed sufficiently exceptional to warrant serious consideration in supplying H2 to low-power fuel cell systems. In Chapter 4, hydrogen production from the Ni-Pt-washcoated ammonia-fuelled microchannel reactor was mathematically simulated in a three-dimensional (3D) CFD model implemented via Comsol Multiphysics™. The objective was to obtain an understanding of reaction-coupled transport phenomena as well as a fundamental explanation of the observed microchannel reactor performance. The transport processes and reactor performance were elucidated in terms of velocity, temperature, and species concentration distributions, as well as local reaction rate and NH3 conversion profiles. The baseline case was first investigated to comprehend the behavior of the microchannel reactor, then microstructural design and operating parameters were methodically altered around the baseline conditions to explore the optimum values (case-study optimization). The modelling results revealed that an optimum NH3 space velocity (GHSV) of 65.2 Nl gcat -1 h-1 yields 99.1% NH3 conversion and a power density of 32 kWe L-1 at the highest operating temperature of 973 K. It was also shown that a 40-μm-thick porous washcoat was most desirable at these conditions. Finally, a low channel hydraulic diameter (225 μm) was observed to contribute to high NH3 conversion. Most importantly, mass transport limitations in the porouswashcoat and gas-phase were found to be negligible as depicted by the Damköhler and Fourier numbers, respectively. The experimental microchannel reactor produced 98.2% NH3 conversion and a power density of 30.8 kWe L-1 when tested at the optimum operating conditions established by the model. Good agreement with experimental data was observed, so the integrated experimental-modeling approach used here may well provide an incisive step toward the efficient design of ammonia-fuelled microchannel reformers. In Chapter 5, the prospect of producing H2 via ammonia (NH3) decomposition was evaluated in an experimental stand-alone microchannel reactor wash-coated with a commercial Cs-promoted Ru/Al2O3 catalyst (ACTA Hypermec 10010). The reactor performance was investigated under atmospheric pressure as a function of reaction temperature (723–873 K) and gas-hourly-space-velocity (65.2–326.1 Nl gcat -1 h-1). Ammonia conversion of 99.8% was demonstrated at 326.1 Nl gcat -1 h-1 and 873 K. The H2 produced at this operating condition was sufficient to yield an estimated fuel cell power output of 60 We and power density of 164 kWe L-1. Overall, the Ru-based microchannel reactor outperformed other NH3 microstructured reformers reported in literature including the Ni-based system used in Chapter 3. Furthermore, the microchannel reactor showed a superior performance against a fixed-bed tubular microreactor with the same Ru-based catalyst. Overall, the high H2 throughput exhibited may promote widespread use of the Ru-based micro-reaction system in high-power applications. Four peer-reviewed journal publications and six conference publications resulted from this work. / PhD (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

Ce travail s’inscrit dans le cadre de l’étude d’un système de stockage et de restitution des surplus d’énergie électrique de sources renouvelables. L’objectif de l’étude est d’évaluer la capacité du concept à absorber l’intermittence de la production électrique à travers l’analyse de la flexibilité des procédés choisis. En phase de stockage, l’unité utilise un procédé d’électrolyse basse température à membrane échangeuse de proton (PEM) pour produire l’équivalent de 200 MW d’hydrogène. Ce gaz sera combiné au dioxyde de carbone dans une série de réacteurs de méthanation pour former l’équivalent de 155 MW de substitut de gaz naturel. La phase de déstockage est réalisée au sein d’un cycle d’oxy-combustion d’une puissance installée de 480 MW. Ce cycle permet de restituer l’énergie contenue dans les gaz stockés et de produire le CO2 requis pour le procédé de méthanation. L’étude énergétique en régime stationnaire de cette installation montre que l’efficacité du procédé d’électrolyse atteint 69,3%, celle du procédé de méthanation 82,2% et celle du cycle d’oxy-combustion 51,8% sur PCS. L’analyse en régime transitoire de la phase Power-to-Gas permet d’identifier les stratégies de contrôle adaptées aux variations temporelles de conditions opératoires. Ces stratégies visent à permettre au système de couvrir des plages de fonctionnement plus larges et d’absorber plus de puissance électrique. Il s’est avéré que la production du méthane de synthèse peut s’étendre sur des plages de fonctionnement allant de 48% à 100% de la puissance nominale sans aucun apport énergétique extérieur. Le cas d’étude réalisé pour le couplage de l’unité avec un parc éolien de 300 MW permet d’évaluer les performances du Power-to-Gas en fonction de la variation de la source électrique. / The present work deals with the conceptual study and process design of a storage and recovery unit for renewable energy. The suggested concept is able to absorb the intermittency of the electrical production as a result of the flexibility of the chosen processes. During the storage phase, the unit uses a Proton Exchange Membrane electrolysis system to produce 200 MW of hydrogen, which will then be combined to carbon dioxide in a series of methanation reactors to generate up to 155 MW of Substitute Natural Gas. The recovery phase is carried out in a 480 MW oxy-combustion cycle which is not only able to restore the electrical energy but also provides the required carbon dioxide for the methanation process. The conducted steady state evaluation as well as the sensitivity analysis for the studied plant showed that the overall efficiency on HHV basis can reach up to 69.3% for the electrolysis process, 82.2% for the methanation process and 51.8% for the oxy-combustion cycle. The follow-up unsteady state analysis of the Power-to-Gas process aimed to identify the necessary control strategies adapted to operating conditions variation over time. Such strategies should enable the system to cover a wider load range and subsequently absorb more electrical power. It was found that, by making the right adjustments, the production of synthetic methane can be fulfilled at ranges between 48% and 100% of the nominal power without any external energy requirement. A case study was carried out where the unit was coupled with a 300 MW wind to assess the performance of the Power-to-Gas process under fluctuating electrical source conditions.

Étant une des nouvelles sources délivrant des énergies électrique et thermique décentralisées, les piles à combustible offrent une meilleure efficacité énergétique et des émissions réduites pour un développement durable. Ce mémoire est axé particulièrement sur l’étude des piles à combustible à membrane échangeuse de protons (PEM), et sur les phénomènes physico-chimiques dont elles sont le siège. Un modèle 2D dynamique a été développé et résolu numériquement par la méthode des éléments finis au moyen du logiciel COMSOL Multiphysics. Les caractéristiques statiques et dynamiques simulées sont confrontées aux mesures effectuées sur un banc de test équipé d’une monocellule de type PEM de 100cm2 du laboratoire GREEN. Des études paramétriques, telles que l’influence des conditions opératoires, différentes sollicitations en courant, ont été simulées et expérimentées. Le comportement dynamique de la monocellule à un échelon de courant, et plus particulièrement à un couplage direct sur une capacité, a souligné l’importance du phénomène de la double couche électrique aux interfaces membrane/électrode dans la description précise des transitoires rapides. Enfin, la spectroscopie d’impédance, très répandue comme outil de caractérisation de la pile, a été mise en œuvre en simulation, permettant ainsi l’analyse des effets de cette méthode de mesure sur les grandeurs locales du cœur de pile / Being a new source of supplying electrical and thermal decentralized energy, the fuel cells offer better energy efficiency and reduced emissions for sustainable development. This thesis deals with the physicochemical phenomena that occur in a single cell of fuel cell proton exchange membrane. A 2Ddynamic model was developed and solved numerically by the finite element method using thesoftware COMSOL Multiphysics. The simulated static and dynamic polarization curves are confronted with measurements made on a 100cm² single cell test bench that belongs to GREEN Laboratory. Aparametric study, such as the influence of operating conditions, different stress current has been simulated and tested. The single cell dynamic behavior to a current step and more particularly to adirect connection to capacitor has underlined the importance of the electrical double layer phenomenon, located at the membrane / electrode interfaces, to describe precisely fast transients.Finally, spectroscopy impedance as a tool widely used to characterize the cell has been implemented in simulation allowing the analysis of the effects of this measurement method on the local parameters

Fuel cells are electricity generators which convert chemical energy of hydrogen directly to electricity by means of electrochemical oxidation and reduction reactions. A single proton exchange membrane (PEM) fuel cell can only generate electricity with a potential between 0.5V and 1V. The useful potential can be achieved by stacking cells in series to form a PEM fuel cell stack. There is a potential to utilize 100W class fuel cells. Fuelling is the major problem of the portable fuel cells. The aim of this thesis is to design and manufacture a PEM fuel cell stack which can be used for portable applications. The PEM fuel cell stack is planned to be incorporated to a NaBH4 hydrolysis reactor for H2 supply. Within the scope of this thesis a new coating technique called &ldquo / ultrasonic spray coating technique&rdquo / is developed for membrane electrode assembly (MEA) manufacturing. New metal and graphite bipolar plates are designed and manufactured by CNC technique. A fuel cell controller hardware is developed for fuel supply and system control. The power densities reached with the new method are 0.53, 0.74, 0.77, and 0.88 W/cm2 for 20%, 40%, 50%, 70% Pt/C catalyst by keeping 0.4mg Pt/cm2 platinum loading constant, respectively. The power density increase is 267% compared to &ldquo / spraying of catalyst ink with air pressure atomizing spray gun&rdquo / . All parts of the PEM fuel cell stack designed were produced, assembled, and tested. The current density reached is 12.9A at 12 V stack potential and the corresponding electrical power of the stack is 155W.

1. Membranes échangeuses de protons à haute température (HT-PEM) pour application dans les piles à combustible:Le succès des piles à combustible à base de HT-PEM dépend fortement du matériau membranaire. D’importants progrès ont été accomplis dans la conception de PEMs à transport facilité de protons. L'objectif de la première partie de ce travail de thèse était de fabriquer des membranes électrolytes à haute conductivité, capables de fonctionner au-dessus de 120°C dans des conditions anhydres, sans acides minéraux, et sans sacrifier la résistance mécanique. La stratégie suivie combine l’utilisation de micro-filtres (support) à base de polybenzimidazole (PBI) présentant un réseau de pores ordonnés, et de liquides ioniques (ILs)à base de polyimidazolium comme phase conductrice. Deux types de micro-filtres de PBI ont été préparés: avec un réseau de pores droits (SPBI), ou avec une structure poreuse hiérarchique (HPBI). Les ILs polymérisés (PIL) suscitent un grand intérêt comme tous les électrolytes flexibles à l'état solide en raison de leur sécurité d’utilisation et de leur bonne stabilité thermique, chimique et électrochimique. Dans ce travail, un IL monomèrique protique 1-H-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide a été choisi pour sa conductivité protonique élevée, sa faible rétention d'eau et sa bonne stabilité thermique. Puisque les performances d’une PEM formée par immersion d’un support poreux dans un IL dépendent surtout de la structure poreuse du support, il est essentiel d’optimiser l’architecture des pores réservoirs. Ainsi, nos travaux visent à améliorer à la fois la conductivité ionique et la stabilité dimensionnelle des PEMs à base de PIL par une conception appropriée de l'architecture poreuse. En effet, la faible stabilité dimensionnelle et mécanique du poly[1-(3H-imidazolium)éthylène] bis(trifluorométhanesulfonyl) imide est améliorée grâce à son infiltration dans un support PBI architecturé. La configuration d'infiltration, l'addition d’agent réticulant et les conditions de polymérisation UV "in situ" ont été considérées comme paramètres d'optimisation pour les deux types de micro-tamis en PBI.2. Membranes à base de liquide ionique supporté (SILM) pour la valorisation du méthane:La valorisation du gaz naturel, intégrant l'élimination de CO2 et N2, est l’une des applications de séparation des gaz industriels où les membranes sont une alternative prometteuse à petite échelle. L'objectif de nos travaux était de développer des membranes de type SILM, sélectives au CH4. Notre stratégie combine des micro-tamis à base polybenzimidazole (PBI) comme supports présentant une bonne endurance et de bonnes propriétés thermiques, et des liquides ioniques (ILs) protiques avec des ions imidazolium et trifluorométhane sulfonylimide pour la solubilité du CH4. Bien que la faible pression de vapeur du IL protique atténue sa volatilité dans les SILMs traditionnels, son expulsion hors des pores reste une préoccupation majeure. Un design approprié du support, avec des pores submicroniques, combiné à un IL de tension superficielle élevée, devrait générer des SILMs plus stables, adaptées aux applications à pression transmembranaire modérée ou élevée. Ainsi, des supports PBI à porosité aléatoire (RPBI), obtenus par séparation de phase, ont été largement utilisés. En outre, la polymérisation des RTILs peut fournir d’autres avantages en termes de sécurité, de stabilité et de propriétés mécaniques. Dans cette étude, trois classes de SILMs à base de PBI, avec le IL protique 1-H-3-methylimidazolium bis(trifluoromethane sulfonyl)imide (IL), le monomérique 1-H-3-vinyllimidazolium bis(trifluoromethane sulfonyl)imide (MIL) et le polymérique poly[1-(3H-imidazolium)ethylene] bis(trifluoromethanesulfonyl)imide (PIL) ont été fabriqués avec succès et caractérisées en perméation de gaz purs. Des membranes hautement permsélectives au méthane ont été obtenues, qui sont très prometteuses pour la séparation de mélanges de gaz tels que CH4/N2 / 1. High temperature Proton Exchange Membranes (HT-PEMs) for Fuel Cell applications:The success of the High temperature proton exchange membrane fuel cell (HT-PEMFC) direction is very much dependent on the development of the membrane material. With facilitated proton transport chemistries, great progresses in designing and fabricating facilitated PEMs have been accomplished. The objective of this first part of the PhD work was to fabricate highly conductive electrolyte membranes capable to operate above 120°C under anhydrous conditions and in the absence of mineral acids, without sacrificing the mechanical behavior. The followed rationale is based on the combination of polybenzimidazole (PBI) microsieves as structural supports and poly-imidazolium based ionic liquid (IL) moieties as conducting phase. Two types of PBI microsieves have been prepared following two different microfabrication processes: straight porous PBI and hierarchically structured PBI microsieves.Polymeric ionic liquids (PILs) have triggered great interest as all solid-state flexible electrolytes because of safety and superior thermal, chemical and electrochemical stability. In this part, the 1-H-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide has been mainly selected due to its high proton conductivity, low water uptake values as well as thermal stability.The consecution of a polymeric container with optimized pore architecture is extremely essential since the performance of PEM based on immersing a porous support into ILs, mainly depends on the porous structure. Thus, our research efforts have been directed to improve both, the ion conductivity and the dimensional stability of the PIL supported PEMs by a proper design of the porous architecture. Herein, the diminished dimensional and mechanical stability of poly[1-(3H-imidazolium)ethylene]bis(trifluoromethanesulfonyl)imide has been improved thanks to its infiltration on a PBI support with specific pore architecture. The infiltration configuration, cross-linker addition and “in situ” UV polymerization conditions were taken as optimization parameters for both PBI type microsieves.2. Supported Ionic liquid membranes (SILMs) for methane upgrading:The natural gas upgrading, i.e. removal of CO2 and N2, is one of the major industrial gas separation application where membranes arise as promising alternative at small scale.The objective of this second part of the work was to develop CH4 selective Supported Ionic Liquid Membranes (SILMs). Once again, the rationale followed is based on the combination of PBI microsieves as structural supports, to take advantage of its endurance and thermal properties, and protic ILs with imidazolium and trifluoromethane sulfonyl)imide ions due to their CH4 solubility properties. Although the negligible protic IL vapor pressure alleviates one of the problems associated with traditional SILMs, namely liquid volatility; expulsion of the liquid from the membrane pores is a major concern. A proper design of the support, with sub-micron pores, combined with IL having high surface tension could lead to SILM with adequate physical stability for applications involving moderate to high trans-membrane pressures. Therefore, random porous PBI supports, obtained by phase separation method, have been extensively used. In addition, polymerization of RTILs could provide additional advantages in terms of safety, stability and mechanical properties.In this study, three classes of SILMs, based on PBI with the 1-H-3-methylimidazolium bis(trifluoromethane sulfonyl)imide, the 1-H-3-vinylimidazolium bis(trifluoromethane sulfonyl)imide and the poly[1-(3H-imidazolium)ethylene] bis(trifluoromethanesulfonyl)imide have been successfully fabricated and characterized by single gas permeation measurements. Results revealed that the prepared membranes were highly selective to CH4 and thus very promising for CH4/N2 gas mixture separation.

Les piles à combustible à membrane échangeuse de protons (PEMFC) constituent une alternative aux moteurs thermiques utilisés dans le cadre d’applications transport ou dans le cadre d’applications stationnaires. Cependant, une large commercialisation des PEMFC dépend des progrès qui peuvent être réalisés pour améliorer leur fiabilité et leur durabilité. La PEMFC est sujette à plusieurs types de dégradations complexes et non entièrement maitrisées qui varient en fonction des conditions de fonctionnement. Cependant, il est admis qu’il est souhaitable de faire fonctionner la PEMFC à distributions de courant uniformes car des distributions de courant hétérogènes entraînent une mauvaise utilisation des réactifs et des catalyseurs, une diminution des performances globales et une possible dégradation des matériaux constitutifs du coeur de la pile. De nouvelles stratégies de diagnostic doivent donc être proposées en s’appuyant sur les distributions de courant. Mes travaux de recherche consistent à développer un nouvel outil de diagnostic s’appuyant sur une mesure du champ électromagnétique externe (non invasive) rayonné par la pile PEMFC. Le champ magnétique possède l’intérêt d’être corrélé à la distribution locale du courant circulant à l’intérieur de la pile, et permet d’avoir des informations sur les performances locales. Cette distribution est liée aux conditions opératoires de la pile. Il est alors possible, à partir d’une signature magnétique de remonter à une information locale et à la cause des distributions de courant non uniformes. Des bases (vecteurs) qui contiennent les données des champs magnétiques issues des 30 capteurs disposés autour de la PAC sont construites à partir de distributions de courant spécifiques. Ces bases constituent un espace de représentation du comportement anormal de la PEMFC et permettront de d’élaborer des signatures caractérisant les fonctionnements indésirables. Ainsi, deux méthodes ont été développées pour permettre : (i) d’extraire des paramètres pertinents sur la répartition de la densité de courant traduisant les performances locales de la PAC, (ii) de classifier les différents modes de fonctionnements indésirables. La première méthode consiste à générer des résidus vectoriels en comparant le comportement réel du système (caractérisé par un vecteur mesure) avec les bases générées. Des variables qualitatives ont été élaborées pour classifier les modes de fonctionnement indésirables de la pile. La deuxième méthode consiste à extraire des paramètres à partir de la projection du vecteur mesure dans la direction des bases. La classification est réalisée dans des espaces 2D. Une validation des deux méthodes proposées a été effectuée à partir de mesures expérimentales sur une PEMFC de taille industrielle (stack GENEPAC de 40 cellules construit par le CEA et PSA). La pertinence des paramètres extraits a été vérifiée en s’appuyant sur des distributions de courant mesurées directement. Les modes de fonctionnement indésirables prédéfinis permettent de localiser les paramètres opératoires ayant conduit à l’évolution de la distribution de courant. Les outils ainsi réalisés sont très facilement transposables à d’autres piles PEMFC. / Proton exchange membrane fuel cell (PEMFC) is a potential alternative energy conversion device for stationary and automotive applications. Wide commercialization of PEMFC depends on progress that can be achieved to enhance its reliability and durability. The PEM fuel cell is subject to several types of complex and not fully mastered degradations which vary with operating conditions. It is desirable to operate the PEMFC at uniform current distribution because non uniform current distribution over the MEA could result in poor reactant and catalyst utilization, overall cell performance degradation as well as corrosion processes inside the PEM fuel cell. Therefore, new diagnostic strategies must be proposed, including choice of information gathered on the system and the fuel cell operation representation. My research is to develop a new diagnostic tool based on a measure of the external electromagnetic field (non-invasive) radiated by the fuel cell. The magnetic field has the advantage of being correlated to the local distribution of the current flowing inside the fuel cell (a physical indicator to obtain information on local performance of a fuel cell); it is linked to the local operating conditions: relative humidity level, temperature etc. It is then possible, from a magnetic signature to trace local information. Baselines (vectors) which contain the magnetic fields data generated by specific current distribution are built to characterize the magnetic field generated by the undesirable operation of the fuel cell. Baselines constitute a representation space of abnormal system behavior. Two methods have been developed to enable: (i) to extract the relevant parameters on the distribution of the current density resulting from PEM fuel cell stack local performance, (ii) to classify different types of undesirables operations. The first method is to generate vector residuals by comparing the actual behavior of the system (characterized by a measurement vector) with the baselines generated. Qualitative variables were created to classify the undesirable modes of PEM fuel cell stack operation. The second method is to extract parameters from the projection of the vector in the direction of measurement baselines. The classification is performed in 2D space. Validation from experimental measurements of the two proposed methods has been carried out on a commercial scale PEMFC (GENEPAC stack of 40 cells built by the CEA and PSA). The relevance of the extracted parameters was verified based on current density distributions measured directly. The undesirable predefined operating modes were used to locate the operating conditions parameters that led to the evolution of the current density distribution. The tools are made easily transferable to other PEMFC stack.

Made available in DSpace on 2014-06-11T19:27:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-02-29Bitstream added on 2014-06-13T19:35:06Z : No. of bitstreams: 1 mesquitaneto_c_me_ilha.pdf: 1673109 bytes, checksum: 0f8131abf5fc45715c92abece81e6a7a (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho é apresentado uma proposta de absorvedor de vibrações ajustável tipo viga sanduíche utilizando fluido Magnetoreológico no centro. Para o desenvolvimento deste projeto foi realizada uma revisão sobre os vários tipos de absorvedores e algumas aplicações. Em seguida foi realizado um estudo sobre o comportamento do fluido magnetoreológico, mostrando como este material inteligente varia suas propriedades quando submetido a um campo magnético. O objetivo do estudo foi verificar as propriedades do sistema para realização de um futuro controle, que é realizado através da variação do campo magnético. Avaliou-se, também, a relação com a corrente elétrica, quais os parâmetros que o influenciam e como podemos produzir um campo magnético com a intensidade desejada. Para avaliar as características do sistema foi utilizado o modelo no programa Ansys, com o objetivo de se verificar o comportamento do sistema. Para encontrar as características reais do sistema foi utilizado o modelo na forma de espaço de estados modais, identificado através do método PEM, Método de Predição de Erros (do inglês Prediction Error Methods PEM). Os testes experimentais foram realizados para se adquirir conhecimento do comportamento dinâmico deste tipo de fluido e, verificar se há repetibilidade nas medidas / This work presents a proposal of a tunable vibrations absorber type sandwich beam, using the Magnetorheologic fluid in the intermediate layer. For the development of this study a revision of some types of absorber with some applications was carried out. After that, a study of the behavior of the magnetorheologic fluid was carried through, showing as this intelligent material tunable its properties when submitted to a magnetic field. The objective of this analysis was to verify the properties of the system for implementation of a future control, which is based on the variation of the magnetic field. It was realized an analysis of the relation of the electric current and the parameters that influence it, in order to produce a magnetic field with the desired intensity. The characteristics of the system were verified through a mathematical model obtained with the software Ansys. The real characteristics of the system were found through the identification method PEM, Prediction Error Methods, using modal space states formulation. Experimental tests were carried out in order to obtain know how of the dynamic behavior of this type of material

Inledning: Myalgisk encefalomyelit/kroniskt trötthetssyndrom (ME/CFS) kännetecknas som en inflammation i hjärna och ryggmärg och karakteriseras framför allt av ihållande utmattning. Sjukdomen är ingen kultursjukdom eller lokal företeelse utan den förekommer i diverse åldrar, länder och sociala grupper. Ansträngningsutlöst försämring (PEM) är ett kardinalsymtom för sjukdomen. PEM kännetecknas av en förvärring av symtom efter rörelse, ortostatisk eller neuromuskulär stress och/eller kognitiv aktivitet. Syfte: Syftet var att beskriva upplevelsen och erfarenheten av ansträngningsutlöst försämring (PEM) hos personer med ME/CFS. Metod: En kvalitativ empirisk studie baserad på bloggar med deduktiv ansats. Livsvärldsteorin användes som en teoretisk referensram. Resultat: Resultatet visade att personer med ME/CFS beskrev PEM som en påfrestande och dramatisk upplevelse och att det krävdes ständiga anpassningar för att undvika försämringen. Situationen förvärrades ytterligare av ett bristfälligt och empatilöst bemötande inom sjukvården. Slutsats: På grund av känslighet för stimuli behöver varje handling gentemot personer med diagnosen ME/CFS reflekteras över huruvida den är till nytta eller till skada. För att förhindra PEM måste vården anpassas utifrån individuella ansträngningströsklar hos varje enskild person. Vidare forskning behövs om vilka förändringar som krävs för att säkerställa högkvalitativ omvårdnad. / Introduction: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is characterized as inflammation of the brain and spinal cord and is characterized above all by persistent fatigue. The disease ME/CFS is not a cultural disease or a local phenomenon and It occurs in various ages, countries and social groups. PEM is characterized by an exacerbation of symptoms after movement, orthostatic or neuromuscular stress and / or cognitive activity. Purpose: The aim of this study was to describe the experiences and the perceptions of post-exertional malaise (PEM) in people with ME/CFS. Method: The study was a qualitative empirical study with a deductive approach based on blogs. Lifeworld was used as a theoretical framework. Result: The results showed that people with ME / CFS described PEM as a stressful and dramatic experience and that constant adjustments were required to avoid this deterioration. The situation was further aggravated by a deficient and unempathetic response in healthcare. Conclusion: Due to abnormal sensitivity to stimuli, each intervention for persons diagnosed with ME / CFS needs to be reflected on whether it is beneficial or harmful. To prevent PEM, healthcare must be adjusted based on the individual effort thresholds of each person. Further research is needed on what improvements are required to ensure high-quality nursing.

To support the large­scale integration of renewables in electricity grids, power­to­X­to­power (P2X2P) systems have been proposed. These systems serve to increase the flexibility of thermal power plants while potentially providing both economic and environmental benefits by allowing power from the plant to be redirected into an electrolyzer and converted to a gaseous energy carrier. In this study, the feasibility of a P2X2P system consisting of a combined cycle gas turbine (CCGT) power plant coupled with a PEM electrolyzer in the Italian power sector has been investigated. A dynamic technoeconomic model has been developed for both hydrogen and ammonia­based systems together with a profit maximizing dispatch strategy for operation in both day­-ahead and balancing electricity markets. As a part of this, a PEM electrolyzer model was also developed and validated against experimental data. Notable technical improvements were observed as a consequence of the implementation of a P2X2P system in the form of avoided shutdowns and a more even power output. However, any economic and environmental benefits of such improvements were not observed as the addition of the P2X2P system led to a reduction in net present value as well as higher specific emissions of carbon dioxide. When the gaseous energy carrier was utilized as fuel in the CCGT, similar technical performances were achieved by the hydrogen­based and ammonia­based systems. Due to the increased investment cost demanded by the ammonia production process the hydrogen­based system thus seems most suitable for this setup. / För att möjliggöra en storskalig utbyggnad av förnyelsebar energi har power­to­X­to­power­system (P2X2P) föreslagits som en potentiell lösning. Genom att omdirigera electricitet från kraftverket till en elektrolysator och därmed omvandla denna till vätgas kan dessa system förbättra den tekniska flexibiliten hos värmekraftverk samtidigt som de har potential att medföra både ekonomiska och miljömässiga fördelar. Detta examensarbete har undersökt den tekno­ekonomiska potentialen hos ett P2X2P­system bestående av ett gaskombikraftverk i anslutning till en elektrolysator i det italienska kraftnätet. En dynamisk, tekno­ekonomisk modell av både vätgas­ och ammoniakbaserade P2X2P­system samt en vinstmaximerande kontrollstrategi har utvecklats. En modell över en PEMelektrolysator har även utvecklats och validerats gentemot experimentella data. Införandet av ett P2X2P­system till kraftverket påvisade en teknisk förbättringspotential genom ett minskat antal uppstarter samt en mer jämn uteffekt. Huruvida denna tekniska förbättring också medför ekonomisk and miljömässig förbättring eller ej kvarstår att påvisa. Detta då nuvärdet minskade samtidigt som koldioxidutsläppen per producerad kilowatttimme ökade vid införandet av P2X2P­systemet. Då den producerade energibäraren, i form av vätgas eller ammoniak, enbart användes för att ersätta fossilgas som bränsle i kraftverket påvisades marginell skillnad i presetanda mellan de två systemen. De större kostnaderna som medförs av ett ammoniak­baserat system pekar därför på att ett vätgas­baserat system vore att föredra under sådana förutsättningar.

A nickel alloy with high chrome and molybdenum content was found to form a highly resistive and passive oxide layer. The donor density and mobility of ions in the oxide layer has been determined as a function of the electrical potential when alkaline water layers are on the alloy surface in order to account for the relative inertness of the nickel alloy in corrosive environments.